mount: improve --move error message on shared trees

Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/sys-utils/mount.8 b/sys-utils/mount.8
index f634b27fd926c98ca46f93cf1f87fa8e5538dc63..1702c4688d59d4a92c4e24fdf586cdfdcde10385 100644 (file)
--- a/sys-utils/mount.8
+++ b/sys-utils/mount.8
@@ -448,6 +448,11 @@ accessed under newdir.  The physical location of the files is not changed.
 Note that the
 .I olddir
 has to be a mountpoint.
+
+Note that moving a mount residing under a shared mount is invalid and
+unsupported. Use
+.B findmnt -o TARGET,PROPAGATION /dir
+to see the current propagation flags.
 .RE
 
 .B The shared subtrees operations.

diff --git a/sys-utils/mount.c b/sys-utils/mount.c
index ebdfe885d66660d0df2b029573dd2edee72a5b0c..664c46f6b459cdad9ec25f7fc87960d54578479f 100644 (file)
--- a/sys-utils/mount.c
+++ b/sys-utils/mount.c
@@ -321,6 +321,37 @@ static void selinux_warning(struct libmnt_context *cxt, const char *tgt)
 # define selinux_warning(_x, _y)
 #endif
 
+/*
+ * Returns 1 if @dir parent is shared
+ */
+static int is_shared_tree(struct libmnt_context *cxt, const char *dir)
+{
+       struct libmnt_table *tb = NULL;
+       struct libmnt_fs *fs;
+       unsigned long mflags = 0;
+       char *mnt = NULL, *p;
+       int rc = 0;
+
+       if (!dir)
+               return 0;
+       if (mnt_context_get_mtab(cxt, &tb) || !tb)
+               goto done;
+       mnt = xstrdup(dir);
+       p = strrchr(mnt, '/');
+       if (!p)
+               goto done;
+       if (p > mnt)
+               *p = '\0';
+       fs = mnt_table_find_mountpoint(tb, mnt, MNT_ITER_BACKWARD);
+
+       rc = fs && mnt_fs_is_kernel(fs)
+               && mnt_fs_get_propagation(fs, &mflags) == 0
+               && (mflags & MS_SHARED);
+done:
+       free(mnt);
+       return rc;
+}
+
 /*
  * rc = 0 success
  *     <0 error (usually -errno or -1)
@@ -475,11 +506,11 @@ try_readonly:
                break;
        }
        case ENOENT:
-               if (lstat(tgt, &st))
+               if (tgt && lstat(tgt, &st))
                        warnx(_("mount point %s does not exist"), tgt);
-               else if (stat(tgt, &st))
+               else if (tgt && stat(tgt, &st))
                        warnx(_("mount point %s is a symbolic link to nowhere"), tgt);
-               else if (stat(src, &st)) {
+               else if (src && stat(src, &st)) {
                        if (uflags & MNT_MS_NOFAIL)
                                return MOUNT_EX_SUCCESS;
 
@@ -493,7 +524,7 @@ try_readonly:
        case ENOTDIR:
                if (stat(tgt, &st) || ! S_ISDIR(st.st_mode))
                        warnx(_("mount point %s is not a directory"), tgt);
-               else if (stat(src, &st) && errno == ENOTDIR) {
+               else if (src && stat(src, &st) && errno == ENOTDIR) {
                        if (uflags & MNT_MS_NOFAIL)
                                return MOUNT_EX_SUCCESS;
 
@@ -510,6 +541,9 @@ try_readonly:
                        warnx(_("%s not mounted or bad option"), tgt);
                else if (rc == -MNT_ERR_APPLYFLAGS)
                        warnx(_("%s is not mountpoint or bad option"), tgt);
+               else if ((mflags & MS_MOVE) && is_shared_tree(cxt, src))
+                       warnx(_("bad option. Note that moving a mount residing under a shared\n"
+                               "       mount is unsupported."));
                else
                        warnx(_("wrong fs type, bad option, bad superblock on %s,\n"
                                "       missing codepage or helper program, or other error"),
@@ -520,9 +554,9 @@ try_readonly:
                                "       (for several filesystems (e.g. nfs, cifs) you might\n"
                                "       need a /sbin/mount.<type> helper program)\n"));
 
-               fprintf(stderr, _(
+               fprintf(stderr, _("\n"
                                "       In some cases useful info is found in syslog - try\n"
-                               "       dmesg | tail or so\n"));
+                               "       dmesg | tail or so.\n"));
                break;
 
        case EMFILE: