udf: Use device size when drive reported bogus number of written blocks

Some drives report 0 as the number of written blocks when there are some blocks
recorded. Use device size in such case so that we can automagically mount such
media.

Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 6 insertions, 1 deletions

diff --git a/fs/udf/lowlevel.c b/fs/udf/lowlevel.c
index 703843f30ffd..1b88fd5df05d 100644
--- a/fs/udf/lowlevel.c
+++ b/fs/udf/lowlevel.c
@@ -56,7 +56,12 @@ unsigned long udf_get_last_block(struct super_block *sb)
         struct block_device *bdev = sb->s_bdev;
         unsigned long lblock = 0;
 
-        if (ioctl_by_bdev(bdev, CDROM_LAST_WRITTEN, (unsigned long) &lblock))
+        /*
+         * ioctl failed or returned obviously bogus value?
+         * Try using the device size...
+         */
+        if (ioctl_by_bdev(bdev, CDROM_LAST_WRITTEN, (unsigned long) &lblock) ||
+            lblock == 0)
                 lblock = bdev->bd_inode->i_size >> sb->s_blocksize_bits;
 
         if (lblock)