Hi, while still busy with btrfs send, I came across some strange DIR_ITEMs. I looked into that briefly, but I'd rather return to implementing btrfs send, hoping someone is willing to make up his mind on this one :-)
To reproduce, do the following: # mkfs.btrfs /dev/sdv2 # mount /dev/sdv2 /mnt # btrfs subvol snap /mnt /mnt/snap1 You've a freshly created snapshot. However, file tree 256 (the snap1-tree) will contain two strange items: item 2 key (256 DIR_ITEM 3645318598) itemoff 3788 itemsize 35 location key (256 ROOT_ITEM 18446744073709551615) type 2 namelen 5 datalen 0 name: snap1 item 3 key (256 DIR_INDEX 2) itemoff 3753 itemsize 35 location key (256 ROOT_ITEM 18446744073709551615) type 2 namelen 5 datalen 0 name: snap1 These items are needed in tree 5 (fs tree) to reference snap1. However, within snap1, I'd not expect the entries. A brief look into create_pending_snapshot reveals ... btrfs_insert_dir_item() ... /* some delayed stuff with scary comments */ ... btrfs_cow_block() ... I'm not sure whether cowing earlier would help, I'm particularly uncertain because of the run_delayed_* code in between. So I haven't tried to fix this, I'm convinced it should be fixed, though. These items lead to some strange effects: # cd /mnt/snap1 # ls -l dr-xr-xr-x 1 root root 10 Jan 1 1970 . dr-xr-xr-x 1 root root 16 Oct 18 15:56 .. # mkdir snap1 mkdir: cannot create directory `snap1': File exists # stat snap1 File: `snap1' Size: 0 Blocks: 0 IO Block: 4096 directory Device: 11h/17d Inode: 2 Links: 1 # rmdir snap1 # stat snap1 stat: cannot stat `snap1': No such file or directory Inode number 2 seems to be BTRFS_EMPTY_SUBVOL_DIR_OBJECTID, the pseudo object is created by btrfs_lookup_dentry() in inode.c when ENOENT is encountered. As a side note: the timestamp of the snap-dir item could be prettier. No such pseudo items are created when the snapshot is placed outside of the subvolume to be snapshotted, obviously. In the above example, do ... # btrfs subvol snap /mnt/snap1 /mnt/snap2 ... and no such items will be created, which makes me quite certain the existence of above mentioned DIR_ITEMs is a bug, isn't it? -Jan -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html