Re: [PATCH 3/4] btrfs: include non-missing as a qualifier for the latest_bdev

[Nikolay Borisov <nborisov@suse.com>]

On 4.10.19 г. 10:50 ч., Anand Jain wrote:
> btrfs_free_extra_devids() reorgs fs_devices::latest_bdev
> to point to the bdev with greatest device::generation number.
> For a typical-missing device the generation number is zero so
> fs_devices::latest_bdev will never point to it.
> 
> But if the missing device is due to alienating [1], then
> device::generation is not-zero and if it is >= to rest of
> device::generation in the list, then fs_devices::latest_bdev
> ends up pointing to the missing device and reports the error
> like this [2]
> 
> [1]
> mkfs.btrfs -fq /dev/sdd && mount /dev/sdd /btrfs
> mkfs.btrfs -fq -draid1 -mraid1 /dev/sdb /dev/sdc
> sleep 3 # avoid racing with udev's useless scans if needed
> btrfs dev add -f /dev/sdb /btrfs

Hm, here I think the correct way is to refuse adding /dev/sdb to an
existing fs if it's detected to be part of a different one. I.e it
should require wipefs to be done.

> 
> mount -o degraded /dev/sdc /btrfs1
> 
> [2]
> mount: wrong fs type, bad option, bad superblock on /dev/sdc,
>        missing codepage or helper program, or other error
> 
>        In some cases useful info is found in syslog - try
>        dmesg | tail or so.
> 
> kernel: BTRFS warning (device sdc): devid 1 uuid 072a0192-675b-4d5a-8640-a5cf2b2c704d is missing
> kernel: BTRFS error (device sdc): failed to read devices
> kernel: BTRFS error (device sdc): open_ctree failed
> 
> Fix the root of the issue, by checking if the the device is not
> missing before it can be a contender for the fs_devices::latest_bdev
> title.
> 
> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> ---
>  fs/btrfs/volumes.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 05ade8c7342b..6c42048ec099 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -1186,6 +1186,8 @@ void btrfs_free_extra_devids(struct btrfs_fs_devices *fs_devices, int step)
>  							&device->dev_state)) {
>  			if (!test_bit(BTRFS_DEV_STATE_REPLACE_TGT,
>  			     &device->dev_state) &&
> +			    !test_bit(BTRFS_DEV_STATE_MISSING,
> +			     &device->dev_state) &&
>  			     (!latest_dev ||
>  			      device->generation > latest_dev->generation)) {
>  				latest_dev = device;
>