Re: [PATCH RFC] btrfs: self heal from SB fail

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

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On 2017年12月08日 20:51, Austin S. Hemmelgarn wrote:
> On 2017-12-08 02:57, Anand Jain wrote:
>> -EXPERIMENTAL-
>> As of now when primary SB fails we won't self heal and would fail mount,
>> this is an experimental patch which thinks why not go and read backup
>> copy.
> I like the concept, and actually think this should be default behavior
> on a filesystem that's already mounted (we fix other errors, why not
> SB's), but I don't think it should be default behavior at mount time for
> the reasons Qu has outlined (picking up old BTRFS SB's after
> reformatting is bad).  However, I do think it's useful to be able to ask
> for this behavior on mount, so that you don't need to fight with the
> programs to get a filesystem to mount when the first SB is missing
> (perhaps add a 'usebackupsb' option to mirror 'usebackuproot'?).

Yeah, I also like the idea of 'usebackupsuper'/'usebackupsuper=n' mount
option than do it automatically.

Thanks,
Qu

>>
>> Signed-off-by: Anand Jain <anand.jain@oracle.com>
>> ---
>>   fs/btrfs/disk-io.c |  8 +++++++-
>>   fs/btrfs/volumes.c | 10 +++++++---
>>   2 files changed, 14 insertions(+), 4 deletions(-)
>>
>> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
>> index 9b20c1f3563b..a791b8dfe8a8 100644
>> --- a/fs/btrfs/disk-io.c
>> +++ b/fs/btrfs/disk-io.c
>> @@ -3190,7 +3190,7 @@ struct buffer_head *btrfs_read_dev_super(struct
>> block_device *bdev)
>>        * So, we need to add a special mount option to scan for
>>        * later supers, using BTRFS_SUPER_MIRROR_MAX instead
>>        */
>> -    for (i = 0; i < 1; i++) {
>> +    for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
>>           ret = btrfs_read_dev_one_super(bdev, i, &bh);
>>           if (ret)
>>               continue;
>> @@ -4015,11 +4015,17 @@ static int btrfs_check_super_valid(struct
>> btrfs_fs_info *fs_info)
>>           ret = -EINVAL;
>>       }
>>   +#if 0
>> +    /*
>> +     * Need a way to check for any copy of SB, as its not a
>> +     * strong check, just ignore this for now.
>> +     */
>>       if (btrfs_super_bytenr(sb) != BTRFS_SUPER_INFO_OFFSET) {
>>           btrfs_err(fs_info, "super offset mismatch %llu != %u",
>>                 btrfs_super_bytenr(sb), BTRFS_SUPER_INFO_OFFSET);
>>           ret = -EINVAL;
>>       }
>> +#endif
>>         /*
>>        * Obvious sys_chunk_array corruptions, it must hold at least
>> one key
>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
>> index 9fa2539a8493..f368db94d62b 100644
>> --- a/fs/btrfs/volumes.c
>> +++ b/fs/btrfs/volumes.c
>> @@ -1369,7 +1369,7 @@ int btrfs_scan_one_device(const char *path,
>> fmode_t flags, void *holder,
>>   {
>>       struct btrfs_super_block *disk_super;
>>       struct block_device *bdev;
>> -    struct page *page;
>> +    struct buffer_head *sb_bh;
>>       int ret = -EINVAL;
>>       u64 devid;
>>       u64 transid;
>> @@ -1392,8 +1392,12 @@ int btrfs_scan_one_device(const char *path,
>> fmode_t flags, void *holder,
>>           goto error;
>>       }
>>   -    if (btrfs_read_disk_super(bdev, bytenr, &page, &disk_super))
>> +    sb_bh = btrfs_read_dev_super(bdev);
>> +    if (IS_ERR(sb_bh)) {
>> +        ret = PTR_ERR(sb_bh);
>>           goto error_bdev_put;
>> +    }
>> +    disk_super = (struct btrfs_super_block *) sb_bh->b_data;
>>         devid = btrfs_stack_device_id(&disk_super->dev_item);
>>       transid = btrfs_super_generation(disk_super);
>> @@ -1413,7 +1417,7 @@ int btrfs_scan_one_device(const char *path,
>> fmode_t flags, void *holder,
>>       if (!ret && fs_devices_ret)
>>           (*fs_devices_ret)->total_devices = total_devices;
>>   -    btrfs_release_disk_super(page);
>> +    brelse(sb_bh);
>>     error_bdev_put:
>>       blkdev_put(bdev, flags);
>>
> 
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