On 12/08/2017 09:17 AM, Qu Wenruo wrote:
>
>
> On 2017年12月08日 15:57, 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.
>
> Just curious about in which real world case that backup super block can
> help.
> At least from what I see in mail list, only few cases where backup super
> helps.
That's about using 'backup roots' with old info about previous
generations than the current one on disk, which is a different thing
than using one of the other copies of the super block itself.
> Despite that self super heal seems good, although I agree with David, we
> need a weaker but necessary check (magic and fsid from primary super?)
> to ensure it's a valid btrfs before we use the backup supers.
>
> Thanks,
> Qu
>
>
>>
>> Signed-off-by: Anand Jain <anand.jain@xxxxxxxxxx>
>> ---
>> 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);
>>
>
--
Hans van Kranenburg
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