[PATCH] btrfs-progs: raid56: fix the wrong recovery condition for data and P case

[Qu Wenruo <wqu@suse.com>]

There is a bug in raid56_recov() which doesn't properly repair data and
P case corruption:

	/* Data and P*/
	if (dest2 == nr_devs - 1)
		return raid6_recov_datap(nr_devs, stripe_len, dest1, data);

Note that, dest1/2 is to indicate which slot has corruption.

For RAID6 cases:

[0, nr_devs - 2) is for data stripes,
@data_devs - 2 is for P,
@data_devs - 1 is for Q.

For above code, the comment is correct, but the check condition is
wrong, and leads to the only project, btrfs-fuse, to report raid6
recovery error for 2 devices missing case.

Fix it by using correct condition.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
But I'm more interested in why this function is still there, as there
seems to be no caller of this function in btrfs-progs anyway.
---
 kernel-lib/raid56.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel-lib/raid56.c b/kernel-lib/raid56.c
index a94a60ed73d0..6f690484c810 100644
--- a/kernel-lib/raid56.c
+++ b/kernel-lib/raid56.c
@@ -343,7 +343,7 @@ int raid56_recov(int nr_devs, size_t stripe_len, u64 profile, int dest1,
 		return raid6_recov_data2(nr_devs, stripe_len, dest1, dest2,
 					 data);
 	/* Data and P*/
-	if (dest2 == nr_devs - 1)
+	if (dest2 == nr_devs - 2)
 		return raid6_recov_datap(nr_devs, stripe_len, dest1, data);
 
 	/*
-- 
2.33.1