[thirdparty/util-linux.git] / lib / loopdev.c

/*
 * No copyright is claimed.  This code is in the public domain; do with
 * it what you wish.
 *
 * Written by Karel Zak <kzak@redhat.com>
 *
 * -- based on mount/losetup.c
 *
 * Simple library for work with loop devices.
 *
 *  - requires kernel 2.6.x
 *  - reads info from /sys/block/loop<N>/loop/<attr> (new kernels)
 *  - reads info by ioctl
 *  - supports *unlimited* number of loop devices
 *  - supports /dev/loop<N> as well as /dev/loop/<N>
 *  - minimize overhead (fd, loopinfo, ... are shared for all operations)
 *  - setup (associate device and backing file)
 *  - delete (dis-associate file)
 *  - old LOOP_{SET,GET}_STATUS (32bit) ioctls are unsupported
 *  - extendible
 */
#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <ctype.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <inttypes.h>
#include <dirent.h>

#include "linux_version.h"
#include "c.h"
#include "sysfs.h"
#include "pathnames.h"
#include "loopdev.h"
#include "canonicalize.h"
#include "blkdev.h"
#include "debug.h"
#include "fileutils.h"

#define LOOPDEV_MAX_TRIES       10

/*
 * Debug stuff (based on include/debug.h)
 */
static UL_DEBUG_DEFINE_MASK(loopdev);
UL_DEBUG_DEFINE_MASKNAMES(loopdev) = UL_DEBUG_EMPTY_MASKNAMES;

#define LOOPDEV_DEBUG_INIT      (1 << 1)
#define LOOPDEV_DEBUG_CXT       (1 << 2)
#define LOOPDEV_DEBUG_ITER      (1 << 3)
#define LOOPDEV_DEBUG_SETUP     (1 << 4)

#define DBG(m, x)       __UL_DBG(loopdev, LOOPDEV_DEBUG_, m, x)
#define ON_DBG(m, x)    __UL_DBG_CALL(loopdev, LOOPDEV_DEBUG_, m, x)

#define UL_DEBUG_CURRENT_MASK   UL_DEBUG_MASK(loopdev)
#include "debugobj.h"

static void loopdev_init_debug(void)
{
        if (loopdev_debug_mask)
                return;
        __UL_INIT_DEBUG_FROM_ENV(loopdev, LOOPDEV_DEBUG_, 0, LOOPDEV_DEBUG);
}

/*
 * see loopcxt_init()
 */
#define loopcxt_ioctl_enabled(_lc)      (!((_lc)->flags & LOOPDEV_FL_NOIOCTL))
#define loopcxt_sysfs_available(_lc)    (!((_lc)->flags & LOOPDEV_FL_NOSYSFS)) \
                                         && !loopcxt_ioctl_enabled(_lc)

/*
 * Calls @x and repeat on EAGAIN
 */
#define repeat_on_eagain(x) __extension__ ({                    \
                int _c = 0, _e;                                 \
                do {                                            \
                        errno = 0;                              \
                        _e = x;                                 \
                        if (_e == 0 || errno != EAGAIN)         \
                                break;                          \
                        if (_c >= LOOPDEV_MAX_TRIES)            \
                                break;                          \
                        xusleep(250000);                        \
                        _c++;                                   \
                } while (1);                                    \
                _e == 0 ? 0 : errno ? -errno : -1;              \
        })

/*
 * @lc: context
 * @device: device name, absolute device path or NULL to reset the current setting
 *
 * Sets device, absolute paths (e.g. "/dev/loop<N>") are unchanged, device
 * names ("loop<N>") are converted to the path (/dev/loop<N> or to
 * /dev/loop/<N>)
 *
 * This sets the device name, but does not check if the device exists!
 *
 * Returns: <0 on error, 0 on success
 */
int loopcxt_set_device(struct loopdev_cxt *lc, const char *device)
{
        if (!lc)
                return -EINVAL;

        if (lc->fd >= 0) {
                close(lc->fd);
                DBG(CXT, ul_debugobj(lc, "closing old open fd"));
        }
        lc->fd = -1;
        lc->is_lost = 0;
        lc->devno = 0;
        lc->mode = O_RDONLY;
        lc->blocksize = 0;
        lc->has_info = 0;
        lc->info_failed = 0;
        *lc->device = '\0';
        memset(&lc->config, 0, sizeof(lc->config));

        /* set new */
        if (device) {
                if (*device != '/') {
                        const char *dir = _PATH_DEV;

                        /* compose device name for /dev/loop<n> or /dev/loop/<n> */
                        if (lc->flags & LOOPDEV_FL_DEVSUBDIR) {
                                if (strlen(device) < 5)
                                        return -1;
                                device += 4;
                                dir = _PATH_DEV_LOOP "/";       /* _PATH_DEV uses trailing slash */
                        }
                        snprintf(lc->device, sizeof(lc->device), "%s%s",
                                dir, device);
                } else
                        xstrncpy(lc->device, device, sizeof(lc->device));

                DBG(CXT, ul_debugobj(lc, "%s name assigned", device));
        }

        ul_unref_path(lc->sysfs);
        lc->sysfs = NULL;
        return 0;
}

int loopcxt_has_device(struct loopdev_cxt *lc)
{
        return lc && *lc->device;
}

dev_t loopcxt_get_devno(struct loopdev_cxt *lc)
{
        if (!lc || !loopcxt_has_device(lc))
                return 0;
        if (!lc->devno)
                lc->devno = sysfs_devname_to_devno(lc->device);
        return lc->devno;
}

int loopcxt_is_lost(struct loopdev_cxt *lc)
{
        if (!lc || !loopcxt_has_device(lc))
                return 0;
        if (lc->is_lost)
                return 1;

        lc->is_lost = access(lc->device, F_OK) != 0
                        && loopcxt_get_devno(lc) != 0;

        return lc->is_lost;
}

/*
 * @lc: context
 * @flags: LOOPDEV_FL_* flags
 *
 * Initialize loop handler.
 *
 * We have two sets of the flags:
 *
 *      * LOOPDEV_FL_* flags control loopcxt_* API behavior
 *
 *      * LO_FLAGS_* are kernel flags used for LOOP_{SET,GET}_STAT64 ioctls
 *
 * Returns: <0 on error, 0 on success.
 */
int loopcxt_init(struct loopdev_cxt *lc, int flags)
{
        int rc;
        struct stat st;
        struct loopdev_cxt dummy = UL_LOOPDEVCXT_EMPTY;

        if (!lc)
                return -EINVAL;

        loopdev_init_debug();
        DBG(CXT, ul_debugobj(lc, "initialize context"));

        memcpy(lc, &dummy, sizeof(dummy));
        lc->flags = flags;

        rc = loopcxt_set_device(lc, NULL);
        if (rc)
                return rc;

        if (stat(_PATH_SYS_BLOCK, &st) || !S_ISDIR(st.st_mode)) {
                lc->flags |= LOOPDEV_FL_NOSYSFS;
                lc->flags &= ~LOOPDEV_FL_NOIOCTL;
                DBG(CXT, ul_debugobj(lc, "init: disable /sys usage"));
        }

        if (!(lc->flags & LOOPDEV_FL_NOSYSFS) &&
            get_linux_version() >= KERNEL_VERSION(2,6,37)) {
                /*
                 * Use only sysfs for basic information about loop devices
                 */
                lc->flags |= LOOPDEV_FL_NOIOCTL;
                DBG(CXT, ul_debugobj(lc, "init: ignore ioctls"));
        }

        if (!(lc->flags & LOOPDEV_FL_CONTROL) && !stat(_PATH_DEV_LOOPCTL, &st)) {
                lc->flags |= LOOPDEV_FL_CONTROL;
                DBG(CXT, ul_debugobj(lc, "init: loop-control detected "));
        }

        return 0;
}

/*
 * @lc: context
 *
 * Deinitialize loop context
 */
void loopcxt_deinit(struct loopdev_cxt *lc)
{
        int errsv = errno;

        if (!lc)
                return;

        DBG(CXT, ul_debugobj(lc, "de-initialize"));

        free(lc->filename);
        lc->filename = NULL;

        ignore_result( loopcxt_set_device(lc, NULL) );
        loopcxt_deinit_iterator(lc);

        errno = errsv;
}

/*
 * @lc: context
 *
 * Returns newly allocated device path.
 */
char *loopcxt_strdup_device(struct loopdev_cxt *lc)
{
        if (!lc || !*lc->device)
                return NULL;
        return strdup(lc->device);
}

/*
 * @lc: context
 *
 * Returns pointer device name in the @lc struct.
 */
const char *loopcxt_get_device(struct loopdev_cxt *lc)
{
        return lc && *lc->device ? lc->device : NULL;
}

/*
 * @lc: context
 *
 * Returns pointer to the sysfs context (see lib/sysfs.c)
 */
static struct path_cxt *loopcxt_get_sysfs(struct loopdev_cxt *lc)
{
        if (!lc || !*lc->device || (lc->flags & LOOPDEV_FL_NOSYSFS))
                return NULL;

        if (!lc->sysfs) {
                dev_t devno = loopcxt_get_devno(lc);
                if (!devno) {
                        DBG(CXT, ul_debugobj(lc, "sysfs: failed devname to devno"));
                        return NULL;
                }

                lc->sysfs = ul_new_sysfs_path(devno, NULL, NULL);
                if (!lc->sysfs)
                        DBG(CXT, ul_debugobj(lc, "sysfs: init failed"));
        }

        return lc->sysfs;
}

static int __loopcxt_get_fd(struct loopdev_cxt *lc, mode_t mode)
{
        int old = -1;

        if (!lc || !*lc->device)
                return -EINVAL;

        /* It's okay to return a FD with read-write permissions if someone
         * asked for read-only, but you shouldn't do the opposite.
         *
         * (O_RDONLY is a widely usable default.)
         */
        if (lc->fd >= 0 && mode == O_RDWR && lc->mode == O_RDONLY) {
                DBG(CXT, ul_debugobj(lc, "closing already open device (mode mismatch)"));
                old = lc->fd;
                lc->fd = -1;
        }

        if (lc->fd < 0) {
                lc->mode = mode;
                lc->fd = open(lc->device, lc->mode | O_CLOEXEC);
                DBG(CXT, ul_debugobj(lc, "open %s [%s]: %m", lc->device,
                                mode == O_RDONLY ? "ro" :
                                mode == O_RDWR ? "rw" : "??"));

                if (lc->fd < 0 && old >= 0) {
                        /* restore original on error */
                        lc->fd = old;
                        old = -1;
                }
        }

        if (old >= 0)
                close(old);
        return lc->fd;
}

/* default is read-only file descriptor, it's enough for all ioctls */
int loopcxt_get_fd(struct loopdev_cxt *lc)
{
        return __loopcxt_get_fd(lc, O_RDONLY);
}

/*
 * @lc: context
 * @flags: LOOPITER_FL_* flags
 *
 * Iterator can be used to scan list of the free or used loop devices.
 *
 * Returns: <0 on error, 0 on success
 */
int loopcxt_init_iterator(struct loopdev_cxt *lc, int flags)
{
        struct loopdev_iter *iter;
        struct stat st;

        if (!lc)
                return -EINVAL;


        iter = &lc->iter;
        DBG(ITER, ul_debugobj(iter, "initialize"));

        /* always zeroize
         */
        memset(iter, 0, sizeof(*iter));
        iter->ncur = -1;
        iter->flags = flags;
        iter->default_check = 1;

        if (!lc->extra_check) {
                /*
                 * Check for /dev/loop/<N> subdirectory
                 */
                if (!(lc->flags & LOOPDEV_FL_DEVSUBDIR) &&
                    stat(_PATH_DEV_LOOP, &st) == 0 && S_ISDIR(st.st_mode))
                        lc->flags |= LOOPDEV_FL_DEVSUBDIR;

                lc->extra_check = 1;
        }
        return 0;
}

/*
 * @lc: context
 *
 * Returns: <0 on error, 0 on success
 */
int loopcxt_deinit_iterator(struct loopdev_cxt *lc)
{
        struct loopdev_iter *iter;

        if (!lc)
                return -EINVAL;

        iter = &lc->iter;
        DBG(ITER, ul_debugobj(iter, "de-initialize"));

        free(iter->minors);
        if (iter->proc)
                fclose(iter->proc);
        if (iter->sysblock)
                closedir(iter->sysblock);

        memset(iter, 0, sizeof(*iter));
        return 0;
}

/*
 * Same as loopcxt_set_device, but also checks if the device is
 * associated with any file.
 *
 * Returns: <0 on error, 0 on success, 1 device does not match with
 *         LOOPITER_FL_{USED,FREE} flags.
 */
static int loopiter_set_device(struct loopdev_cxt *lc, const char *device)
{
        int rc = loopcxt_set_device(lc, device);
        int used;

        if (rc)
                return rc;

        if (!(lc->iter.flags & LOOPITER_FL_USED) &&
            !(lc->iter.flags & LOOPITER_FL_FREE))
                return 0;       /* caller does not care about device status */

        used = loopcxt_get_offset(lc, NULL) == 0;

        if ((lc->iter.flags & LOOPITER_FL_USED) && used)
                return 0;

        if ((lc->iter.flags & LOOPITER_FL_FREE) && !used)
                return 0;

        DBG(ITER, ul_debugobj(&lc->iter, "failed to use %s device", lc->device));

        ignore_result( loopcxt_set_device(lc, NULL) );
        return 1;
}

static int cmpnum(const void *p1, const void *p2)
{
        return (((* (const int *) p1) > (* (const int *) p2)) -
                        ((* (const int *) p1) < (* (const int *) p2)));
}

/*
 * The classic scandir() is more expensive and less portable.
 * We needn't full loop device names -- loop numbers (loop<N>)
 * are enough.
 */
static int loop_scandir(const char *dirname, int **ary, int hasprefix)
{
        DIR *dir;
        struct dirent *d;
        unsigned int n, count = 0, arylen = 0;

        if (!dirname || !ary)
                return 0;

        DBG(ITER, ul_debug("scan dir: %s", dirname));

        dir = opendir(dirname);
        if (!dir)
                return 0;
        free(*ary);
        *ary = NULL;

        while((d = readdir(dir))) {
#ifdef _DIRENT_HAVE_D_TYPE
                if (d->d_type != DT_BLK && d->d_type != DT_UNKNOWN &&
                    d->d_type != DT_LNK)
                        continue;
#endif
                if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, ".."))
                        continue;

                if (hasprefix) {
                        /* /dev/loop<N> */
                        if (sscanf(d->d_name, "loop%u", &n) != 1)
                                continue;
                } else {
                        /* /dev/loop/<N> */
                        char *end = NULL;

                        errno = 0;
                        n = strtol(d->d_name, &end, 10);
                        if (d->d_name == end || (end && *end) || errno)
                                continue;
                }
                if (n < LOOPDEV_DEFAULT_NNODES)
                        continue;                       /* ignore loop<0..7> */

                if (count + 1 > arylen) {
                        int *tmp;

                        arylen += 1;

                        tmp = reallocarray(*ary, arylen, sizeof(int));
                        if (!tmp) {
                                free(*ary);
                                *ary = NULL;
                                closedir(dir);
                                return -1;
                        }
                        *ary = tmp;
                }
                if (*ary)
                        (*ary)[count++] = n;
        }
        if (count && *ary)
                qsort(*ary, count, sizeof(int), cmpnum);

        closedir(dir);
        return count;
}

/*
 * Set the next *used* loop device according to /proc/partitions.
 *
 * Loop devices smaller than 512 bytes are invisible for this function.
 */
static int loopcxt_next_from_proc(struct loopdev_cxt *lc)
{
        struct loopdev_iter *iter = &lc->iter;
        char buf[BUFSIZ];

        DBG(ITER, ul_debugobj(iter, "scan /proc/partitions"));

        if (!iter->proc)
                iter->proc = fopen(_PATH_PROC_PARTITIONS, "r" UL_CLOEXECSTR);
        if (!iter->proc)
                return 1;

        while (fgets(buf, sizeof(buf), iter->proc)) {
                unsigned int m;
                char name[128 + 1];


                if (sscanf(buf, " %u %*s %*s %128[^\n ]",
                           &m, name) != 2 || m != LOOPDEV_MAJOR)
                        continue;

                DBG(ITER, ul_debugobj(iter, "checking %s", name));

                if (loopiter_set_device(lc, name) == 0)
                        return 0;
        }

        return 1;
}

/*
 * Set the next *used* loop device according to
 * /sys/block/loopN/loop/backing_file (kernel >= 2.6.37 is required).
 *
 * This is preferred method.
 */
static int loopcxt_next_from_sysfs(struct loopdev_cxt *lc)
{
        struct loopdev_iter *iter = &lc->iter;
        struct dirent *d;
        int fd;

        DBG(ITER, ul_debugobj(iter, "scanning /sys/block"));

        if (!iter->sysblock)
                iter->sysblock = opendir(_PATH_SYS_BLOCK);

        if (!iter->sysblock)
                return 1;

        fd = dirfd(iter->sysblock);

        while ((d = readdir(iter->sysblock))) {
                char name[NAME_MAX + 18 + 1];
                struct stat st;

                DBG(ITER, ul_debugobj(iter, "check %s", d->d_name));

                if (strcmp(d->d_name, ".") == 0
                    || strcmp(d->d_name, "..") == 0
                    || strncmp(d->d_name, "loop", 4) != 0)
                        continue;

                snprintf(name, sizeof(name), "%s/loop/backing_file", d->d_name);
                if (fstatat(fd, name, &st, 0) != 0)
                        continue;

                if (loopiter_set_device(lc, d->d_name) == 0)
                        return 0;
        }

        return 1;
}

/*
 * @lc: context, has to initialized by loopcxt_init_iterator()
 *
 * Returns: 0 on success, < 0 on error, 1 at the end of scanning. The details
 *          about the current loop device are available by
 *          loopcxt_get_{fd,backing_file,device,offset, ...} functions.
 */
int loopcxt_next(struct loopdev_cxt *lc)
{
        struct loopdev_iter *iter;

        if (!lc)
                return -EINVAL;


        iter = &lc->iter;
        if (iter->done)
                return 1;

        DBG(ITER, ul_debugobj(iter, "next"));

        /* A) Look for used loop devices in /proc/partitions ("losetup -a" only)
         */
        if (iter->flags & LOOPITER_FL_USED) {
                int rc;

                if (loopcxt_sysfs_available(lc))
                        rc = loopcxt_next_from_sysfs(lc);
                else
                        rc = loopcxt_next_from_proc(lc);
                if (rc == 0)
                        return 0;
                goto done;
        }

        /* B) Classic way, try first eight loop devices (default number
         *    of loop devices). This is enough for 99% of all cases.
         */
        if (iter->default_check) {
                DBG(ITER, ul_debugobj(iter, "next: default check"));
                for (++iter->ncur; iter->ncur < LOOPDEV_DEFAULT_NNODES;
                                                        iter->ncur++) {
                        char name[16];
                        snprintf(name, sizeof(name), "loop%d", iter->ncur);

                        if (loopiter_set_device(lc, name) == 0)
                                return 0;
                }
                iter->default_check = 0;
        }

        /* C) the worst possibility, scan whole /dev or /dev/loop/<N>
         */
        if (!iter->minors) {
                DBG(ITER, ul_debugobj(iter, "next: scanning /dev"));
                iter->nminors = (lc->flags & LOOPDEV_FL_DEVSUBDIR) ?
                        loop_scandir(_PATH_DEV_LOOP, &iter->minors, 0) :
                        loop_scandir(_PATH_DEV, &iter->minors, 1);
                iter->ncur = -1;
        }
        for (++iter->ncur; iter->ncur < iter->nminors; iter->ncur++) {
                char name[16];
                snprintf(name, sizeof(name), "loop%d", iter->minors[iter->ncur]);

                if (loopiter_set_device(lc, name) == 0)
                        return 0;
        }
done:
        loopcxt_deinit_iterator(lc);
        return 1;
}

/*
 * @device: path to device
 */
int is_loopdev(const char *device)
{
        struct stat st;
        int rc = 0;

        if (!device || stat(device, &st) != 0 || !S_ISBLK(st.st_mode))
                rc = 0;
        else if (major(st.st_rdev) == LOOPDEV_MAJOR)
                rc = 1;
        else if (sysfs_devno_is_wholedisk(st.st_rdev)) {
                /* It's possible that kernel creates a device with a different
                 * major number ... check by /sys it's really loop device.
                 */
                char name[PATH_MAX], *cn, *p = NULL;

                snprintf(name, sizeof(name), _PATH_SYS_DEVBLOCK "/%d:%d",
                                major(st.st_rdev), minor(st.st_rdev));
                cn = canonicalize_path(name);
                if (cn)
                        p = stripoff_last_component(cn);
                rc = p && ul_startswith(p, "loop");
                free(cn);
        }

        if (rc == 0)
                errno = ENODEV;
        return rc;
}

/*
 * @lc: context
 *
 * Returns result from LOOP_GET_STAT64 ioctl or NULL on error.
 */
struct loop_info64 *loopcxt_get_info(struct loopdev_cxt *lc)
{
        int fd;

        if (!lc || lc->info_failed) {
                errno = EINVAL;
                return NULL;
        }
        errno = 0;
        if (lc->has_info)
                return &lc->config.info;

        fd = loopcxt_get_fd(lc);
        if (fd < 0)
                return NULL;

        if (ioctl(fd, LOOP_GET_STATUS64, &lc->config.info) == 0) {
                lc->has_info = 1;
                lc->info_failed = 0;
                DBG(CXT, ul_debugobj(lc, "reading loop_info64 OK"));
                return &lc->config.info;
        }

        lc->info_failed = 1;
        DBG(CXT, ul_debugobj(lc, "reading loop_info64 FAILED"));

        return NULL;
}

/*
 * @lc: context
 *
 * Returns (allocated) string with path to the file associated
 * with the current loop device.
 */
char *loopcxt_get_backing_file(struct loopdev_cxt *lc)
{
        struct path_cxt *sysfs = loopcxt_get_sysfs(lc);
        char *res = NULL;

        if (sysfs)
                /*
                 * This is always preferred, the loop_info64
                 * has too small buffer for the filename.
                 */
                ul_path_read_string(sysfs, &res, "loop/backing_file");

        if (!res && loopcxt_ioctl_enabled(lc)) {
                struct loop_info64 *lo = loopcxt_get_info(lc);

                if (lo) {
                        lo->lo_file_name[LO_NAME_SIZE - 2] = '*';
                        lo->lo_file_name[LO_NAME_SIZE - 1] = '\0';
                        res = strdup((char *) lo->lo_file_name);
                }
        }

        DBG(CXT, ul_debugobj(lc, "get_backing_file [%s]", res));
        return res;
}

/*
 * @lc: context
 *
 * Returns (allocated) string with loop reference. The same as backing file by
 * default.
 */
char *loopcxt_get_refname(struct loopdev_cxt *lc)
{
        char *res = NULL;
        struct loop_info64 *lo = loopcxt_get_info(lc);

        if (lo) {
                lo->lo_file_name[LO_NAME_SIZE - 1] = '\0';
                res = strdup((char *) lo->lo_file_name);
        }

        DBG(CXT, ul_debugobj(lc, "get_refname [%s]", res));
        return res;
}

/*
 * @lc: context
 * @offset: returns offset number for the given device
 *
 * Returns: <0 on error, 0 on success
 */
int loopcxt_get_offset(struct loopdev_cxt *lc, uint64_t *offset)
{
        struct path_cxt *sysfs = loopcxt_get_sysfs(lc);
        int rc = -EINVAL;

        if (sysfs)
                if (ul_path_read_u64(sysfs, offset, "loop/offset") == 0)
                        rc = 0;

        if (rc && loopcxt_ioctl_enabled(lc)) {
                struct loop_info64 *lo = loopcxt_get_info(lc);
                if (lo) {
                        if (offset)
                                *offset = lo->lo_offset;
                        rc = 0;
                } else
                        rc = -errno;
        }

        DBG(CXT, ul_debugobj(lc, "get_offset [rc=%d]", rc));
        return rc;
}

/*
 * @lc: context
 * @blocksize: returns logical blocksize for the given device
 *
 * Returns: <0 on error, 0 on success
 */
int loopcxt_get_blocksize(struct loopdev_cxt *lc, uint64_t *blocksize)
{
        struct path_cxt *sysfs = loopcxt_get_sysfs(lc);
        int rc = -EINVAL;

        if (sysfs)
                if (ul_path_read_u64(sysfs, blocksize, "queue/logical_block_size") == 0)
                        rc = 0;

        /* Fallback based on BLKSSZGET ioctl */
        if (rc) {
                int fd = loopcxt_get_fd(lc);
                int sz = 0;

                if (fd < 0)
                        return -EINVAL;
                rc = blkdev_get_sector_size(fd, &sz);
                if (rc)
                        return rc;

                *blocksize = sz;
        }

        DBG(CXT, ul_debugobj(lc, "get_blocksize [rc=%d]", rc));
        return rc;
}

/*
 * @lc: context
 * @sizelimit: returns size limit for the given device
 *
 * Returns: <0 on error, 0 on success
 */
int loopcxt_get_sizelimit(struct loopdev_cxt *lc, uint64_t *size)
{
        struct path_cxt *sysfs = loopcxt_get_sysfs(lc);
        int rc = -EINVAL;

        if (sysfs)
                if (ul_path_read_u64(sysfs, size, "loop/sizelimit") == 0)
                        rc = 0;

        if (rc && loopcxt_ioctl_enabled(lc)) {
                struct loop_info64 *lo = loopcxt_get_info(lc);
                if (lo) {
                        if (size)
                                *size = lo->lo_sizelimit;
                        rc = 0;
                } else
                        rc = -errno;
        }

        DBG(CXT, ul_debugobj(lc, "get_sizelimit [rc=%d]", rc));
        return rc;
}

/*
 * @lc: context
 * @type: returns encryption type
 *
 * Cryptoloop is DEPRECATED!
 *
 * Returns: <0 on error, 0 on success
 */
int loopcxt_get_encrypt_type(struct loopdev_cxt *lc, uint32_t *type)
{
        struct loop_info64 *lo = loopcxt_get_info(lc);
        int rc;

        /* not provided by sysfs */
        if (lo) {
                if (type)
                        *type = lo->lo_encrypt_type;
                rc = 0;
        } else
                rc = -errno;

        DBG(CXT, ul_debugobj(lc, "get_encrypt_type [rc=%d]", rc));
        return rc;
}

/*
 * @lc: context
 *
 * Cryptoloop is DEPRECATED!
 *
 * Returns: <0 on error, 0 on success
 */
const char *loopcxt_get_crypt_name(struct loopdev_cxt *lc)
{
        struct loop_info64 *lo = loopcxt_get_info(lc);

        if (lo)
                return (char *) lo->lo_crypt_name;

        DBG(CXT, ul_debugobj(lc, "get_crypt_name failed"));
        return NULL;
}

/*
 * @lc: context
 * @devno: returns backing file devno
 *
 * Returns: <0 on error, 0 on success
 */
int loopcxt_get_backing_devno(struct loopdev_cxt *lc, dev_t *devno)
{
        struct loop_info64 *lo = loopcxt_get_info(lc);
        int rc;

        if (lo) {
                if (devno)
                        *devno = lo->lo_device;
                rc = 0;
        } else
                rc = -errno;

        DBG(CXT, ul_debugobj(lc, "get_backing_devno [rc=%d]", rc));
        return rc;
}

/*
 * @lc: context
 * @ino: returns backing file inode
 *
 * Returns: <0 on error, 0 on success
 */
int loopcxt_get_backing_inode(struct loopdev_cxt *lc, ino_t *ino)
{
        struct loop_info64 *lo = loopcxt_get_info(lc);
        int rc;

        if (lo) {
                if (ino)
                        *ino = lo->lo_inode;
                rc = 0;
        } else
                rc = -errno;

        DBG(CXT, ul_debugobj(lc, "get_backing_inode [rc=%d]", rc));
        return rc;
}

/*
 * Check if the kernel supports partitioned loop devices.
 *
 * Notes:
 *   - kernels < 3.2 support partitioned loop devices and PT scanning
 *     only if max_part= module parameter is non-zero
 *
 *   - kernels >= 3.2 always support partitioned loop devices
 *
 *   - kernels >= 3.2 always support BLKPG_{ADD,DEL}_PARTITION ioctls
 *
 *   - kernels >= 3.2 enable PT scanner only if max_part= is non-zero or if the
 *     LO_FLAGS_PARTSCAN flag is set for the device. The PT scanner is disabled
 *     by default.
 *
 *  See kernel commit e03c8dd14915fabc101aa495828d58598dc5af98.
 */
int loopmod_supports_partscan(void)
{
        int rc, ret = 0;
        FILE *f;

        if (get_linux_version() >= KERNEL_VERSION(3,2,0))
                return 1;

        f = fopen("/sys/module/loop/parameters/max_part", "r" UL_CLOEXECSTR);
        if (!f)
                return 0;
        rc = fscanf(f, "%d", &ret);
        fclose(f);
        return rc == 1 ? ret : 0;
}

/*
 * @lc: context
 *
 * Returns: 1 if the partscan flags is set *or* (for old kernels) partitions
 * scanning is enabled for all loop devices.
 */
int loopcxt_is_partscan(struct loopdev_cxt *lc)
{
        struct path_cxt *sysfs = loopcxt_get_sysfs(lc);

        if (sysfs) {
                /* kernel >= 3.2 */
                int fl;
                if (ul_path_read_s32(sysfs, &fl, "loop/partscan") == 0)
                        return fl;
        }

        /* old kernels (including kernels without loopN/loop/<flags> directory */
        return loopmod_supports_partscan();
}

/*
 * @lc: context
 *
 * Returns: 1 if the autoclear flags is set.
 */
int loopcxt_is_autoclear(struct loopdev_cxt *lc)
{
        struct path_cxt *sysfs = loopcxt_get_sysfs(lc);

        if (sysfs) {
                int fl;
                if (ul_path_read_s32(sysfs, &fl, "loop/autoclear") == 0)
                        return fl;
        }

        if (loopcxt_ioctl_enabled(lc)) {
                struct loop_info64 *lo = loopcxt_get_info(lc);
                if (lo)
                        return lo->lo_flags & LO_FLAGS_AUTOCLEAR;
        }
        return 0;
}

/*
 * @lc: context
 *
 * Returns: 1 if the readonly flags is set.
 */
int loopcxt_is_readonly(struct loopdev_cxt *lc)
{
        struct path_cxt *sysfs = loopcxt_get_sysfs(lc);

        if (sysfs) {
                int fl;
                if (ul_path_read_s32(sysfs, &fl, "ro") == 0)
                        return fl;
        }

        if (loopcxt_ioctl_enabled(lc)) {
                struct loop_info64 *lo = loopcxt_get_info(lc);
                if (lo)
                        return lo->lo_flags & LO_FLAGS_READ_ONLY;
        }
        return 0;
}

/*
 * @lc: context
 *
 * Returns: 1 if the dio flags is set.
 */
int loopcxt_is_dio(struct loopdev_cxt *lc)
{
        struct path_cxt *sysfs = loopcxt_get_sysfs(lc);

        if (sysfs) {
                int fl;
                if (ul_path_read_s32(sysfs, &fl, "loop/dio") == 0)
                        return fl;
        }
        if (loopcxt_ioctl_enabled(lc)) {
                struct loop_info64 *lo = loopcxt_get_info(lc);
                if (lo)
                        return lo->lo_flags & LO_FLAGS_DIRECT_IO;
        }
        return 0;
}

/*
 * @lc: context
 * @st: backing file stat or NULL
 * @backing_file: filename
 * @offset: offset (use LOOPDEV_FL_OFFSET if specified)
 * @sizelimit: size limit (use LOOPDEV_FL_SIZELIMIT if specified)
 * @flags: LOOPDEV_FL_{OFFSET,SIZELIMIT}
 *
 * Returns 1 if the current @lc loopdev is associated with the given backing
 * file. Note that the preferred way is to use devno and inode number rather
 * than filename. The @backing_file filename is poor solution usable in case
 * that you don't have rights to call stat().
 *
 * LOOPDEV_FL_SIZELIMIT requires LOOPDEV_FL_OFFSET being set as well.
 *
 * Don't forget that old kernels provide very restricted (in size) backing
 * filename by LOOP_GET_STAT64 ioctl only.
 */
int loopcxt_is_used(struct loopdev_cxt *lc,
                    struct stat *st,
                    const char *backing_file,
                    uint64_t offset,
                    uint64_t sizelimit,
                    int flags)
{
        ino_t ino = 0;
        dev_t dev = 0;

        if (!lc)
                return 0;

        DBG(CXT, ul_debugobj(lc, "checking %s vs. %s",
                                loopcxt_get_device(lc),
                                backing_file));

        if (st && loopcxt_get_backing_inode(lc, &ino) == 0 &&
                  loopcxt_get_backing_devno(lc, &dev) == 0) {

                if (ino == st->st_ino && dev == st->st_dev)
                        goto found;

                /* don't use filename if we have devno and inode */
                return 0;
        }

        /* poor man's solution */
        if (backing_file) {
                char *name = loopcxt_get_backing_file(lc);
                int rc = name && strcmp(name, backing_file) == 0;

                free(name);
                if (rc)
                        goto found;
        }

        return 0;
found:
        if (flags & LOOPDEV_FL_OFFSET) {
                uint64_t off = 0;

                int rc = loopcxt_get_offset(lc, &off) == 0 && off == offset;

                if (rc && flags & LOOPDEV_FL_SIZELIMIT) {
                        uint64_t sz = 0;

                        return loopcxt_get_sizelimit(lc, &sz) == 0 && sz == sizelimit;
                }
                return rc;
        }
        return 1;
}

/*
 * The setting is removed by loopcxt_set_device() loopcxt_next()!
 */
int loopcxt_set_offset(struct loopdev_cxt *lc, uint64_t offset)
{
        if (!lc)
                return -EINVAL;
        lc->config.info.lo_offset = offset;

        DBG(CXT, ul_debugobj(lc, "set offset=%jd", offset));
        return 0;
}

/*
 * The setting is removed by loopcxt_set_device() loopcxt_next()!
 */
int loopcxt_set_sizelimit(struct loopdev_cxt *lc, uint64_t sizelimit)
{
        if (!lc)
                return -EINVAL;
        lc->config.info.lo_sizelimit = sizelimit;

        DBG(CXT, ul_debugobj(lc, "set sizelimit=%jd", sizelimit));
        return 0;
}

/*
 * The blocksize will be used by loopcxt_set_device(). For already exiting
 * devices use  loopcxt_ioctl_blocksize().
 *
 * The setting is removed by loopcxt_set_device() loopcxt_next()!
 */
int loopcxt_set_blocksize(struct loopdev_cxt *lc, uint64_t blocksize)
{
        if (!lc)
                return -EINVAL;
        lc->blocksize = blocksize;

        DBG(CXT, ul_debugobj(lc, "set blocksize=%jd", blocksize));
        return 0;
}

/*
 * @lc: context
 * @flags: kernel LO_FLAGS_{READ_ONLY,USE_AOPS,AUTOCLEAR} flags
 *
 * The setting is removed by loopcxt_set_device() loopcxt_next()!
 *
 * Returns: 0 on success, <0 on error.
 */
int loopcxt_set_flags(struct loopdev_cxt *lc, uint32_t flags)
{
        if (!lc)
                return -EINVAL;
        lc->config.info.lo_flags = flags;

        DBG(CXT, ul_debugobj(lc, "set flags=%u", (unsigned) flags));
        return 0;
}

/*
 * @lc: context
 * @refname: reference name (used to overwrite lo_file_name where is backing
 *           file by default)
 *
 * The setting is removed by loopcxt_set_device() loopcxt_next()!
 *
 * Returns: 0 on success, <0 on error.
 */
int loopcxt_set_refname(struct loopdev_cxt *lc, const char *refname)
{
        if (!lc)
                return -EINVAL;

        memset(lc->config.info.lo_file_name, 0, sizeof(lc->config.info.lo_file_name));
        if (refname)
                xstrncpy((char *)lc->config.info.lo_file_name, refname, LO_NAME_SIZE);

        DBG(CXT, ul_debugobj(lc, "set refname=%s", (char *)lc->config.info.lo_file_name));
        return 0;
}

/*
 * @lc: context
 * @filename: backing file path (the path will be canonicalized)
 *
 * The setting is removed by loopcxt_set_device() loopcxt_next()!
 *
 * Returns: 0 on success, <0 on error.
 */
int loopcxt_set_backing_file(struct loopdev_cxt *lc, const char *filename)
{
        if (!lc)
                return -EINVAL;

        lc->filename = canonicalize_path(filename);
        if (!lc->filename)
                return -errno;

        if (!lc->config.info.lo_file_name[0])
                loopcxt_set_refname(lc, lc->filename);

        DBG(CXT, ul_debugobj(lc, "set backing file=%s", lc->filename));
        return 0;
}

/*
 * In kernels prior to v3.9, if the offset or sizelimit options
 * are used, the block device's size won't be synced automatically.
 * blockdev --getsize64 and filesystems will use the backing
 * file size until the block device has been re-opened or the
 * LOOP_SET_CAPACITY ioctl is called to sync the sizes.
 *
 * Since mount -oloop uses the LO_FLAGS_AUTOCLEAR option and passes
 * the open file descriptor to the mount system call, we need to use
 * the ioctl. Calling losetup directly doesn't have this problem since
 * it closes the device when it exits and whatever consumes the device
 * next will re-open it, causing the resync.
 */
static int loopcxt_check_size(struct loopdev_cxt *lc, int file_fd)
{
        uint64_t size, expected_size;
        int dev_fd;
        struct stat st;

        if (!lc->config.info.lo_offset && !lc->config.info.lo_sizelimit)
                return 0;

        if (fstat(file_fd, &st)) {
                DBG(CXT, ul_debugobj(lc, "failed to fstat backing file"));
                return -errno;
        }
        if (S_ISBLK(st.st_mode)) {
                if (blkdev_get_size(file_fd,
                                (unsigned long long *) &expected_size)) {
                        DBG(CXT, ul_debugobj(lc, "failed to determine device size"));
                        return -errno;
                }
        } else
                expected_size = st.st_size;

        if (expected_size == 0 || expected_size <= lc->config.info.lo_offset) {
                DBG(CXT, ul_debugobj(lc, "failed to determine expected size"));
                return 0;       /* ignore this error */
        }

        if (lc->config.info.lo_offset > 0)
                expected_size -= lc->config.info.lo_offset;

        if (lc->config.info.lo_sizelimit > 0 && lc->config.info.lo_sizelimit < expected_size)
                expected_size = lc->config.info.lo_sizelimit;

        dev_fd = loopcxt_get_fd(lc);
        if (dev_fd < 0) {
                DBG(CXT, ul_debugobj(lc, "failed to get loop FD"));
                return -errno;
        }

        if (blkdev_get_size(dev_fd, (unsigned long long *) &size)) {
                DBG(CXT, ul_debugobj(lc, "failed to determine loopdev size"));
                return -errno;
        }

        /* It's block device, so, align to 512-byte sectors */
        if (expected_size % 512) {
                DBG(CXT, ul_debugobj(lc, "expected size misaligned to 512-byte sectors"));
                expected_size = (expected_size >> 9) << 9;
        }

        if (expected_size != size) {
                DBG(CXT, ul_debugobj(lc, "warning: loopdev and expected "
                                      "size mismatch (%ju/%ju)",
                                      size, expected_size));

                if (loopcxt_ioctl_capacity(lc)) {
                        /* ioctl not available */
                        if (errno == ENOTTY || errno == EINVAL)
                                errno = ERANGE;
                        return -errno;
                }

                if (blkdev_get_size(dev_fd, (unsigned long long *) &size))
                        return -errno;

                if (expected_size != size) {
                        errno = ERANGE;
                        DBG(CXT, ul_debugobj(lc, "failed to set loopdev size, "
                                        "size: %ju, expected: %ju",
                                        size, expected_size));
                        return -errno;
                }
        }

        return 0;
}


/*
 * @lc: context
 *
 * Associate the current device (see loopcxt_{set,get}_device()) with
 * a file (see loopcxt_set_backing_file()).
 *
 * The device is initialized read-write by default. If you want read-only
 * device then set LO_FLAGS_READ_ONLY by loopcxt_set_flags(). The LOOPDEV_FL_*
 * flags are ignored and modified according to LO_FLAGS_*.
 *
 * If the device is already open by loopcxt_get_fd() then this setup device
 * function will re-open the device to fix read/write mode.
 *
 * The device is also initialized read-only if the backing file is not
 * possible to open read-write (e.g. read-only FS).
 *
 * Returns: <0 on error, 0 on success.
 */
int loopcxt_setup_device(struct loopdev_cxt *lc)
{
        int file_fd, dev_fd;
        mode_t flags = O_CLOEXEC, mode = O_RDWR;
        int rc = -1, cnt = 0;
        int errsv = 0;
        int fallback = 0;

        if (!lc || !*lc->device || !lc->filename)
                return -EINVAL;

        DBG(SETUP, ul_debugobj(lc, "device setup requested"));

        /*
         * Open backing file and device
         */
        if (lc->config.info.lo_flags & LO_FLAGS_READ_ONLY)
                mode = O_RDONLY;

        if (lc->config.info.lo_flags & LO_FLAGS_DIRECT_IO)
                flags |= O_DIRECT;

        if ((file_fd = open(lc->filename, mode | flags)) < 0) {
                if (mode != O_RDONLY && (errno == EROFS || errno == EACCES))
                        file_fd = open(lc->filename, (mode = O_RDONLY) | flags);

                if (file_fd < 0) {
                        DBG(SETUP, ul_debugobj(lc, "open backing file failed: %m"));
                        return -errno;
                }
        }
        DBG(SETUP, ul_debugobj(lc, "backing file open: OK"));

        if (mode == O_RDONLY)
                lc->config.info.lo_flags |= LO_FLAGS_READ_ONLY; /* kernel loopdev mode */
        else
                lc->config.info.lo_flags &= ~LO_FLAGS_READ_ONLY;

        do {
                errno = 0;

                dev_fd = __loopcxt_get_fd(lc, mode);
                if (dev_fd >= 0 || lc->control_ok == 0)
                        break;
                if (errno != EACCES && errno != ENOENT)
                        break;
                /* We have permissions to open /dev/loop-control, but open
                 * /dev/loopN failed with EACCES, it's probably because udevd
                 * does not applied chown yet. Let's wait a moment. */
                xusleep(25000);
        } while (cnt++ < 16);

        if (dev_fd < 0) {
                rc = -errno;
                goto err;
        }

        DBG(SETUP, ul_debugobj(lc, "device open: OK"));

        /*
         * Atomic way to configure all by one ioctl call
         * -- since Linux v5.8-rc1, commit 3448914e8cc550ba792d4ccc74471d1ca4293aae
         */
        lc->config.fd = file_fd;
        if (lc->blocksize > 0)
                lc->config.block_size = lc->blocksize;

        rc = repeat_on_eagain( ioctl(dev_fd, LOOP_CONFIGURE, &lc->config) );
        if (rc != 0) {
                errsv = errno;
                if (errno != EINVAL && errno != ENOTTY && errno != ENOSYS) {
                        DBG(SETUP, ul_debugobj(lc, "LOOP_CONFIGURE failed: %m"));
                        goto err;
                }
                fallback = 1;
        } else {
                DBG(SETUP, ul_debugobj(lc, "LOOP_CONFIGURE: OK"));
        }

        /*
         * Old deprecated way; first assign backing file FD and then in the
         * second step set loop device properties.
         */
        if (fallback) {
                if (ioctl(dev_fd, LOOP_SET_FD, file_fd) < 0) {
                        rc = -errno;
                        errsv = errno;
                        DBG(SETUP, ul_debugobj(lc, "LOOP_SET_FD failed: %m"));
                        goto err;
                }

                DBG(SETUP, ul_debugobj(lc, "LOOP_SET_FD: OK"));

                if (lc->blocksize > 0
                        && (rc = loopcxt_ioctl_blocksize(lc, lc->blocksize)) < 0) {
                        errsv = -rc;
                        goto err;
                }

                if ((rc = loopcxt_ioctl_status(lc)) < 0) {
                        errsv = -rc;
                        goto err;
                }
        }

        if ((rc = loopcxt_check_size(lc, file_fd)))
                goto err;

        close(file_fd);

        memset(&lc->config, 0, sizeof(lc->config));
        lc->has_info = 0;
        lc->info_failed = 0;

        DBG(SETUP, ul_debugobj(lc, "success [rc=0]"));
        return 0;
err:
        if (file_fd >= 0)
                close(file_fd);
        if (dev_fd >= 0 && rc != -EBUSY)
                ioctl(dev_fd, LOOP_CLR_FD, 0);
        if (errsv)
                errno = errsv;

        DBG(SETUP, ul_debugobj(lc, "failed [rc=%d]", rc));
        return rc;
}


/*
 * @lc: context
 *
 * Update status of the current device (see loopcxt_{set,get}_device()).
 *
 * Note that once initialized, kernel accepts only selected changes:
 * LO_FLAGS_AUTOCLEAR and LO_FLAGS_PARTSCAN
 * For more see linux/drivers/block/loop.c:loop_set_status()
 *
 * Returns: <0 on error, 0 on success.
 */
int loopcxt_ioctl_status(struct loopdev_cxt *lc)
{
        int dev_fd, rc;

        errno = 0;
        dev_fd = loopcxt_get_fd(lc);

        if (dev_fd < 0)
                return -errno;

        DBG(SETUP, ul_debugobj(lc, "calling LOOP_SET_STATUS64"));

        rc = repeat_on_eagain( ioctl(dev_fd, LOOP_SET_STATUS64, &lc->config.info) );
        if (rc != 0) {
                DBG(SETUP, ul_debugobj(lc, "LOOP_SET_STATUS64 failed: %m"));
                return rc;
        }

        DBG(SETUP, ul_debugobj(lc, "LOOP_SET_STATUS64: OK"));
        return 0;
}

int loopcxt_ioctl_capacity(struct loopdev_cxt *lc)
{
        int rc, fd = loopcxt_get_fd(lc);

        if (fd < 0)
                return -EINVAL;

        DBG(SETUP, ul_debugobj(lc, "calling LOOP_SET_CAPACITY"));

        /* Kernels prior to v2.6.30 don't support this ioctl */
        rc = repeat_on_eagain( ioctl(fd, LOOP_SET_CAPACITY, 0) );
        if (rc != 0) {
                DBG(CXT, ul_debugobj(lc, "LOOP_SET_CAPACITY failed: %m"));
                return rc;
        }

        DBG(CXT, ul_debugobj(lc, "capacity set"));
        return 0;
}

int loopcxt_ioctl_dio(struct loopdev_cxt *lc, unsigned long use_dio)
{
        int rc, fd = loopcxt_get_fd(lc);

        if (fd < 0)
                return -EINVAL;

        DBG(SETUP, ul_debugobj(lc, "calling LOOP_SET_DIRECT_IO"));

        /* Kernels prior to v4.4 don't support this ioctl */
        rc = repeat_on_eagain( ioctl(fd, LOOP_SET_DIRECT_IO, use_dio) );
        if (rc != 0) {
                DBG(CXT, ul_debugobj(lc, "LOOP_SET_DIRECT_IO failed: %m"));
                return rc;
        }

        DBG(CXT, ul_debugobj(lc, "direct io set"));
        return 0;
}

/*
 * Kernel uses "unsigned long" as ioctl arg, but we use u64 for all sizes to
 * keep loopdev internal API simple.
 */
int loopcxt_ioctl_blocksize(struct loopdev_cxt *lc, uint64_t blocksize)
{
        int rc, fd = loopcxt_get_fd(lc);

        if (fd < 0)
                return -EINVAL;

        DBG(SETUP, ul_debugobj(lc, "calling LOOP_SET_BLOCK_SIZE"));

        rc = repeat_on_eagain(
                ioctl(fd, LOOP_SET_BLOCK_SIZE, (unsigned long) blocksize) );
        if (rc != 0) {
                DBG(CXT, ul_debugobj(lc, "LOOP_SET_BLOCK_SIZE failed: %m"));
                return rc;
        }

        DBG(CXT, ul_debugobj(lc, "logical block size set"));
        return 0;
}

int loopcxt_delete_device(struct loopdev_cxt *lc)
{
        int rc, fd = loopcxt_get_fd(lc);

        if (fd < 0)
                return -EINVAL;

        DBG(SETUP, ul_debugobj(lc, "calling LOOP_SET_CLR_FD"));

        rc = repeat_on_eagain( ioctl(fd, LOOP_CLR_FD, 0) );
        if (rc != 0) {
                DBG(CXT, ul_debugobj(lc, "LOOP_CLR_FD failed: %m"));
                return rc;
        }

        DBG(CXT, ul_debugobj(lc, "device removed"));
        return 0;
}

int loopcxt_add_device(struct loopdev_cxt *lc)
{
        int rc = -EINVAL;
        int ctl, nr = -1;
        const char *p, *dev = loopcxt_get_device(lc);

        if (!dev)
                goto done;

        if (!(lc->flags & LOOPDEV_FL_CONTROL)) {
                rc = -ENOSYS;
                goto done;
        }

        p = strrchr(dev, '/');
        if (!p || (sscanf(p, "/loop%d", &nr) != 1 && sscanf(p, "/%d", &nr) != 1)
               || nr < 0)
                goto done;

        ctl = open(_PATH_DEV_LOOPCTL, O_RDWR|O_CLOEXEC);
        if (ctl >= 0) {
                DBG(CXT, ul_debugobj(lc, "add_device %d", nr));
                rc = ioctl(ctl, LOOP_CTL_ADD, nr);
                close(ctl);
        }
        lc->control_ok = rc >= 0 ? 1 : 0;
done:
        DBG(CXT, ul_debugobj(lc, "add_device done [rc=%d]", rc));
        return rc;
}

/*
 * Note that LOOP_CTL_GET_FREE ioctl is supported since kernel 3.1. In older
 * kernels we have to check all loop devices to found unused one.
 *
 * See kernel commit 770fe30a46a12b6fb6b63fbe1737654d28e8484.
 *
 * Returns: 0 = success, < 0 error
 */
int loopcxt_find_unused(struct loopdev_cxt *lc)
{
        int rc = -1;

        DBG(CXT, ul_debugobj(lc, "find_unused requested"));

        if (lc->flags & LOOPDEV_FL_CONTROL) {
                int ctl;

                DBG(CXT, ul_debugobj(lc, "using loop-control"));

                ctl = open(_PATH_DEV_LOOPCTL, O_RDWR|O_CLOEXEC);
                if (ctl >= 0)
                        rc = ioctl(ctl, LOOP_CTL_GET_FREE);
                else
                        rc = -errno;
                if (rc >= 0) {
                        char name[16];
                        snprintf(name, sizeof(name), "loop%d", rc);

                        rc = loopiter_set_device(lc, name);
                }
                lc->control_ok = ctl >= 0 && rc == 0 ? 1 : 0;
                if (ctl >= 0)
                        close(ctl);
                DBG(CXT, ul_debugobj(lc, "find_unused by loop-control [rc=%d]", rc));
        }

        if (rc < 0) {
                DBG(CXT, ul_debugobj(lc, "using loop scan"));
                rc = loopcxt_init_iterator(lc, LOOPITER_FL_FREE);
                if (rc)
                        return rc;

                rc = loopcxt_next(lc);
                loopcxt_deinit_iterator(lc);
                DBG(CXT, ul_debugobj(lc, "find_unused by scan [rc=%d]", rc));
                if (rc)
                        return -ENOENT;
        }
        return rc;
}



/*
 * Return: TRUE/FALSE
 */
int loopdev_is_autoclear(const char *device)
{
        struct loopdev_cxt lc;
        int rc;

        if (!device)
                return 0;

        rc = loopcxt_init(&lc, 0);
        if (!rc)
                rc = loopcxt_set_device(&lc, device);
        if (!rc)
                rc = loopcxt_is_autoclear(&lc);

        loopcxt_deinit(&lc);
        return rc;
}

char *loopdev_get_backing_file(const char *device)
{
        struct loopdev_cxt lc;
        char *res = NULL;

        if (!device)
                return NULL;
        if (loopcxt_init(&lc, 0))
                return NULL;
        if (loopcxt_set_device(&lc, device) == 0)
                res = loopcxt_get_backing_file(&lc);

        loopcxt_deinit(&lc);
        return res;
}

/*
 * Returns: TRUE/FALSE
 */
int loopdev_has_backing_file(const char *device)
{
        char *tmp = loopdev_get_backing_file(device);

        if (tmp) {
                free(tmp);
                return 1;
        }
        return 0;
}

/*
 * Returns: TRUE/FALSE
 */
int loopdev_is_used(const char *device, const char *filename,
                    uint64_t offset, uint64_t sizelimit, int flags)
{
        struct loopdev_cxt lc;
        struct stat st;
        int rc = 0;

        if (!device || !filename)
                return 0;

        rc = loopcxt_init(&lc, 0);
        if (!rc)
                rc = loopcxt_set_device(&lc, device);
        if (rc)
                return rc;

        rc = !stat(filename, &st);
        rc = loopcxt_is_used(&lc, rc ? &st : NULL, filename, offset, sizelimit, flags);

        loopcxt_deinit(&lc);
        return rc;
}

/*
 * Returns: 0 = success, < 0 error
 */
int loopdev_delete(const char *device)
{
        struct loopdev_cxt lc;
        int rc;

        if (!device)
                return -EINVAL;

        rc = loopcxt_init(&lc, 0);
        if (!rc)
                rc = loopcxt_set_device(&lc, device);
        if (!rc)
                rc = loopcxt_delete_device(&lc);
        loopcxt_deinit(&lc);
        return rc;
}

/*
 * Returns: 0 = success, < 0 error, 1 not found
 */
int loopcxt_find_by_backing_file(struct loopdev_cxt *lc, const char *filename,
                                 uint64_t offset, uint64_t sizelimit, int flags)
{
        int rc, hasst;
        struct stat st;

        if (!filename)
                return -EINVAL;

        hasst = !stat(filename, &st);

        rc = loopcxt_init_iterator(lc, LOOPITER_FL_USED);
        if (rc)
                return rc;

        while ((rc = loopcxt_next(lc)) == 0) {

                if (loopcxt_is_used(lc, hasst ? &st : NULL,
                                    filename, offset, sizelimit, flags))
                        break;
        }

        loopcxt_deinit_iterator(lc);
        return rc;
}

/*
 * Returns: 0 = not found, < 0 error, 1 found, 2 found full size and offset match
 */
int loopcxt_find_overlap(struct loopdev_cxt *lc, const char *filename,
                           uint64_t offset, uint64_t sizelimit)
{
        int rc, hasst;
        struct stat st;

        if (!filename)
                return -EINVAL;

        DBG(CXT, ul_debugobj(lc, "find_overlap requested"));
        hasst = !stat(filename, &st);

        rc = loopcxt_init_iterator(lc, LOOPITER_FL_USED);
        if (rc)
                return rc;

        while ((rc = loopcxt_next(lc)) == 0) {
                uint64_t lc_sizelimit, lc_offset;

                rc = loopcxt_is_used(lc, hasst ? &st : NULL,
                                     filename, offset, sizelimit, 0);
                /*
                 * Either the loopdev is unused or we've got an error which can
                 * happen when we are racing with device autoclear. Just ignore
                 * this loopdev...
                 */
                if (rc <= 0)
                        continue;

                DBG(CXT, ul_debugobj(lc, "found %s backed by %s",
                        loopcxt_get_device(lc), filename));

                rc = loopcxt_get_offset(lc, &lc_offset);
                if (rc) {
                        DBG(CXT, ul_debugobj(lc, "failed to get offset for device %s",
                                loopcxt_get_device(lc)));
                        continue;
                }
                rc = loopcxt_get_sizelimit(lc, &lc_sizelimit);
                if (rc) {
                        DBG(CXT, ul_debugobj(lc, "failed to get sizelimit for device %s",
                                loopcxt_get_device(lc)));
                        continue;
                }

                /* full match */
                if (lc_sizelimit == sizelimit && lc_offset == offset) {
                        DBG(CXT, ul_debugobj(lc, "overlapping loop device %s (full match)",
                                                loopcxt_get_device(lc)));
                        rc = 2;
                        goto found;
                }

                /* overlap */
                if (lc_sizelimit != 0 && offset >= lc_offset + lc_sizelimit)
                        continue;
                if (sizelimit != 0 && offset + sizelimit <= lc_offset)
                        continue;

                DBG(CXT, ul_debugobj(lc, "overlapping loop device %s",
                        loopcxt_get_device(lc)));
                        rc = 1;
                        goto found;
        }

        if (rc == 1)
                rc = 0; /* not found */
found:
        loopcxt_deinit_iterator(lc);
        DBG(CXT, ul_debugobj(lc, "find_overlap done [rc=%d]", rc));
        return rc;
}

/*
 * Returns allocated string with device name
 */
char *loopdev_find_by_backing_file(const char *filename, uint64_t offset, uint64_t sizelimit, int flags)
{
        struct loopdev_cxt lc;
        char *res = NULL;

        if (!filename)
                return NULL;

        if (loopcxt_init(&lc, 0))
                return NULL;
        if (loopcxt_find_by_backing_file(&lc, filename, offset, sizelimit, flags) == 0)
                res = loopcxt_strdup_device(&lc);
        loopcxt_deinit(&lc);

        return res;
}

/*
 * Returns number of loop devices associated with @file, if only one loop
 * device is associated with the given @filename and @loopdev is not NULL then
 * @loopdev returns name of the device.
 */
int loopdev_count_by_backing_file(const char *filename, char **loopdev)
{
        struct loopdev_cxt lc;
        int count = 0, rc;

        if (!filename)
                return -1;

        rc = loopcxt_init(&lc, 0);
        if (rc)
                return rc;
        if (loopcxt_init_iterator(&lc, LOOPITER_FL_USED))
                return -1;

        while(loopcxt_next(&lc) == 0) {
                char *backing = loopcxt_get_backing_file(&lc);

                if (!backing || strcmp(backing, filename) != 0) {
                        free(backing);
                        continue;
                }

                free(backing);
                if (loopdev && count == 0)
                        *loopdev = loopcxt_strdup_device(&lc);
                count++;
        }

        loopcxt_deinit(&lc);

        if (loopdev && count > 1) {
                free(*loopdev);
                *loopdev = NULL;
        }
        return count;
}

#ifdef TEST_PROGRAM_LOOPDEV
int main(int argc, char *argv[])
{
        if (argc < 2)
                goto usage;

        if (strcmp(argv[1], "--is-loopdev") == 0 && argc == 3)
                printf("%s: %s\n", argv[2], is_loopdev(argv[2]) ? "OK" : "FAIL");
        else
                goto usage;

        return EXIT_SUCCESS;
usage:
        fprintf(stderr, "usage: %1$s --is-loopdev <dev>\n",
                        program_invocation_short_name);
        return EXIT_FAILURE;
}
#endif