Btrfs: Don't error on resizing FS to same size

It seems overly harsh to fail a resize of a btrfs file system to the same size when a shrink or grow would succeed. User app GParted trips over this error. Allow it by bypassing the shrink or grow operation.

---

v2: Fix FS shrink prevention error spotted by Chris Samuel

Example failed resize:

    # strace -e trace=ioctl btrfs filesystem resize max /mnt/0
    Resize '/mnt/0' of 'max'
    ioctl(3, 0x50009403, 0xbfa5029c)        = -1 EINVAL (Invalid argument)
    ERROR: unable to resize '/mnt/0' - Invalid argument
    # echo $?
    30
    # dmesg | tail -1
    [426094.235018] new size for /dev/loop1 is 1073741824

---
 fs/btrfs/ioctl.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

index dae5dfe..bd32cce 100644
@@ -1251,7 +1251,7 @@ static noinline int btrfs_ioctl_resize(struct btrfs_root *root,
 		}
 		ret = btrfs_grow_device(trans, device, new_size);
 		btrfs_commit_transaction(trans, root);
-	} else {
+	} else if (new_size < old_size) {
 		ret = btrfs_shrink_device(device, new_size);
 	}
 

1.7.4.4