On Tue, Oct 13, 2015 at 07:40:30PM +0800, Zhao Lei wrote:
> > What I remember from the comment is that "it's slightly offset that would lead
> > to corruption".
>
> Before this patch, I had done git blame to search why the condition was added,
> and hadn't found the exact reason.
found it: commit bc3f116fec194f1d7329b160c266fe16b9266a1e and it was not
aobut data/dup but mixed bgs with sectorisze != nodesize:
26 + nodesize = btrfs_super_nodesize(disk_super);
27 + leafsize = btrfs_super_leafsize(disk_super);
28 + sectorsize = btrfs_super_sectorsize(disk_super);
29 + stripesize = btrfs_super_stripesize(disk_super);
30 +
31 + /*
32 + * mixed block groups end up with duplicate but slightly offset
33 + * extent buffers for the same range. It leads to corruptions
34 + */
35 + if ((features & BTRFS_FEATURE_INCOMPAT_MIXED_GROUPS) &&
36 + (sectorsize != leafsize)) {
37 + printk(KERN_WARNING "btrfs: unequal leaf/node/sector sizes "
38 + "are not allowed for mixed block groups on %s\n",
39 + sb->s_id);
40 + goto fail_alloc;
41 + }
42 +
> I will queue xfstests(btrfs/generic) at this profile with all mount option
> for multi-times, to check is something wrong with this.
Thanks. We need to cover more: the balance conversion forbids data/dup profile,
I'm not sure if scrub handles that properly, and the ususal suspects in the
rescue tools (fsck, restore, chunk-recover).
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