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[thirdparty/util-linux.git] / libmount / src / tab.c

/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
 * This file is part of libmount from util-linux project.
 *
 * Copyright (C) 2008-2018 Karel Zak <kzak@redhat.com>
 *
 * libmount is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 */

/**
 * SECTION: table
 * @title: Table of filesystems
 * @short_description: container for entries from fstab, mtab or mountinfo
 *
 * Note that mnt_table_find_* functions are mount(8) compatible. These functions
 * try to find an entry in more iterations, where the first attempt is always
 * based on comparison with unmodified (non-canonicalized or un-evaluated)
 * paths or tags. For example a fstab with two entries:
 * <informalexample>
 *   <programlisting>
 *      LABEL=foo       /foo    auto   rw
 *      /dev/foo        /foo    auto   rw
 *  </programlisting>
 * </informalexample>
 *
 * where both lines are used for the *same* device, then
 * <informalexample>
 *  <programlisting>
 *      mnt_table_find_source(tb, "/dev/foo", &fs);
 *  </programlisting>
 * </informalexample>
 * will returns the second line, and
 * <informalexample>
 *  <programlisting>
 *      mnt_table_find_source(tb, "LABEL=foo", &fs);
 *  </programlisting>
 * </informalexample>
 * will returns the first entry, and
 * <informalexample>
 *  <programlisting>
 *      mnt_table_find_source(tb, "UUID=anyuuid", &fs);
 *  </programlisting>
 * </informalexample>
 * will return the first entry (if UUID matches with the device).
 */
#include <blkid.h>

#include "mountP.h"
#include "strutils.h"
#include "loopdev.h"
#include "fileutils.h"
#include "canonicalize.h"

int is_mountinfo(struct libmnt_table *tb)
{
        struct libmnt_fs *fs;

        if (!tb)
                return 0;

        fs = list_first_entry(&tb->ents, struct libmnt_fs, ents);
        if (fs && mnt_fs_is_kernel(fs) && mnt_fs_get_root(fs))
                return 1;

        return 0;
}

/**
 * mnt_new_table:
 *
 * The tab is a container for struct libmnt_fs entries that usually represents a fstab,
 * mtab or mountinfo file from your system.
 *
 * See also mnt_table_parse_file().
 *
 * Returns: newly allocated tab struct.
 */
struct libmnt_table *mnt_new_table(void)
{
        struct libmnt_table *tb = NULL;

        tb = calloc(1, sizeof(*tb));
        if (!tb)
                return NULL;

        DBG(TAB, ul_debugobj(tb, "alloc"));
        tb->refcount = 1;
        INIT_LIST_HEAD(&tb->ents);
        return tb;
}

/**
 * mnt_reset_table:
 * @tb: tab pointer
 *
 * Removes all entries (filesystems) from the table. The filesystems with zero
 * reference count will be deallocated.
 *
 * Returns: 0 on success or negative number in case of error.
 */
int mnt_reset_table(struct libmnt_table *tb)
{
        if (!tb)
                return -EINVAL;

        DBG(TAB, ul_debugobj(tb, "reset"));

        while (!list_empty(&tb->ents)) {
                struct libmnt_fs *fs = list_entry(tb->ents.next,
                                                  struct libmnt_fs, ents);
                mnt_table_remove_fs(tb, fs);
        }

        tb->nents = 0;
        mnt_table_reset_listmount(tb);

        return 0;
}

/**
 * mnt_ref_table:
 * @tb: table pointer
 *
 * Increments reference counter.
 */
void mnt_ref_table(struct libmnt_table *tb)
{
        if (tb) {
                tb->refcount++;
                /*DBG(FS, ul_debugobj(tb, "ref=%d", tb->refcount));*/
        }
}

/**
 * mnt_unref_table:
 * @tb: table pointer
 *
 * De-increments reference counter, on zero the @tb is automatically
 * deallocated by mnt_free_table().
 */
void mnt_unref_table(struct libmnt_table *tb)
{
        if (tb) {
                tb->refcount--;
                /*DBG(FS, ul_debugobj(tb, "unref=%d", tb->refcount));*/
                if (tb->refcount <= 0)
                        mnt_free_table(tb);
        }
}


/**
 * mnt_free_table:
 * @tb: tab pointer
 *
 * Deallocates the table. This function does not care about reference count. Don't
 * use this function directly -- it's better to use mnt_unref_table().
 *
 * The table entries (filesystems) are unreferenced by mnt_reset_table() and
 * cache by mnt_unref_cache().
 */
void mnt_free_table(struct libmnt_table *tb)
{
        if (!tb)
                return;

        mnt_reset_table(tb);
        DBG(TAB, ul_debugobj(tb, "free [refcount=%d]", tb->refcount));

        mnt_unref_cache(tb->cache);
        free(tb->comm_intro);
        free(tb->comm_tail);

        free(tb->lsmnt);
        tb->lsmnt = NULL;

        mnt_unref_statmnt(tb->stmnt);
        tb->stmnt = NULL;

        free(tb);
}

/**
 * mnt_table_get_nents:
 * @tb: pointer to tab
 *
 * Returns: number of entries in table.
 */
int mnt_table_get_nents(struct libmnt_table *tb)
{
        return tb ? tb->nents : 0;
}

/**
 * mnt_table_is_empty:
 * @tb: pointer to tab
 *
 * Returns: 1 if the table is without filesystems, or 0.
 */
int mnt_table_is_empty(struct libmnt_table *tb)
{
        return tb == NULL || list_empty(&tb->ents) ? 1 : 0;
}

/**
 * mnt_table_set_userdata:
 * @tb: pointer to tab
 * @data: pointer to user data
 *
 * Sets pointer to the private user data.
 *
 * Returns: 0 on success or negative number in case of error.
 */
int mnt_table_set_userdata(struct libmnt_table *tb, void *data)
{
        if (!tb)
                return -EINVAL;

        tb->userdata = data;
        return 0;
}

/**
 * mnt_table_get_userdata:
 * @tb: pointer to tab
 *
 * Returns: pointer to user's data.
 */
void *mnt_table_get_userdata(struct libmnt_table *tb)
{
        return tb ? tb->userdata : NULL;
}

/**
 * mnt_table_enable_comments:
 * @tb: pointer to tab
 * @enable: TRUE or FALSE
 *
 * Enables parsing of comments.
 *
 * The initial (intro) file comment is accessible by
 * mnt_table_get_intro_comment(). The intro and the comment of the first fstab
 * entry has to be separated by blank line.  The filesystem comments are
 * accessible by mnt_fs_get_comment(). The trailing fstab comment is accessible
 * by mnt_table_get_trailing_comment().
 *
 * <informalexample>
 *  <programlisting>
 *      #
 *      # Intro comment
 *      #
 *
 *      # this comments belongs to the first fs
 *      LABEL=foo /mnt/foo auto defaults 1 2
 *      # this comments belongs to the second fs
 *      LABEL=bar /mnt/bar auto defaults 1 2
 *      # trailing comment
 *  </programlisting>
 * </informalexample>
 */
void mnt_table_enable_comments(struct libmnt_table *tb, int enable)
{
        if (tb)
                tb->comms = enable;
}

/**
 * mnt_table_with_comments:
 * @tb: pointer to table
 *
 * Returns: 1 if comments parsing is enabled, or 0.
 */
int mnt_table_with_comments(struct libmnt_table *tb)
{
        assert(tb);
        return tb ? tb->comms : 0;
}

/**
 * mnt_table_get_intro_comment:
 * @tb: pointer to tab
 *
 * Returns: initial comment in tb
 */
const char *mnt_table_get_intro_comment(struct libmnt_table *tb)
{
        return tb ? tb->comm_intro : NULL;
}

/**
 * mnt_table_set_into_comment:
 * @tb: pointer to tab
 * @comm: comment or NULL
 *
 * Sets the initial comment in tb.
 *
 * Returns: 0 on success or negative number in case of error.
 */
int mnt_table_set_intro_comment(struct libmnt_table *tb, const char *comm)
{
        return strdup_to_struct_member(tb, comm_intro, comm);
}

/**
 * mnt_table_append_into_comment:
 * @tb: pointer to tab
 * @comm: comment of NULL
 *
 * Appends the initial comment in tb.
 *
 * Returns: 0 on success or negative number in case of error.
 */
int mnt_table_append_intro_comment(struct libmnt_table *tb, const char *comm)
{
        if (!tb)
                return -EINVAL;
        return ul_strappend(&tb->comm_intro, comm);
}

/**
 * mnt_table_get_trailing_comment:
 * @tb: pointer to tab
 *
 * Returns: table trailing comment
 */
const char *mnt_table_get_trailing_comment(struct libmnt_table *tb)
{
        return tb ? tb->comm_tail : NULL;
}

/**
 * mnt_table_set_trailing_comment
 * @tb: pointer to tab
 * @comm: comment string
 *
 * Sets the trailing comment in table.
 *
 * Returns: 0 on success or negative number in case of error.
 */
int mnt_table_set_trailing_comment(struct libmnt_table *tb, const char *comm)
{
        return strdup_to_struct_member(tb, comm_tail, comm);
}

/**
 * mnt_table_append_trailing_comment:
 * @tb: pointer to tab
 * @comm: comment of NULL
 *
 * Appends to the trailing table comment.
 *
 * Returns: 0 on success or negative number in case of error.
 */
int mnt_table_append_trailing_comment(struct libmnt_table *tb, const char *comm)
{
        if (!tb)
                return -EINVAL;
        return ul_strappend(&tb->comm_tail, comm);
}

/**
 * mnt_table_set_cache:
 * @tb: pointer to tab
 * @mpc: pointer to struct libmnt_cache instance
 *
 * Sets up a cache for canonicalized paths and evaluated tags (LABEL/UUID). The
 * cache is recommended for mnt_table_find_*() functions.
 *
 * The cache could be shared between more tabs. Be careful when you share the
 * same cache between more threads -- currently the cache does not provide any
 * locking method.
 *
 * This function increments cache reference counter. It's recommended to use
 * mnt_unref_cache() after mnt_table_set_cache() if you want to keep the cache
 * referenced by @tb only.
 *
 * See also mnt_new_cache().
 *
 * Returns: 0 on success or negative number in case of error.
 */
int mnt_table_set_cache(struct libmnt_table *tb, struct libmnt_cache *mpc)
{
        if (!tb)
                return -EINVAL;

        mnt_ref_cache(mpc);                     /* new */
        mnt_unref_cache(tb->cache);             /* old */
        tb->cache = mpc;
        return 0;
}

/**
 * mnt_table_get_cache:
 * @tb: pointer to tab
 *
 * Returns: pointer to struct libmnt_cache instance or NULL.
 */
struct libmnt_cache *mnt_table_get_cache(struct libmnt_table *tb)
{
        return tb ? tb->cache : NULL;
}

/**
 * mnt_table_refer_statmnt:
 * @tb: pointer to tab
 * @sm: statmount setting or NULL
 *
 * Add a reference to the statmount() setting in the table (see
 * mnt_new_statmnt() function, etc.).  This reference will automatically be
 * used for any newly added filesystems in the @tb, eliminating the need for
 * extra mnt_fs_refer_statmnt() calls for each filesystem.
 *
 * The reference is not removed by mnt_reset_table(), use NULL as @sm to
 * remove the reference.
 *
 * Returns: 0 on success or negative number in case of error.
 *
 * Since: 2.41
 */
int mnt_table_refer_statmnt(struct libmnt_table *tb, struct libmnt_statmnt *sm)
{
        if (!tb)
                return -EINVAL;
        if (tb->stmnt == sm)
                return 0;

        mnt_unref_statmnt(tb->stmnt);
        mnt_ref_statmnt(sm);

        DBG(TAB, ul_debugobj(tb, "refer statmnt"));

        tb->stmnt = sm;
        return 0;
}

/**
 * mnt_table_find_fs:
 * @tb: tab pointer
 * @fs: entry to look for
 *
 * Checks if @fs is part of table @tb.
 *
 * Returns: index of @fs in table, 0 if not found or negative number in case of error.
 *
 * Since: 2.34
 */
int mnt_table_find_fs(struct libmnt_table *tb, struct libmnt_fs *fs)
{
        struct list_head *p;
        int i = 0;

        if (!tb || !fs)
                return -EINVAL;

        if (list_empty(&fs->ents))
                return 0;

        /* Let's use directly list rather than mnt_table_next_fs() as we
         * compare list entry with fs only.
         */
        list_for_each(p, &tb->ents) {
                ++i;
                if (list_entry(p, struct libmnt_fs, ents) == fs)
                        return i;
        }

        return 0;
}

/**
 * mnt_table_add_fs:
 * @tb: tab pointer
 * @fs: new entry
 *
 * Adds a new entry to tab and increment @fs reference counter. Don't forget to
 * use mnt_unref_fs() after mnt_table_add_fs() you want to keep the @fs
 * referenced by the table only.
 *
 * Returns: 0 on success or negative number in case of error.
 */
int mnt_table_add_fs(struct libmnt_table *tb, struct libmnt_fs *fs)
{
        if (!tb || !fs)
                return -EINVAL;

        if (fs->tab)
                return -EBUSY;

        mnt_ref_fs(fs);
        list_add_tail(&fs->ents, &tb->ents);
        fs->tab = tb;
        tb->nents++;

        DBG(TAB, ul_debugobj(tb, "add entry: %s %s",
                        mnt_fs_get_source(fs), mnt_fs_get_target(fs)));
        if (tb->stmnt)
                mnt_fs_refer_statmnt(fs, tb->stmnt);

        return 0;
}

static int __table_insert_fs(
                        struct libmnt_table *tb, int before,
                        struct libmnt_fs *pos, struct libmnt_fs *fs)
{
        if (!pos)
                list_add_tail(&fs->ents, &tb->ents);
        else if (before)
                list_add_tail(&fs->ents, &pos->ents);
        else
                list_add(&fs->ents, &pos->ents);

        fs->tab = tb;
        tb->nents++;

        if (mnt_fs_get_uniq_id(fs)) {
                DBG(TAB, ul_debugobj(tb, "insert entry: %" PRIu64, mnt_fs_get_uniq_id(fs)));
        } else {
                DBG(TAB, ul_debugobj(tb, "insert entry: %s %s",
                        mnt_fs_get_source(fs), mnt_fs_get_target(fs)));
        }

        if (tb->stmnt)
                mnt_fs_refer_statmnt(fs, tb->stmnt);

        return 0;
}

/**
 * mnt_table_insert_fs:
 * @tb: tab pointer
 * @before: 1 to insert before pos, 0 to insert after pos
 * @pos: entry to specify position or NULL
 * @fs: new entry
 *
 * Adds a new entry to @tb before or after a specific table entry @pos. If the
 * @pos is NULL than add the begin of the @tab if @before is 1; or to the tail
 * of the @tb if @before is 0.
 *
 * This function increments reference to @fs. Don't forget to use
 * mnt_unref_fs() after mnt_table_insert_fs() if you want to keep the @fs
 * referenced by the table only.
 *
 * Returns: 0 on success or negative number in case of error.
 *
 * Since: 2.34
 */
int mnt_table_insert_fs(struct libmnt_table *tb, int before,
                        struct libmnt_fs *pos, struct libmnt_fs *fs)
{
        if (!tb || !fs)
                return -EINVAL;

        if (fs->tab)
                return -EBUSY;

        if (pos && pos->tab != tb)
                return -ENOENT;

        mnt_ref_fs(fs);
        return __table_insert_fs(tb, before, pos, fs);
}

/**
 * mnt_table_move_fs:
 * @src: tab pointer of source table
 * @dst: tab pointer of destination table
 * @before: 1 to move before position, 0 to move after position
 * @pos: entry to specify position or NULL
 * @fs: entry to move
 *
 * Removes @fs from @src table and adds it before/after a specific entry @pos
 * of @dst table. If the @pos is NULL than add the begin of the @dst if @before
 * is 1; or to the tail of the @dst if @before is 0.
 *
 * The reference counter of @fs is not modified.
 *
 * Returns: 0 on success or negative number in case of error.
 *
 * Since: 2.34
 */
int mnt_table_move_fs(struct libmnt_table *src, struct libmnt_table *dst,
                      int before, struct libmnt_fs *pos, struct libmnt_fs *fs)
{
        if (!src || !dst || !fs)
                return -EINVAL;

        if (fs->tab != src || (pos && pos->tab != dst))
                return -ENOENT;

        /* remove from source */
        list_del_init(&fs->ents);
        src->nents--;

        /* insert to the destination */
        return __table_insert_fs(dst, before, pos, fs);
}


/**
 * mnt_table_remove_fs:
 * @tb: tab pointer
 * @fs: new entry
 *
 * Removes the @fs from the table and de-increment reference counter of the @fs. The
 * filesystem with zero reference counter will be deallocated. Don't forget to use
 * mnt_ref_fs() before call mnt_table_remove_fs() if you want to use @fs later.
 *
 * Returns: 0 on success or negative number in case of error.
 */
int mnt_table_remove_fs(struct libmnt_table *tb, struct libmnt_fs *fs)
{
        if (!tb || !fs || fs->tab != tb)
                return -EINVAL;

        fs->tab = NULL;
        list_del_init(&fs->ents);

        mnt_unref_fs(fs);
        tb->nents--;
        return 0;
}

static inline struct libmnt_fs *get_parent_fs(struct libmnt_table *tb, struct libmnt_fs *fs)
{
        struct libmnt_iter itr;
        struct libmnt_fs *x;
        int parent_id = mnt_fs_get_parent_id(fs);

        mnt_reset_iter(&itr, MNT_ITER_FORWARD);
        while (mnt_table_next_fs(tb, &itr, &x) == 0) {
                if (mnt_fs_get_id(x) == parent_id)
                        return x;
        }

        return NULL;
}

/**
 * mnt_table_get_root_fs:
 * @tb: mountinfo file (/proc/self/mountinfo)
 * @root: NULL or returns pointer to the root filesystem (/)
 *
 * The function uses the parent ID from the mountinfo file to determine the
 * root filesystem (the filesystem with the smallest ID with parent ID missing
 * in the table). The function is designed mostly for applications where it is
 * necessary to sort mountpoints by IDs to get the tree of the mountpoints
 * (e.g. findmnt default output).
 *
 * If you're not sure, then use
 *
 *      mnt_table_find_target(tb, "/", MNT_ITER_BACKWARD);
 *
 * this is more robust and usable for arbitrary tab files (including fstab).
 *
 * Returns: 0 on success or negative number in case of error.
 */
int mnt_table_get_root_fs(struct libmnt_table *tb, struct libmnt_fs **root)
{
        struct libmnt_iter itr;
        struct libmnt_fs *fs, *root_fs = NULL;
        int root_id = 0;

        if (!tb || !is_mountinfo(tb))
                return -EINVAL;

        DBG(TAB, ul_debugobj(tb, "lookup root fs"));

        /* get smallest possible ID from the table */
        mnt_reset_iter(&itr, MNT_ITER_FORWARD);
        while (mnt_table_next_fs(tb, &itr, &fs) == 0) {
                int id = mnt_fs_get_parent_id(fs);

                if (!root_fs || id < root_id) {
                        root_fs = fs;
                        root_id = id;
                }
        }

        /* go to the root node by "parent_id -> id" relation */
        while (root_fs) {
                struct libmnt_fs *x = get_parent_fs(tb, root_fs);
                if (!x || x == root_fs)
                        break;
                DBG(TAB, ul_debugobj(tb, " messy mountinfo, walk to %s", mnt_fs_get_target(x)));
                root_fs = x;
        }

        if (root)
                *root = root_fs;

        return root_fs ? 0 : -EINVAL;
}

/**
 * mnt_table_next_child_fs:
 * @tb: mountinfo file (/proc/self/mountinfo)
 * @itr: iterator
 * @parent: parental FS
 * @chld: NULL or returns the next child filesystem
 *
 * Since version 2.40, the filesystems are returned in the order specified by
 * @itr. In the old versions the derection is always MNT_ITER_FORWARD.
 *
 * Returns: 0 on success, negative number in case of error or 1 at the end of list.
 */
int mnt_table_next_child_fs(struct libmnt_table *tb, struct libmnt_iter *itr,
                        struct libmnt_fs *parent, struct libmnt_fs **chld)
{
        struct libmnt_fs *fs, *chfs = NULL;
        int parent_id, lastchld_id = 0, chld_id = 0;
        int direction;

        if (!tb || !itr || !parent || !is_mountinfo(tb))
                return -EINVAL;

        DBG(TAB, ul_debugobj(tb, "lookup next child of '%s'",
                                mnt_fs_get_target(parent)));
        parent_id = mnt_fs_get_id(parent);
        direction = mnt_iter_get_direction(itr);

        /* get ID of the previously returned child */
        if (itr->head && itr->p != itr->head) {
                fs = MNT_ITER_GET_ENTRY(itr, struct libmnt_fs, ents);
                MNT_ITER_ITERATE(itr);
                lastchld_id = mnt_fs_get_id(fs);
        }

        mnt_reset_iter(itr, direction);
        while (mnt_table_next_fs(tb, itr, &fs) == 0) {
                int id;

                if (mnt_fs_get_parent_id(fs) != parent_id)
                        continue;

                id = mnt_fs_get_id(fs);

                /* avoid an infinite loop. This only happens in rare cases
                 * such as in early userspace when the rootfs is its own parent */
                if (id == parent_id)
                        continue;

                if (direction == MNT_ITER_FORWARD) {
                        /* return in the order of mounting */
                        if ((!lastchld_id || id > lastchld_id) &&
                            (!chfs || id < chld_id)) {
                                chfs = fs;
                                chld_id = id;
                        }
                } else {
                        /* return last child first */
                        if ((!lastchld_id || id < lastchld_id) &&
                            (!chfs || id > chld_id)) {
                                chfs = fs;
                                chld_id = id;
                        }
                }
        }

        if (chld)
                *chld = chfs;
        if (!chfs)
                return 1;       /* end of iterator */

        /* set the iterator to the @chfs for the next call */
        mnt_table_set_iter(tb, itr, chfs);

        return 0;
}

/**
 * mnt_table_over_fs:
 * @tb: tab pointer
 * @parent: pointer to parental FS
 * @child: returns pointer to FS which over-mounting parent (optional)
 *
 * This function returns by @child the first filesystenm which is over-mounted
 * on @parent. It means the mountpoint of @child is the same as for @parent and
 * parent->id is the same as child->parent_id.
 *
 * Note that you need to call this function in loop until it returns 1 to get
 * the highest filesystem.
 *
 * Example:
 * <informalexample>
 *   <programlisting>
 *      while (mnt_table_over_fs(tb, cur, &over) == 0) {
 *              printf("%s overmounted by %d\n", mnt_fs_get_target(cur), mnt_fs_get_id(over));
 *              cur = over;
 *      }
 *   </programlisting>
 * </informalexample>
 *
 * Returns: 0 on success, negative number in case of error or 1 at the end of list.
 */
int mnt_table_over_fs(struct libmnt_table *tb, struct libmnt_fs *parent,
                      struct libmnt_fs **child)
{
        struct libmnt_iter itr;
        struct libmnt_fs *fs = NULL;
        int id;
        const char *tgt;

        if (!tb || !parent || !is_mountinfo(tb))
                return -EINVAL;

        if (child)
                *child = NULL;

        mnt_reset_iter(&itr, MNT_ITER_FORWARD);
        id = mnt_fs_get_id(parent);
        tgt = mnt_fs_get_target(parent);

        while (mnt_table_next_fs(tb, &itr, &fs) == 0) {
                if (mnt_fs_get_parent_id(fs) == id &&
                    mnt_fs_streq_target(fs, tgt) == 1) {
                        if (child)
                                *child = fs;
                        return 0;
                }
        }

        return 1;       /* nothing */
}

/**
 * mnt_table_next_fs:
 * @tb: tab pointer
 * @itr: iterator
 * @fs: NULL or returns the next tab entry
 *
 * Returns: 0 on success, negative number in case of error or 1 at the end of list.
 *
 * Example:
 * <informalexample>
 *   <programlisting>
 *      while(mnt_table_next_fs(tb, itr, &fs) == 0) {
 *              const char *dir = mnt_fs_get_target(fs);
 *              printf("mount point: %s\n", dir);
 *      }
 *   </programlisting>
 * </informalexample>
 *
 * lists all mountpoints from fstab in reverse order.
 */
int mnt_table_next_fs(struct libmnt_table *tb, struct libmnt_iter *itr, struct libmnt_fs **fs)
{
        int rc = 1;

        if (!tb || !itr)
                return -EINVAL;
        if (fs)
                *fs = NULL;
#ifdef HAVE_STATMOUNT_API
        if (mnt_table_want_listmount(tb) &&
            (list_empty(&tb->ents) || itr->p == itr->head)) {
                struct list_head *prev = NULL;

                if (itr->p)
                        prev = IS_ITER_FORWARD(itr) ? itr->p->prev : itr->p->next;
                rc =  mnt_table_next_lsmnt(tb, itr->direction);
                if (rc)
                        return rc;
                MNT_ITER_INIT(itr, &tb->ents);
                if (prev) {
                        itr->p = prev;
                        MNT_ITER_ITERATE(itr);
                }
        }
#endif
        if (!itr->head)
                MNT_ITER_INIT(itr, &tb->ents);
        if (itr->p != itr->head) {
                if (fs)
                        *fs = MNT_ITER_GET_ENTRY(itr, struct libmnt_fs, ents);
                MNT_ITER_ITERATE(itr);
                rc = 0;
        }

        return rc;
}

/**
 * mnt_table_first_fs:
 * @tb: tab pointer
 * @fs: NULL or returns the first tab entry
 *
 * Returns: 0 on success, negative number in case of error or 1 at the end of list.
 */
int mnt_table_first_fs(struct libmnt_table *tb, struct libmnt_fs **fs)
{
        if (!tb)
                return -EINVAL;
        if (list_empty(&tb->ents))
                return 1;
        if (fs)
                *fs = list_first_entry(&tb->ents, struct libmnt_fs, ents);
        return 0;
}

/**
 * mnt_table_last_fs:
 * @tb: tab pointer
 * @fs: NULL or returns the last tab entry
 *
 * Returns: 0 on success, negative number in case of error or 1 at the end of list.
 */
int mnt_table_last_fs(struct libmnt_table *tb, struct libmnt_fs **fs)
{
        if (!tb)
                return -EINVAL;
        if (list_empty(&tb->ents))
                return 1;
        if (fs)
                *fs = list_last_entry(&tb->ents, struct libmnt_fs, ents);
        return 0;
}

/**
 * mnt_table_find_next_fs:
 * @tb: table
 * @itr: iterator
 * @match_func: function returning 1 or 0
 * @userdata: extra data for match_func
 * @fs: NULL or returns pointer to the next matching table entry
 *
 * This function allows searching in @tb.
 *
 * Returns: negative number in case of error, 1 at end of table or 0 o success.
 */
int mnt_table_find_next_fs(struct libmnt_table *tb, struct libmnt_iter *itr,
                int (*match_func)(struct libmnt_fs *, void *), void *userdata,
                struct libmnt_fs **fs)
{
        struct libmnt_fs *re = NULL;
        int match = 0;

        if (!tb || !itr || !match_func)
                return -EINVAL;

        DBG(TAB, ul_debugobj(tb, "lookup next fs"));

        if (fs)
                *fs = NULL;
        if (!itr->head)
                MNT_ITER_INIT(itr, &tb->ents);

        while (!match) {
                if (itr->p != itr->head) {
                        re = MNT_ITER_GET_ENTRY(itr, struct libmnt_fs, ents);
                        MNT_ITER_ITERATE(itr);
                } else
                        return 1;       /*end */

                match = match_func(re, userdata);
        }

        if (fs)
                *fs = re;
        return 0;
}

static int mnt_table_move_parent(struct libmnt_table *tb, int oldid, int newid)
{
        struct libmnt_iter itr;
        struct libmnt_fs *fs;

        if (!tb)
                return -EINVAL;
        if (list_empty(&tb->ents))
                return 0;

        DBG(TAB, ul_debugobj(tb, "moving parent ID from %d -> %d", oldid, newid));
        mnt_reset_iter(&itr, MNT_ITER_FORWARD);

        while (mnt_table_next_fs(tb, &itr, &fs) == 0) {
                if (fs->parent == oldid)
                        fs->parent = newid;
        }
        return 0;
}

/**
 * mnt_table_uniq_fs:
 * @tb: table
 * @flags: MNT_UNIQ_*
 * @cmp: function to compare filesystems
 *
 * This function de-duplicate the @tb, but does not change order of the
 * filesystems. The @cmp function has to return 0 if the filesystems are
 * equal, otherwise non-zero.
 *
 * The default is to keep in the table later mounted filesystems (function uses
 * backward mode iterator).
 *
 * @MNT_UNIQ_FORWARD:  remove later mounted filesystems
 * @MNT_UNIQ_KEEPTREE: keep parent->id relationship still valid
 *
 * Returns: negative number in case of error, or 0 o success.
 */
int mnt_table_uniq_fs(struct libmnt_table *tb, int flags,
                                int (*cmp)(struct libmnt_table *,
                                           struct libmnt_fs *,
                                           struct libmnt_fs *))
{
        struct libmnt_iter itr;
        struct libmnt_fs *fs;
        int direction = MNT_ITER_BACKWARD;

        if (!tb || !cmp)
                return -EINVAL;
        if (list_empty(&tb->ents))
                return 0;

        if (flags & MNT_UNIQ_FORWARD)
                direction = MNT_ITER_FORWARD;

        DBG(TAB, ul_debugobj(tb, "de-duplicate"));
        mnt_reset_iter(&itr, direction);

        if ((flags & MNT_UNIQ_KEEPTREE) && !is_mountinfo(tb))
                flags &= ~MNT_UNIQ_KEEPTREE;

        while (mnt_table_next_fs(tb, &itr, &fs) == 0) {
                int want = 1;
                struct libmnt_iter xtr;
                struct libmnt_fs *x;

                mnt_reset_iter(&xtr, direction);
                while (want && mnt_table_next_fs(tb, &xtr, &x) == 0) {
                        if (fs == x)
                                break;
                        want = cmp(tb, x, fs) != 0;
                }

                if (!want) {
                        if (flags & MNT_UNIQ_KEEPTREE)
                                mnt_table_move_parent(tb, mnt_fs_get_id(fs),
                                                          mnt_fs_get_parent_id(fs));

                        DBG(TAB, ul_debugobj(tb, "remove duplicate %s",
                                                mnt_fs_get_target(fs)));
                        mnt_table_remove_fs(tb, fs);
                }
        }

        return 0;
}

/**
 * mnt_table_set_iter:
 * @tb: tab pointer
 * @itr: iterator
 * @fs: tab entry
 *
 * Sets @iter to the position of @fs in the file @tb.
 *
 * Returns: 0 on success, negative number in case of error.
 */
int mnt_table_set_iter(struct libmnt_table *tb, struct libmnt_iter *itr, struct libmnt_fs *fs)
{
        if (!tb || !itr || !fs)
                return -EINVAL;

        if (fs->tab != tb)
                return -ENOENT;

        MNT_ITER_INIT(itr, &tb->ents);
        itr->p = &fs->ents;

        return 0;
}

/**
 * mnt_table_find_mountpoint:
 * @tb: tab pointer
 * @path: directory
 * @direction: MNT_ITER_{FORWARD,BACKWARD}
 *
 * Same as mnt_get_mountpoint(), except this function does not rely on
 * st_dev numbers.
 *
 * Returns: a tab entry or NULL.
 */
struct libmnt_fs *mnt_table_find_mountpoint(struct libmnt_table *tb,
                                            const char *path,
                                            int direction)
{
        char *mnt;

        if (!tb || !path || !*path)
                return NULL;
        if (direction != MNT_ITER_FORWARD && direction != MNT_ITER_BACKWARD)
                return NULL;

        DBG(TAB, ul_debugobj(tb, "lookup MOUNTPOINT: '%s'", path));

        if (!mnt_is_path(path))
                return NULL;

        mnt = strdup(path);
        if (!mnt)
                return NULL;

        do {
                char *p;
                struct libmnt_fs *fs;

                fs = mnt_table_find_target(tb, mnt, direction);
                if (fs) {
                        free(mnt);
                        return fs;
                }

                p = stripoff_last_component(mnt);
                if (!p)
                        break;
        } while (mnt && *(mnt + 1) != '\0');

        free(mnt);
        return mnt_table_find_target(tb, "/", direction);
}

/**
 * mnt_table_find_target:
 * @tb: tab pointer
 * @path: mountpoint directory
 * @direction: MNT_ITER_{FORWARD,BACKWARD}
 *
 * Try to lookup an entry in the given tab, three iterations are possible, the first
 * with @path, the second with realpath(@path) and the third with realpath(@path)
 * against realpath(fs->target). The 2nd and 3rd iterations are not performed when
 * the @tb cache is not set (see mnt_table_set_cache()). If
 * mnt_cache_set_targets(cache, mtab) was called, the 3rd iteration skips any
 * @fs->target found in @mtab (see mnt_resolve_target()).
 *
 * Returns: a tab entry or NULL.
 */
struct libmnt_fs *mnt_table_find_target(struct libmnt_table *tb, const char *path, int direction)
{
        struct libmnt_iter itr;
        struct libmnt_fs *fs = NULL;
        char *cn;

        if (!tb || !path || !*path)
                return NULL;
        if (direction != MNT_ITER_FORWARD && direction != MNT_ITER_BACKWARD)
                return NULL;

        DBG(TAB, ul_debugobj(tb, "lookup TARGET: '%s'", path));

        /* native @target */
        mnt_reset_iter(&itr, direction);
        while(mnt_table_next_fs(tb, &itr, &fs) == 0) {
                if (mnt_fs_streq_target(fs, path))
                        return fs;
        }

        /* try absolute path */
        if (is_relative_path(path) && (cn = absolute_path(path))) {
                DBG(TAB, ul_debugobj(tb, "lookup absolute TARGET: '%s'", cn));
                mnt_reset_iter(&itr, direction);
                while (mnt_table_next_fs(tb, &itr, &fs) == 0) {
                        if (mnt_fs_streq_target(fs, cn)) {
                                free(cn);
                                return fs;
                        }
                }
                free(cn);
        }

        if (!tb->cache || !(cn = mnt_resolve_path(path, tb->cache)))
                return NULL;

        DBG(TAB, ul_debugobj(tb, "lookup canonical TARGET: '%s'", cn));

        /* canonicalized paths in struct libmnt_table */
        mnt_reset_iter(&itr, direction);
        while(mnt_table_next_fs(tb, &itr, &fs) == 0) {
                if (mnt_fs_streq_target(fs, cn))
                        return fs;
        }

        /* non-canonical path in struct libmnt_table
         * -- note that mountpoint in /proc/self/mountinfo is already
         *    canonicalized by the kernel
         */
        mnt_reset_iter(&itr, direction);
        while(mnt_table_next_fs(tb, &itr, &fs) == 0) {
                char *p;

                if (!fs->target
                    || mnt_fs_is_swaparea(fs)
                    || mnt_fs_is_kernel(fs)
                    || (*fs->target == '/' && *(fs->target + 1) == '\0'))
                       continue;

                p = mnt_resolve_target(fs->target, tb->cache);
                /* both canonicalized, strcmp() is fine here */
                if (p && strcmp(cn, p) == 0)
                        return fs;
        }
        return NULL;
}

/**
 * mnt_table_find_srcpath:
 * @tb: tab pointer
 * @path: source path (devname or dirname) or NULL
 * @direction: MNT_ITER_{FORWARD,BACKWARD}
 *
 * Try to lookup an entry in the given tab, four iterations are possible, the first
 * with @path, the second with realpath(@path), the third with tags (LABEL, UUID, ..)
 * from @path and the fourth with realpath(@path) against realpath(entry->srcpath).
 *
 * The 2nd, 3rd and 4th iterations are not performed when the @tb cache is not
 * set (see mnt_table_set_cache()).
 *
 * For btrfs returns tab entry for default id.
 *
 * Note that NULL is a valid source path; it will be replaced with "none". The
 * "none" is used in /proc/{mounts,self/mountinfo} for pseudo filesystems.
 *
 * Returns: a tab entry or NULL.
 */
struct libmnt_fs *mnt_table_find_srcpath(struct libmnt_table *tb, const char *path, int direction)
{
        struct libmnt_iter itr;
        struct libmnt_fs *fs = NULL;
        int ntags = 0, nents;
        char *cn;
        const char *p;

        if (!tb || !path || !*path)
                return NULL;
        if (direction != MNT_ITER_FORWARD && direction != MNT_ITER_BACKWARD)
                return NULL;

        DBG(TAB, ul_debugobj(tb, "lookup SRCPATH: '%s'", path));

        /* native paths */
        mnt_reset_iter(&itr, direction);

        while(mnt_table_next_fs(tb, &itr, &fs) == 0) {

                if (mnt_fs_streq_srcpath(fs, path)) {
#ifdef HAVE_BTRFS_SUPPORT
                        if (fs->fstype && !strcmp(fs->fstype, "btrfs")) {
                                uint64_t default_id = btrfs_get_default_subvol_id(mnt_fs_get_target(fs));
                                char *val;
                                size_t len;

                                if (default_id == UINT64_MAX)
                                        DBG(TAB, ul_debug("not found btrfs volume setting"));

                                else if (mnt_fs_get_option(fs, "subvolid", &val, &len) == 0) {
                                        uint64_t subvol_id;

                                        if (mnt_parse_offset(val, len, &subvol_id)) {
                                                DBG(TAB, ul_debugobj(tb, "failed to parse subvolid="));
                                                continue;
                                        }
                                        if (subvol_id != default_id)
                                                continue;
                                }
                        }
#endif /* HAVE_BTRFS_SUPPORT */
                        return fs;
                }
                if (mnt_fs_get_tag(fs, NULL, NULL) == 0)
                        ntags++;
        }

        if (!path || !tb->cache || !(cn = mnt_resolve_path(path, tb->cache)))
                return NULL;

        DBG(TAB, ul_debugobj(tb, "lookup canonical SRCPATH: '%s'", cn));

        nents = mnt_table_get_nents(tb);

        /* canonicalized paths in struct libmnt_table */
        if (ntags < nents) {
                mnt_reset_iter(&itr, direction);
                while(mnt_table_next_fs(tb, &itr, &fs) == 0) {
                        if (mnt_fs_streq_srcpath(fs, cn))
                                return fs;
                }
        }

        /* evaluated tag */
        if (ntags) {
                int rc = mnt_cache_read_tags(tb->cache, cn);

                mnt_reset_iter(&itr, direction);

                if (rc == 0) {
                        /* @path's TAGs are in the cache */
                        while(mnt_table_next_fs(tb, &itr, &fs) == 0) {
                                const char *t, *v;

                                if (mnt_fs_get_tag(fs, &t, &v))
                                        continue;

                                if (mnt_cache_device_has_tag(tb->cache, cn, t, v))
                                        return fs;
                        }
                } else if (rc < 0 && errno == EACCES) {
                        /* @path is inaccessible, try evaluating all TAGs in @tb
                         * by udev symlinks -- this could be expensive on systems
                         * with a huge fstab/mtab */
                         while(mnt_table_next_fs(tb, &itr, &fs) == 0) {
                                 const char *t, *v, *x;
                                 if (mnt_fs_get_tag(fs, &t, &v))
                                         continue;
                                 x = mnt_resolve_tag(t, v, tb->cache);

                                 /* both canonicalized, strcmp() is fine here */
                                 if (x && strcmp(x, cn) == 0)
                                         return fs;
                         }
                }
        }

        /* non-canonicalized paths in struct libmnt_table */
        if (ntags <= nents) {
                mnt_reset_iter(&itr, direction);
                while(mnt_table_next_fs(tb, &itr, &fs) == 0) {
                        if (mnt_fs_is_netfs(fs) || mnt_fs_is_pseudofs(fs))
                                continue;
                        p = mnt_fs_get_srcpath(fs);
                        if (p)
                                p = mnt_resolve_path(p, tb->cache);

                        /* both canonicalized, strcmp() is fine here */
                        if (p && strcmp(p, cn) == 0)
                                return fs;
                }
        }

        return NULL;
}


/**
 * mnt_table_find_tag:
 * @tb: tab pointer
 * @tag: tag name (e.g "LABEL", "UUID", ...)
 * @val: tag value
 * @direction: MNT_ITER_{FORWARD,BACKWARD}
 *
 * Try to lookup an entry in the given tab, the first attempt is to lookup by @tag and
 * @val, for the second attempt the tag is evaluated (converted to the device
 * name) and mnt_table_find_srcpath() is performed. The second attempt is not
 * performed when @tb cache is not set (see mnt_table_set_cache()).

 * Returns: a tab entry or NULL.
 */
struct libmnt_fs *mnt_table_find_tag(struct libmnt_table *tb, const char *tag,
                        const char *val, int direction)
{
        struct libmnt_iter itr;
        struct libmnt_fs *fs = NULL;

        if (!tb || !tag || !*tag || !val)
                return NULL;
        if (direction != MNT_ITER_FORWARD && direction != MNT_ITER_BACKWARD)
                return NULL;

        DBG(TAB, ul_debugobj(tb, "lookup by TAG: %s %s", tag, val));

        /* look up by TAG */
        mnt_reset_iter(&itr, direction);
        while(mnt_table_next_fs(tb, &itr, &fs) == 0) {
                if (fs->tagname && fs->tagval &&
                    strcmp(fs->tagname, tag) == 0 &&
                    strcmp(fs->tagval, val) == 0)
                        return fs;
        }

        if (tb->cache) {
                /* look up by device name */
                char *cn = mnt_resolve_tag(tag, val, tb->cache);
                if (cn)
                        return mnt_table_find_srcpath(tb, cn, direction);
        }
        return NULL;
}

/**
 * mnt_table_find_target_with_option:
 * @tb: tab pointer
 * @path: mountpoint directory
 * @option: option name (e.g "subvol", "subvolid", ...)
 * @val: option value or NULL
 * @direction: MNT_ITER_{FORWARD,BACKWARD}
 *
 * Try to lookup an entry in the given tab that matches combination of @path
 * and @option. In difference to mnt_table_find_target(), only @path iteration
 * is done. No lookup by device name, no canonicalization.
 *
 * Returns: a tab entry or NULL.
 *
 * Since: 2.28
 */
struct libmnt_fs *mnt_table_find_target_with_option(
                        struct libmnt_table *tb, const char *path,
                        const char *option, const char *val, int direction)
{
        struct libmnt_iter itr;
        struct libmnt_fs *fs = NULL;
        char *optval = NULL;
        size_t optvalsz = 0, valsz = val ? strlen(val) : 0;

        if (!tb || !path || !*path || !option || !*option || !val)
                return NULL;
        if (direction != MNT_ITER_FORWARD && direction != MNT_ITER_BACKWARD)
                return NULL;

        DBG(TAB, ul_debugobj(tb, "lookup TARGET: '%s' with OPTION %s %s", path, option, val));

        /* look up by native @target with OPTION */
        mnt_reset_iter(&itr, direction);
        while (mnt_table_next_fs(tb, &itr, &fs) == 0) {
                if (mnt_fs_streq_target(fs, path)
                    && mnt_fs_get_option(fs, option, &optval, &optvalsz) == 0
                    && (!val || (optvalsz == valsz
                                 && strncmp(optval, val, optvalsz) == 0)))
                        return fs;
        }
        return NULL;
}

/**
 * mnt_table_find_source:
 * @tb: tab pointer
 * @source: TAG or path
 * @direction: MNT_ITER_{FORWARD,BACKWARD}
 *
 * This is a high-level API for mnt_table_find_{srcpath,tag}. You needn't care
 * about the @source format (device, LABEL, UUID, ...). This function parses
 * the @source and calls mnt_table_find_tag() or mnt_table_find_srcpath().
 *
 * Returns: a tab entry or NULL.
 */
struct libmnt_fs *mnt_table_find_source(struct libmnt_table *tb,
                                        const char *source, int direction)
{
        struct libmnt_fs *fs;
        char *t = NULL, *v = NULL;

        if (!tb)
                return NULL;
        if (direction != MNT_ITER_FORWARD && direction != MNT_ITER_BACKWARD)
                return NULL;

        DBG(TAB, ul_debugobj(tb, "lookup SOURCE: '%s'", source));

        if (blkid_parse_tag_string(source, &t, &v) || !mnt_valid_tagname(t))
                fs = mnt_table_find_srcpath(tb, source, direction);
        else
                fs = mnt_table_find_tag(tb, t, v, direction);

        free(t);
        free(v);

        return fs;
}

/**
 * mnt_table_find_pair
 * @tb: tab pointer
 * @source: TAG or path
 * @target: mountpoint
 * @direction: MNT_ITER_{FORWARD,BACKWARD}
 *
 * This function is implemented by mnt_fs_match_source() and
 * mnt_fs_match_target() functions. It means that this is more expensive than
 * others mnt_table_find_* function, because every @tab entry is fully evaluated.
 *
 * Returns: a tab entry or NULL.
 */
struct libmnt_fs *mnt_table_find_pair(struct libmnt_table *tb, const char *source,
                                      const char *target, int direction)
{
        struct libmnt_fs *fs = NULL;
        struct libmnt_iter itr;

        if (!tb || !target || !*target || !source || !*source)
                return NULL;
        if (direction != MNT_ITER_FORWARD && direction != MNT_ITER_BACKWARD)
                return NULL;

        DBG(TAB, ul_debugobj(tb, "lookup SOURCE: %s TARGET: %s", source, target));

        mnt_reset_iter(&itr, direction);
        while(mnt_table_next_fs(tb, &itr, &fs) == 0) {

                if (mnt_fs_match_target(fs, target, tb->cache) &&
                    mnt_fs_match_source(fs, source, tb->cache))
                        return fs;
        }

        return NULL;
}

/**
 * mnt_table_find_devno
 * @tb: /proc/self/mountinfo
 * @devno: device number
 * @direction: MNT_ITER_{FORWARD,BACKWARD}
 *
 * Note that zero could be a valid device number for the root pseudo filesystem (e.g.
 * tmpfs).
 *
 * Returns: a tab entry or NULL.
 */
struct libmnt_fs *mnt_table_find_devno(struct libmnt_table *tb,
                                       dev_t devno, int direction)
{
        struct libmnt_fs *fs = NULL;
        struct libmnt_iter itr;

        if (!tb)
                return NULL;
        if (direction != MNT_ITER_FORWARD && direction != MNT_ITER_BACKWARD)
                return NULL;

        DBG(TAB, ul_debugobj(tb, "lookup DEVNO: %d", (int) devno));

        mnt_reset_iter(&itr, direction);

        while(mnt_table_next_fs(tb, &itr, &fs) == 0) {
                if (mnt_fs_get_devno(fs) == devno)
                        return fs;
        }

        return NULL;
}

/**
 * mnt_table_find_id:
 * @tb: mount table
 * @id: classic mount ID
 *
 * See also mnt_id_from_path().
 *
 * Returns: a tab entry or NULL.
 *
 * Since: 2.41
 */
struct libmnt_fs *mnt_table_find_id(struct libmnt_table *tb, int id)
{
        struct libmnt_fs *fs = NULL;
        struct libmnt_iter itr;

        if (!tb)
                return NULL;

        DBG(TAB, ul_debugobj(tb, "lookup ID: %d", id));
        mnt_reset_iter(&itr, MNT_ITER_BACKWARD);

        while (mnt_table_next_fs(tb, &itr, &fs) == 0) {
                if (mnt_fs_get_id(fs) == id)
                        return fs;
        }

        return NULL;
}

/**
 * mnt_table_find_uniq_id:
 * @tb: mount table
 * @id: uniqie 64-bit mount ID
 *
 * See also mnt_id_from_path().
 *
 * Returns: a tab entry or NULL.
 *
 * Since: 2.41
 */
struct libmnt_fs *mnt_table_find_uniq_id(struct libmnt_table *tb, uint64_t id)
{
        struct libmnt_fs *fs = NULL;
        struct libmnt_iter itr;

        if (!tb)
                return NULL;

        DBG(TAB, ul_debugobj(tb, "lookup uniq-ID: %" PRIu64, id));
        mnt_reset_iter(&itr, MNT_ITER_BACKWARD);

        while (mnt_table_next_fs(tb, &itr, &fs) == 0) {
                if (mnt_fs_get_uniq_id(fs) == id)
                        return fs;
        }

        return NULL;
}


static char *remove_mountpoint_from_path(const char *path, const char *mnt)
{
        char *res;
        const char *p;
        size_t sz;

        sz = strlen(mnt);
        p = sz > 1 ? path + sz : path;

        res = *p ? strdup(p) : strdup("/");
        DBG(UTILS, ul_debug("%s fs-root is %s", path, res));
        return res;
}

#ifdef HAVE_BTRFS_SUPPORT
static int get_btrfs_fs_root(struct libmnt_table *tb, struct libmnt_fs *fs, char **root)
{
        char *vol = NULL, *p;
        size_t sz, volsz = 0;

        DBG(BTRFS, ul_debug("lookup for btrfs FS root"));
        *root = NULL;

        if (mnt_fs_get_option(fs, "subvolid", &vol, &volsz) == 0) {
                char *target;
                struct libmnt_fs *f;
                char subvolidstr[sizeof(stringify_value(UINT64_MAX))];

                DBG(BTRFS, ul_debug(" found subvolid=%s, checking", vol));

                assert (volsz + 1 < sizeof(stringify_value(UINT64_MAX)));
                memcpy(subvolidstr, vol, volsz);
                subvolidstr[volsz] = '\0';

                target = mnt_resolve_target(mnt_fs_get_target(fs), tb->cache);
                if (!target)
                        goto err;

                DBG(BTRFS, ul_debug(" trying target=%s subvolid=%s", target, subvolidstr));
                f = mnt_table_find_target_with_option(tb, target,
                                        "subvolid", subvolidstr,
                                        MNT_ITER_BACKWARD);
                if (!tb->cache)
                        free(target);
                if (!f)
                        goto not_found;

                /* Instead of set of BACKREF queries constructing subvol path
                 * corresponding to a particular subvolid, use the one in
                 * mountinfo. Kernel keeps subvol path up to date.
                 */
                if (mnt_fs_get_option(f, "subvol", &vol, &volsz) != 0)
                        goto not_found;

        } else if (mnt_fs_get_option(fs, "subvol", &vol, &volsz) != 0) {
                /* If fstab entry does not contain "subvol", we have to
                 * check, whether btrfs has default subvolume defined.
                 */
                uint64_t default_id;
                char *target;
                struct libmnt_fs *f;
                char default_id_str[sizeof(stringify_value(UINT64_MAX))];

                DBG(BTRFS, ul_debug(" subvolid/subvol not found, checking default"));

                default_id = btrfs_get_default_subvol_id(mnt_fs_get_target(fs));
                if (default_id == UINT64_MAX)
                        goto not_found;

                /* Volume has default subvolume. Check if it matches to
                 * the one in mountinfo.
                 *
                 * Only kernel >= 4.2 reports subvolid. On older
                 * kernels, there is no reasonable way to detect which
                 * subvolume was mounted.
                 */
                target = mnt_resolve_target(mnt_fs_get_target(fs), tb->cache);
                if (!target)
                        goto err;

                snprintf(default_id_str, sizeof(default_id_str), "%llu",
                                (unsigned long long int) default_id);

                DBG(BTRFS, ul_debug(" trying target=%s default subvolid=%s",
                                        target, default_id_str));

                f = mnt_table_find_target_with_option(tb, target,
                                        "subvolid", default_id_str,
                                        MNT_ITER_BACKWARD);
                if (!tb->cache)
                        free(target);
                if (!f)
                        goto not_found;

                /* Instead of set of BACKREF queries constructing
                 * subvol path, use the one in mountinfo. Kernel does
                 * the evaluation for us.
                 */
                DBG(BTRFS, ul_debug("setting FS root: btrfs default subvolid = %s",
                                        default_id_str));

                if (mnt_fs_get_option(f, "subvol", &vol, &volsz) != 0)
                        goto not_found;
        }

        DBG(BTRFS, ul_debug(" using subvol=%s", vol));
        sz = volsz;
        if (*vol != '/')
                sz++;
        *root = malloc(sz + 1);
        if (!*root)
                goto err;
        p = *root;
        if (*vol != '/')
                *p++ = '/';
        memcpy(p, vol, volsz);
        *(*root + sz) = '\0';
        return 0;

not_found:
        DBG(BTRFS, ul_debug(" not found btrfs volume setting"));
        return 1;
err:
        DBG(BTRFS, ul_debug(" error on btrfs volume setting evaluation"));
        return errno ? -errno : -1;
}
#endif /* HAVE_BTRFS_SUPPORT */

static const char *get_cifs_unc_subdir_path (const char *unc)
{
        /*
         *  1 or more slash:     %*[/]
         *  1 or more non-slash: %*[^/]
         *  number of byte read: %n
         */
        int share_end = 0;
        int r = sscanf(unc, "%*[/]%*[^/]%*[/]%*[^/]%n", &share_end);
        if (r == EOF || share_end == 0)
                return NULL;
        return unc + share_end;
}

/*
 * tb: /proc/self/mountinfo
 * fs: filesystem
 * mountflags: MS_BIND or 0
 * fsroot: fs-root that will probably be used in the mountinfo file
 *          for @fs after mount(2)
 *
 * For btrfs subvolumes this function returns NULL, but @fsroot properly set.
 *
 * If @tb is NULL then defaults to '/'.
 *
 * Returns: entry from @tb that will be used as a source for @fs if the @fs is
 *          bindmount.
 *
 * Don't export to library API!
 */
struct libmnt_fs *mnt_table_get_fs_root(struct libmnt_table *tb,
                                        struct libmnt_fs *fs,
                                        unsigned long mountflags,
                                        char **fsroot)
{
        char *root = NULL;
        const char *mnt = NULL;
        struct libmnt_fs *src_fs = NULL;

        assert(fs);
        assert(fsroot);

        DBG(TAB, ul_debug("lookup fs-root for '%s'", mnt_fs_get_source(fs)));

        if (tb && (mountflags & MS_BIND)) {
                const char *src, *src_root;
                char *xsrc = NULL;

                DBG(TAB, ul_debug("fs-root for bind"));

                src = xsrc = mnt_resolve_spec(mnt_fs_get_source(fs), tb->cache);
                if (src) {
                        struct libmnt_fs *f = mnt_table_find_mountpoint(tb,
                                                        src, MNT_ITER_BACKWARD);
                        if (f)
                                mnt = mnt_fs_get_target(f);
                }
                if (mnt)
                        root = remove_mountpoint_from_path(src, mnt);

                if (xsrc && !tb->cache) {
                        free(xsrc);
                        src = NULL;
                }
                if (!mnt)
                        goto err;

                src_fs = mnt_table_find_target(tb, mnt, MNT_ITER_BACKWARD);
                if (!src_fs)  {
                        DBG(TAB, ul_debug("not found '%s' in mountinfo -- using default", mnt));
                        goto dflt;
                }

                /* It's possible that fstab_fs source is subdirectory on btrfs
                 * subvolume or another bind mount. For example:
                 *
                 * /dev/sdc        /mnt/test       btrfs   subvol=/anydir
                 * /dev/sdc        /mnt/test       btrfs   defaults
                 * /mnt/test/foo   /mnt/test2      auto    bind
                 *
                 * in this case, the root for /mnt/test2 will be /anydir/foo on
                 * /dev/sdc. It means we have to compose the final root from
                 * root and src_root.
                 */
                src_root = mnt_fs_get_root(src_fs);

                DBG(FS, ul_debugobj(fs, "source root: %s, source FS root: %s", root, src_root));

                if (src_root && root && !ul_startswith(root, src_root)) {
                        if (strcmp(root, "/") == 0) {
                                free(root);
                                root = strdup(src_root);
                                if (!root)
                                        goto err;
                        } else {
                                char *tmp;
                                if (asprintf(&tmp, "%s%s", src_root, root) < 0)
                                        goto err;
                                free(root);
                                root = tmp;
                        }
                }
        }

#ifdef HAVE_BTRFS_SUPPORT
        /*
         * btrfs-subvolume mount -- get subvolume name and use it as a root-fs path
         */
        else if (tb && fs->fstype &&
                 (!strcmp(fs->fstype, "btrfs") || !strcmp(fs->fstype, "auto"))) {
                if (get_btrfs_fs_root(tb, fs, &root) < 0)
                        goto err;
        }
#endif /* HAVE_BTRFS_SUPPORT */

dflt:
        if (!root) {
                root = strdup("/");
                if (!root)
                        goto err;
        }
        *fsroot = root;

        DBG(TAB, ul_debug("FS root result: %s", root));

        return src_fs;
err:
        free(root);
        return NULL;
}


int __mnt_table_is_fs_mounted(struct libmnt_table *tb, struct libmnt_fs *fstab_fs,
                              const char *tgt_prefix)
{
        struct libmnt_iter itr;
        struct libmnt_fs *fs;

        char *root = NULL;
        char *src2 = NULL;
        const char *src = NULL, *tgt = NULL;
        char *xtgt = NULL, *tgt_buf = NULL;
        int rc = 0;
        dev_t devno = 0;

        DBG(FS, ul_debugobj(fstab_fs, "mnt_table_is_fs_mounted: target=%s, source=%s",
                                mnt_fs_get_target(fstab_fs),
                                mnt_fs_get_source(fstab_fs)));

        if (mnt_fs_is_swaparea(fstab_fs) || mnt_table_is_empty(tb)) {
                DBG(FS, ul_debugobj(fstab_fs, "- ignore (swap or no data)"));
                return 0;
        }

        if (is_mountinfo(tb)) {
                /* @tb is mountinfo, so we can try to use fs-roots */
                struct libmnt_fs *rootfs;
                int flags = 0;

                if (mnt_fs_get_option(fstab_fs, "bind", NULL, NULL) == 0 ||
                    mnt_fs_get_option(fstab_fs, "rbind", NULL, NULL) == 0)
                        flags = MS_BIND;

                rootfs = mnt_table_get_fs_root(tb, fstab_fs, flags, &root);
                if (rootfs) {
                        const char *fstype = mnt_fs_get_fstype(rootfs);

                        src = mnt_fs_get_srcpath(rootfs);
                        if (fstype && strncmp(fstype, "nfs", 3) == 0 && root) {
                                /* NFS stores the root at the end of the source */
                                src = src2 = ul_strconcat(src, root);
                                free(root);
                                root = NULL;
                        }
                }
        }

        if (!src)
                src = mnt_fs_get_source(fstab_fs);

        if (src && tb->cache && !mnt_fs_is_pseudofs(fstab_fs))
                src = mnt_resolve_spec(src, tb->cache);

        if (src && root) {
                struct stat st;

                devno = mnt_fs_get_devno(fstab_fs);
                if (!devno && mnt_safe_stat(src, &st) == 0 && S_ISBLK(st.st_mode))
                        devno = st.st_rdev;
        }

        tgt = mnt_fs_get_target(fstab_fs);

        if (!tgt || !src) {
                DBG(FS, ul_debugobj(fstab_fs, "- ignore (no source/target)"));
                goto done;
        }
        mnt_reset_iter(&itr, MNT_ITER_FORWARD);

        DBG(FS, ul_debugobj(fstab_fs, "mnt_table_is_fs_mounted: src=%s, tgt=%s, root=%s", src, tgt, root));

        while (mnt_table_next_fs(tb, &itr, &fs) == 0) {

                int eq = mnt_fs_streq_srcpath(fs, src);

                if (!eq && devno && mnt_fs_get_devno(fs) == devno)
                        eq = 1;

                if (!eq) {
                        /* The source does not match. Maybe the source is a loop
                         * device backing file.
                         */
                        uint64_t offset = 0;
                        char *val;
                        size_t len;
                        int flags = 0;

                        if (!mnt_fs_get_srcpath(fs) ||
                            !ul_startswith(mnt_fs_get_srcpath(fs), "/dev/loop"))
                                continue;       /* does not look like loopdev */

                        if (mnt_fs_get_option(fstab_fs, "offset", &val, &len) == 0) {
                                if (mnt_parse_offset(val, len, &offset)) {
                                        DBG(FS, ul_debugobj(fstab_fs, "failed to parse offset="));
                                        continue;
                                }
                                flags = LOOPDEV_FL_OFFSET;
                        }

                        DBG(FS, ul_debugobj(fs, "checking for loop: src=%s", mnt_fs_get_srcpath(fs)));
#if __linux__
                        if (!loopdev_is_used(mnt_fs_get_srcpath(fs), src, offset, 0, flags))
                                continue;

                        DBG(FS, ul_debugobj(fs, "used loop"));
#endif
                }

                if (root) {
                        const char *fstype = mnt_fs_get_fstype(fs);

                        if (fstype && (strcmp(fstype, "cifs") == 0 ||
                                       strcmp(fstype, "smb3") == 0)) {

                                const char *sub = get_cifs_unc_subdir_path(src);
                                const char *r = mnt_fs_get_root(fs);

                                if (!sub || !r || (!streq_paths(sub, r) &&
                                                   !streq_paths("/", r)))
                                        continue;
                        } else {
                                const char *r = mnt_fs_get_root(fs);
                                if (!r || strcmp(r, root) != 0)
                                        continue;
                        }
                }

                /*
                 * Compare target, try to minimize the number of situations when we
                 * need to canonicalize the path to avoid readlink() on
                 * mountpoints.
                 */
                if (!xtgt) {
                        if (tgt_prefix) {
                                const char *p = *tgt == '/' ? tgt + 1 : tgt;
                                if (!*p)
                                        tgt = tgt_prefix;       /* target is '/' */
                                else {
                                        if (asprintf(&tgt_buf, "%s/%s", tgt_prefix, p) <= 0) {
                                                rc = -ENOMEM;
                                                goto done;
                                        }
                                        tgt = tgt_buf;
                                }
                        }

                        if (mnt_fs_streq_target(fs, tgt))
                                break;
                        if (tb->cache)
                                xtgt = mnt_resolve_path(tgt, tb->cache);
                }
                if (xtgt && mnt_fs_streq_target(fs, xtgt))
                        break;
        }

        if (fs)
                rc = 1;         /* success */
done:
        free(root);
        free(tgt_buf);

        DBG(TAB, ul_debugobj(tb, "mnt_table_is_fs_mounted: %s [rc=%d]", src, rc));
        free(src2);
        return rc;
}

/**
 * mnt_table_is_fs_mounted:
 * @tb: /proc/self/mountinfo file
 * @fstab_fs: /etc/fstab entry
 *
 * Checks if the @fstab_fs entry is already in the @tb table. The "swap" is
 * ignored. This function explicitly compares the source, target and root of the
 * filesystems.
 *
 * Note that source and target are canonicalized only if a cache for @tb is
 * defined (see mnt_table_set_cache()). The target canonicalization may
 * trigger automount on autofs mountpoints!
 *
 * Don't use it if you want to know if a device is mounted, just use
 * mnt_table_find_source() on the device.
 *
 * This function is designed mostly for "mount -a".
 *
 * Returns: 0 or 1
 */
int mnt_table_is_fs_mounted(struct libmnt_table *tb, struct libmnt_fs *fstab_fs)
{
        return __mnt_table_is_fs_mounted(tb, fstab_fs, NULL);
}


#ifdef TEST_PROGRAM
#include "pathnames.h"
#include "cctype.h"

static int parser_errcb(struct libmnt_table *tb __attribute__((unused)),
                        const char *filename, int line)
{
        fprintf(stderr, "%s:%d: parse error\n", filename, line);

        return 1;       /* all errors are recoverable -- this is the default */
}

static struct libmnt_table *create_table(const char *file, int comments)
{
        struct libmnt_table *tb;

        if (!file)
                return NULL;
        tb = mnt_new_table();
        if (!tb)
                goto err;

        mnt_table_enable_comments(tb, comments);
        mnt_table_set_parser_errcb(tb, parser_errcb);

        if (mnt_table_parse_file(tb, file) != 0)
                goto err;
        return tb;
err:
        fprintf(stderr, "%s: parsing failed\n", file);
        mnt_unref_table(tb);
        return NULL;
}

static int test_copy_fs(struct libmnt_test *ts __attribute__((unused)),
                        int argc, char *argv[])
{
        struct libmnt_table *tb;
        struct libmnt_fs *fs;
        int rc = -1;

        if (argc != 2)
                return -1;

        tb = create_table(argv[1], FALSE);
        if (!tb)
                return -1;

        fs = mnt_table_find_target(tb, "/", MNT_ITER_FORWARD);
        if (!fs)
                goto done;

        printf("ORIGINAL:\n");
        mnt_fs_print_debug(fs, stdout);

        fs = mnt_copy_fs(NULL, fs);
        if (!fs)
                goto done;

        printf("COPY:\n");
        mnt_fs_print_debug(fs, stdout);
        mnt_unref_fs(fs);
        rc = 0;
done:
        mnt_unref_table(tb);
        return rc;
}

static int test_parse(struct libmnt_test *ts __attribute__((unused)),
                      int argc, char *argv[])
{
        struct libmnt_table *tb = NULL;
        struct libmnt_iter *itr = NULL;
        struct libmnt_fs *fs;
        int rc = -1;
        int parse_comments = FALSE;

        if (argc == 3 && !strcmp(argv[2], "--comments"))
                parse_comments = TRUE;

        tb = create_table(argv[1], parse_comments);
        if (!tb)
                return -1;

        itr = mnt_new_iter(MNT_ITER_FORWARD);
        if (!itr)
                goto done;

        if (mnt_table_get_intro_comment(tb))
                fprintf(stdout, "Initial comment:\n\"%s\"\n",
                                mnt_table_get_intro_comment(tb));

        while(mnt_table_next_fs(tb, itr, &fs) == 0)
                mnt_fs_print_debug(fs, stdout);

        if (mnt_table_get_trailing_comment(tb))
                fprintf(stdout, "Trailing comment:\n\"%s\"\n",
                                mnt_table_get_trailing_comment(tb));
        rc = 0;
done:
        mnt_free_iter(itr);
        mnt_unref_table(tb);
        return rc;
}

static int test_find_idx(struct libmnt_test *ts __attribute__((unused)),
                         int argc, char *argv[])
{
        struct libmnt_table *tb;
        struct libmnt_fs *fs = NULL;
        struct libmnt_cache *mpc = NULL;
        const char *file, *what;
        int rc = -1;

        if (argc != 3) {
                fprintf(stderr, "try --help\n");
                return -EINVAL;
        }

        file = argv[1], what = argv[2];

        tb = create_table(file, FALSE);
        if (!tb)
                goto done;

        /* create a cache for canonicalized paths */
        mpc = mnt_new_cache();
        if (!mpc)
                goto done;
        mnt_table_set_cache(tb, mpc);
        mnt_unref_cache(mpc);

        fs = mnt_table_find_target(tb, what, MNT_ITER_BACKWARD);

        if (!fs)
                fprintf(stderr, "%s: not found '%s'\n", file, what);
        else {
                int idx = mnt_table_find_fs(tb, fs);

                if (idx < 1)
                        fprintf(stderr, "%s: not found '%s' fs pointer", file, what);
                else {
                        printf("%s index is %d\n", what, idx);
                        rc = 0;
                }
        }
done:
        mnt_unref_table(tb);
        return rc;
}

static int test_find(struct libmnt_test *ts __attribute__((unused)),
                     int argc, char *argv[], int dr)
{
        struct libmnt_table *tb;
        struct libmnt_fs *fs = NULL;
        struct libmnt_cache *mpc = NULL;
        const char *file, *find, *what;
        int rc = -1;

        if (argc != 4) {
                fprintf(stderr, "try --help\n");
                return -EINVAL;
        }

        file = argv[1], find = argv[2], what = argv[3];

        tb = create_table(file, FALSE);
        if (!tb)
                goto done;

        /* create a cache for canonicalized paths */
        mpc = mnt_new_cache();
        if (!mpc)
                goto done;
        mnt_table_set_cache(tb, mpc);
        mnt_unref_cache(mpc);

        if (c_strcasecmp(find, "source") == 0)
                fs = mnt_table_find_source(tb, what, dr);
        else if (c_strcasecmp(find, "target") == 0)
                fs = mnt_table_find_target(tb, what, dr);

        if (!fs)
                fprintf(stderr, "%s: not found %s '%s'\n", file, find, what);
        else {
                mnt_fs_print_debug(fs, stdout);
                rc = 0;
        }
done:
        mnt_unref_table(tb);
        return rc;
}

static int test_find_bw(struct libmnt_test *ts __attribute__((unused)),
                        int argc, char *argv[])
{
        return test_find(ts, argc, argv, MNT_ITER_BACKWARD);
}

static int test_find_fw(struct libmnt_test *ts __attribute__((unused)),
                        int argc, char *argv[])
{
        return test_find(ts, argc, argv, MNT_ITER_FORWARD);
}

static int test_find_pair(struct libmnt_test *ts __attribute__((unused)),
                          int argc, char *argv[])
{
        struct libmnt_table *tb;
        struct libmnt_fs *fs;
        struct libmnt_cache *mpc = NULL;
        int rc = -1;

        if (argc != 4)
                return -1;

        tb = create_table(argv[1], FALSE);
        if (!tb)
                return -1;
        mpc = mnt_new_cache();
        if (!mpc)
                goto done;
        mnt_table_set_cache(tb, mpc);
        mnt_unref_cache(mpc);

        fs = mnt_table_find_pair(tb, argv[2], argv[3], MNT_ITER_FORWARD);
        if (!fs)
                goto done;

        mnt_fs_print_debug(fs, stdout);
        rc = 0;
done:
        mnt_unref_table(tb);
        return rc;
}

static int test_find_mountpoint(struct libmnt_test *ts __attribute__((unused)),
                                int argc, char *argv[])
{
        struct libmnt_table *tb;
        struct libmnt_fs *fs;
        struct libmnt_cache *mpc = NULL;
        int rc = -1;

        if (argc != 2)
                return -1;

        tb = mnt_new_table_from_file(_PATH_PROC_MOUNTINFO);
        if (!tb)
                return -1;
        mpc = mnt_new_cache();
        if (!mpc)
                goto done;
        mnt_table_set_cache(tb, mpc);
        mnt_unref_cache(mpc);

        fs = mnt_table_find_mountpoint(tb, argv[1], MNT_ITER_BACKWARD);
        if (!fs)
                goto done;

        mnt_fs_print_debug(fs, stdout);
        rc = 0;
done:
        mnt_unref_table(tb);
        return rc;
}

static int test_is_mounted(struct libmnt_test *ts __attribute__((unused)),
                           int argc, char *argv[])
{
        struct libmnt_table *tb = NULL, *fstab = NULL;
        struct libmnt_fs *fs;
        struct libmnt_iter *itr = NULL;
        struct libmnt_cache *mpc = NULL;

        if (argc != 2)
                return -1;

        tb = mnt_new_table_from_file("/proc/self/mountinfo");
        if (!tb) {
                fprintf(stderr, "failed to parse mountinfo\n");
                return -1;
        }

        fstab = create_table(argv[1], FALSE);
        if (!fstab)
                goto done;

        itr = mnt_new_iter(MNT_ITER_FORWARD);
        if (!itr)
                goto done;

        mpc = mnt_new_cache();
        if (!mpc)
                goto done;
        mnt_table_set_cache(tb, mpc);
        mnt_unref_cache(mpc);

        while (mnt_table_next_fs(fstab, itr, &fs) == 0) {
                if (mnt_table_is_fs_mounted(tb, fs))
                        printf("%s already mounted on %s\n",
                                        mnt_fs_get_source(fs),
                                        mnt_fs_get_target(fs));
                else
                        printf("%s not mounted on %s\n",
                                        mnt_fs_get_source(fs),
                                        mnt_fs_get_target(fs));
        }

done:
        mnt_unref_table(tb);
        mnt_unref_table(fstab);
        mnt_free_iter(itr);
        return 0;
}

/* returns 0 if @a and @b targets are the same */
static int test_uniq_cmp(struct libmnt_table *tb __attribute__((__unused__)),
                         struct libmnt_fs *a,
                         struct libmnt_fs *b)
{
        assert(a);
        assert(b);

        return mnt_fs_streq_target(a, mnt_fs_get_target(b)) ? 0 : 1;
}

static int test_uniq(struct libmnt_test *ts __attribute__((unused)),
                     int argc, char *argv[])
{
        struct libmnt_table *tb;
        int rc = -1;

        if (argc != 2) {
                fprintf(stderr, "try --help\n");
                return -EINVAL;
        }

        tb = create_table(argv[1], FALSE);
        if (!tb)
                goto done;

        if (mnt_table_uniq_fs(tb, 0, test_uniq_cmp) == 0) {
                struct libmnt_iter *itr = mnt_new_iter(MNT_ITER_FORWARD);
                struct libmnt_fs *fs;
                if (!itr)
                        goto done;
                while (mnt_table_next_fs(tb, itr, &fs) == 0)
                        mnt_fs_print_debug(fs, stdout);
                mnt_free_iter(itr);
                rc = 0;
        }
done:
        mnt_unref_table(tb);
        return rc;
}


int main(int argc, char *argv[])
{
        struct libmnt_test tss[] = {
        { "--parse",    test_parse,        "<file> [--comments] parse and print tab" },
        { "--find-forward",  test_find_fw, "<file> <source|target> <string>" },
        { "--find-backward", test_find_bw, "<file> <source|target> <string>" },
        { "--uniq-target",   test_uniq,    "<file>" },
        { "--find-pair",     test_find_pair, "<file> <source> <target>" },
        { "--find-fs",       test_find_idx, "<file> <target>" },
        { "--find-mountpoint", test_find_mountpoint, "<path>" },
        { "--copy-fs",       test_copy_fs, "<file>  copy root FS from the file" },
        { "--is-mounted",    test_is_mounted, "<fstab> check what from fstab is already mounted" },
        { NULL }
        };

        return mnt_run_test(tss, argc, argv);
}

#endif /* TEST_PROGRAM */