Hi I was looking at qgroups in linux 4.2 and noticed that the code to handle subvolume deletion was removed and replaced with a comment:
/* * TODO: Modify related function to add related node/leaf to * dirty_extent_root, * for later qgroup accounting. * * Current, this function does nothing. */ The commit in question is 0ed4792af0e8346cb670b4bc540df7594f4b2020, "btrfs: qgroup: Switch to new extent-oriented qgroup mechanism." Sure enough, I can reproduce an inconsistency by just removing a subvolume with more than 1 level. A script to reproduce this is attached to my e-mail (it's from the last time I fixed subvolume delete). This does not happen with Kernel 4.1. I also found the following in an e-mail from Qu a few weeks ago on the list: "And we still don't have a good idea to fix the snapshot deletion bug. (My patchset can only handle snapshot with up to 2 levels. With higher level, the qgroup number will still be wrong until related node/leaves are all COWed)" http://www.spinics.net/lists/linux-btrfs/msg45724.html So did we just commit another qgroup rewrite while knowingly re-introducing a major regression without a plan to fix it, or am I crazy? If there *is* a plan to make this all work again, can I please hear it? The comment mentions something about adding those nodes to a dirty_extent_root. Why wasn't that done? Thanks, --Mark #! /bin/bash SCRATCH_MNT="/btrfs" SCRATCH_DEV=/dev/vdb1 BTRFS_UTIL_PROG=btrfs echo "format, mount fs" mkfs.btrfs -f $SCRATCH_DEV mount -t btrfs $SCRATCH_DEV $SCRATCH_MNT # This always reproduces level 1 trees maxfiles=100 echo "create file set" # Make a bunch of small files in a directory. This is designed to expand # the filesystem tree to something more than zero levels. mkdir $SCRATCH_MNT/files for i in `seq -w 0 $maxfiles`; do dd status=none if=/dev/zero of=$SCRATCH_MNT/files/file$i bs=4096 count=4 done # create a snapshot of what we just did $BTRFS_UTIL_PROG fi sy $SCRATCH_MNT $BTRFS_UTIL_PROG su sna $SCRATCH_MNT $SCRATCH_MNT/snap1 mv $SCRATCH_MNT/snap1/files $SCRATCH_MNT/snap1/old # same thing as before but on the snapshot. this way we can generate # some exclusively owned tree nodes. echo "create file set on snapshot" mkdir $SCRATCH_MNT/snap1/files for i in `seq -w 0 $maxfiles`; do dd status=none if=/dev/zero of=$SCRATCH_MNT/snap1/files/file$i bs=4096 count=4 done SECS=30 echo "sleep for $SECS seconds" # Enable qgroups now that we have our filesystem prepared. This # will kick off a scan which we will have to wait for below. $BTRFS_UTIL_PROG qu en $SCRATCH_MNT sleep $SECS echo "unmount, remount fs to clear cache" umount $SCRATCH_MNT mount -t btrfs $SCRATCH_DEV $SCRATCH_MNT SECS=45 echo "delete snapshot, sleep for $SECS seconds" # Ok, delete the snapshot we made previously. Since btrfs drop # snapshot is a delayed action with no way to force it, we have to # impose another sleep here. $BTRFS_UTIL_PROG su de $SCRATCH_MNT/snap1 sleep $SECS echo "unmount" umount $SCRATCH_MNT # generate a qgroup report and look for inconsistent groups $BTRFS_UTIL_PROG check --qgroup-report $SCRATCH_DEV exit -- 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
