On 2017年12月08日 22:02, Anand Jain wrote: > > > On 12/08/2017 08:51 PM, 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). > > If the primary SB is not btrfs, then unless forced with -t btrfs > option, this mount won't be in btrfs at all. That means it goes to > the respective FS by default. > > If the old btrfs is over written with newer btrfs SB, and if mkfs.btrfs > is not overwriting all the copies of SB then its a mkfs.btrfs bug.
Nope.
If the new btrfs is a smaller one than original btrfs, the 2nd super can
still be there.
(AFAIK all these examples have been given by David for several times)
Thanks,
Qu
>
> Which means there is already mount -t option to redirect to the FS
> module that is needed by the user, when primary SB is corrupted.
> We should use this feature.
>
> Thanks, Anand
>
>
>> 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'?).
>>>
>>> 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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