Re: [PATCH 0/5] Btrfs: Per-chunk degradable check

[Qu Wenruo <quwenruo@cn.fujitsu.com>]

Any new comment?

And to Chris, is it possible to pick these patchset for 4.4?

IMHO it's small enough (less than 100 lines) and didn't change degraded 
mount behavior much.

Thanks,
Qu

Qu Wenruo wrote on 2015/09/21 10:10 +0800:
> Btrfs currently uses num_tolerated_disk_barrier_failures to do global
> check for tolerated missing device.
>
> Although the one-size-fit-all solution is quite safe, it's too strict if
> data and metadata has different duplication level.
>
> For example, if one use Single data and RAID1 metadata for 2 disks, it
> means any missing device will make the fs unable to be degraded mounted.
>
> But in fact, some times all single chunks may be in the existing device
> and in that case, we should allow it to be rw degraded mounted.
>
> Such case can be easily reproduced using the following script:
>   # mkfs.btrfs -f -m raid1 -d sing /dev/sdb /dev/sdc
>   # wipefs -f /dev/sdc
>   # mount /dev/sdb -o degraded,rw
>
> If using btrfs-debug-tree to check /dev/sdb, one should find that the
> data chunk is only in sdb, so in fact it should allow degraded mount.
>
> This patchset will introduce a new per-chunk degradable check for btrfs,
> allow above case to succeed, and it's quite small anyway.
>
> Also, it provides the possibility for later enhancement, like
> automatically add 'degraded' mount option if possible.
>
> Cc: Anand Jain <anand.jain@oracle.com>
>
> Qu Wenruo (5):
>    btrfs: Introduce a new function to check if all chunks a OK for
>      degraded     mount
>    btrfs: Do per-chunk check for mount time check
>    btrfs: Do per-chunk degraded check for remount
>    btrfs: Allow barrier_all_devices to do per-chunk device check
>    btrfs: Cleanup num_tolerated_disk_barrier_failures
>
>   fs/btrfs/ctree.h   |  2 --
>   fs/btrfs/disk-io.c | 87 ++++++++++--------------------------------------------
>   fs/btrfs/disk-io.h |  2 --
>   fs/btrfs/super.c   | 11 ++++---
>   fs/btrfs/volumes.c | 84 +++++++++++++++++++++++++++++++++++++++++-----------
>   fs/btrfs/volumes.h |  5 ++++
>   6 files changed, 94 insertions(+), 97 deletions(-)
>