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.
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.j...@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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