Re: [PATCH] Btrfs: check items for correctness as we search V3

[Chris Mason <chris.mason@oracle.com>]

Excerpts from Andrey Kuzmin's message of 2011-03-17 15:12:32 -0400:
> On Thu, Mar 17, 2011 at 9:18 PM, Josef Bacik <josef@redhat.com> wrote=
:
> > Currently if we have corrupted items things will blow up in spectac=
ular ways.
> > So as we read in blocks and they are leaves, check the entire leaf =
to make sure
> > all of the items are correct and point to valid parts in the leaf f=
or the item
> > data the are responsible for. =C2=A0If the item is corrupt we will =
kick back EIO and
> > not read any of the copies since they are likely to not be correct =
either. =C2=A0This
> > will catch generic corruptions, it will be up to the individual cal=
lers of
> > btrfs_search_slot to make sure their items are right. =C2=A0Thanks,
> >
> > diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> > index 495b1ac..9f31e11 100644
> > --- a/fs/btrfs/disk-io.c
> > +++ b/fs/btrfs/disk-io.c
> > @@ -323,6 +323,7 @@ static int btree_read_extent_buffer_pages(struc=
t btrfs_root *root,
> > =C2=A0 =C2=A0 =C2=A0 =C2=A0int num_copies =3D 0;
> > =C2=A0 =C2=A0 =C2=A0 =C2=A0int mirror_num =3D 0;
> >
> > + =C2=A0 =C2=A0 =C2=A0 clear_bit(EXTENT_BUFFER_CORRUPT, &eb->bflags=
);
> > =C2=A0 =C2=A0 =C2=A0 =C2=A0io_tree =3D &BTRFS_I(root->fs_info->btre=
e_inode)->io_tree;
> > =C2=A0 =C2=A0 =C2=A0 =C2=A0while (1) {
> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0ret =3D read=
_extent_buffer_pages(io_tree, eb, start, 1,
> > @@ -331,6 +332,14 @@ static int btree_read_extent_buffer_pages(stru=
ct btrfs_root *root,
> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0=
!verify_parent_transid(io_tree, eb, parent_transid))
> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0=
 =C2=A0 =C2=A0return ret;
> >
> > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 /*
> > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0* This buf=
fer's crc is fine, but its contents are corrupted, so
> > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0* there is=
 no reason to read the other copies, they won't be
> > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0* any less=
 wrong.
> > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0*/
>=20
> This sounds like an overstatement to me. You may be dealing with an
> error pattern CRC faled to catch, so giving up reading a mirror at
> this point seems premature.

But we have no way to tell which one is more correct, at least not
without a full fsck.

-chris
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