libext2fs: check open(O_EXCL) first in ismounted.c

Currently the ext2fs_check_mount_point() will use the open(O_EXCL) check
on linux after all the other checks are done. However it is not
necessary to check mntent if open(O_EXCL) succeeds because it means that
the device is not mounted.

Moreover the commit ea4d53b7 introduced a regression where a following
set of commands fails:

vgcreate mygroup /dev/sda
lvcreate -L 1G -n lvol0 mygroup
mkfs.ext4 /dev/mygroup/lvol0
mount /dev/mygroup/lvol0 /mnt
lvrename /dev/mygroup/lvol0 /dev/mygroup/lvol1
lvcreate -L 1G -n lvol0 mygroup
mkfs.ext4 /dev/mygroup/lvol0   <<<--- This fails

It fails because it thinks that /dev/mygroup/lvol0 is mounted because
the device name in /proc/mounts is not updated following the lvrename.

Move the open(O_EXCL) check before the mntent check and return
immediatelly if the device is not busy.

Fixes: ea4d53b7 ("libext2fs/ismounted.c: check device id in advance to skip false device names")
Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Reported-by: Zdenek Kabelac <zkabelac@redhat.com>
Reported-by: Karel Zak <kzak@redhat.com>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/lib/ext2fs/ismounted.c b/lib/ext2fs/ismounted.c
index c02156925a8081831fca6348a4e620dadee003d8..46d330d986b228b4da45f5cfdd0eb09cc3bb81b5 100644 (file)
--- a/lib/ext2fs/ismounted.c
+++ b/lib/ext2fs/ismounted.c
@@ -352,6 +352,7 @@ errcode_t ext2fs_check_mount_point(const char *device, int *mount_flags,
                                  char *mtpt, int mtlen)
 {
        errcode_t       retval = 0;
+       int             busy = 0;
 
        if (getenv("EXT2FS_PRETEND_RO_MOUNT")) {
                *mount_flags = EXT2_MF_MOUNTED | EXT2_MF_READONLY;
@@ -366,6 +367,30 @@ errcode_t ext2fs_check_mount_point(const char *device, int *mount_flags,
                return 0;
        }
 
+#ifdef __linux__ /* This only works on Linux 2.6+ systems */
+       {
+               struct stat st_buf;
+
+               if (stat(device, &st_buf) == 0 &&
+                   ext2fsP_is_disk_device(st_buf.st_mode)) {
+                       int fd = open(device, O_RDONLY | O_EXCL);
+
+                       if (fd >= 0) {
+                               /*
+                                * The device is not busy so it's
+                                * definitelly not mounted. No need to
+                                * to perform any more checks.
+                                */
+                               close(fd);
+                               *mount_flags = 0;
+                               return 0;
+                       } else if (errno == EBUSY) {
+                               busy = 1;
+                       }
+               }
+       }
+#endif
+
        if (is_swap_device(device)) {
                *mount_flags = EXT2_MF_MOUNTED | EXT2_MF_SWAP;
                strncpy(mtpt, "<swap>", mtlen);
@@ -386,21 +411,8 @@ errcode_t ext2fs_check_mount_point(const char *device, int *mount_flags,
        if (retval)
                return retval;
 
-#ifdef __linux__ /* This only works on Linux 2.6+ systems */
-       {
-               struct stat st_buf;
-
-               if (stat(device, &st_buf) == 0 &&
-                   ext2fsP_is_disk_device(st_buf.st_mode)) {
-                       int fd = open(device, O_RDONLY | O_EXCL);
-
-                       if (fd >= 0)
-                               close(fd);
-                       else if (errno == EBUSY)
-                               *mount_flags |= EXT2_MF_BUSY;
-               }
-       }
-#endif
+       if (busy)
+               *mount_flags |= EXT2_MF_BUSY;
 
        return 0;
 }