On 12/08/2017 08:02 PM, Qu Wenruo wrote:
On 2017年12月08日 19:48, Anand Jain wrote:
On 12/08/2017 07:01 PM, Qu Wenruo wrote:
On 2017年12月08日 18:39, Anand Jain wrote:
On 12/08/2017 04:17 PM, 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.
Theoretical design helps. I ended up in this situation though. And
ext4 has -o sb flag to manage this part. When we can expect EIO on
any part of the disk block why not on the LBA which contains primary
SB. And should we fail the mount for that reason ? No.
And how do you ensure it's a btrfs?
Hmm. You mean outside of btrfs ? I did experiment with wipe and then
using /etc/fstab to mount, and it did lead to btrfs, is that your
concern that it shouldn't have been. That looked surprising to me as
well, but then problem points at wipefs instead.
It's closer, but still doesn't reach the point.
It can be a mkfs, other than wipefs.
It's can be another case like:
One user used btrfs for a while
But bugs made him/her unhappy, and he/she turned to use xfs (whatever
the fs is) instead.
While he/she forgot to change its fstab, and rebooted the system.
And suddenly, it's btrfs again!
What a surprise.
I have worked quite a lot on defining the problem statements before
btrfs. Here the user has to be blamed to have forgotten to update
the fstab. I don't understand why should we workaround in btrfs for
the reason that user may miss to update fstab. We don't design
a stuff that like that, we design for the purpose, here backup SB
is for the purpose that we all know, if we don't use backup SB, then
its an incomplete design.
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.
Of course, we already have btrfs_check_super_valid() to verify the SB,
I don't understand why - how do we verify the SB should be the
point of
concern here, at all.
The point here is, to distinguish an old and invalid btrfs (some other
valid fs mkfs beyond the old fs) from a valid btrfs with corrupted
primary fs.
Ok. When you check all the SBs you would pick the one which has passed
btrfs_check_super_valid() and has highest generation. Did I ans your
concern ? If a SB does not pass btrfs_check_super_valid() its not a
valid btrfs SB at all.
No, not really.
What if the first SB is a XFS one or even a fs you didn't ever hear?
Skip it and use the 2nd one?
This filesystem is not even btrfs anymore.
There is no problem is user does the correct thing that is to
update the fstab. OR using a complete mount command. If user
using -t btrfs OR unupdated btrfs then it indicates his intentions.
Thanks, Anand
Thanks,
Qu
This the main concern here.
The difference between recovery and recognizing a bad btrfs is quite
important.
btrfs_check_super_valid() is already doing that right ? The point here
is, should we use the backup SB when btrfs_check_super_valid() fails on
primary SB.
Thanks, Anand
Thanks,
Qu
Thanks, Anand
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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