On Thu, May 14, 2026 at 12:57:53PM -0700, H. Peter Anvin wrote:
On May 14, 2026 12:51:59 PM PDT, Goffredo Baroncelli [off-list ref] wrote:
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On 13/05/2026 07.47, Christoph Hellwig wrote:
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On Tue, May 12, 2026 at 01:42:31PM +0200, David Sterba wrote:
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The degenerate modes of
raid0, 5, or 6 are explicit as a possible middle step when converting
profiles. We can use a fallback implementation for this case if the
accelerated implementations cannot do it.
This is not about a degenerated mode. For a degenerated RAID 6, parity
generation uses the RAID 5 XOR routines as the second parity will be
missing. This is about generating two parities for a single data disk,
which must be explicitly selected.
I think that the David concern is : "what happens for an already
existing btrfs raid6 3 disks filesystem when the user upgrade the kernel ?"
(I am thinking when a new BG needs to be allocated)...
That's what I'm saying – it should invoke the RAID-1 code under the cover (as with 3 disks, D = P = Q.)
Thanks, it was not clear to me what you meant. For the two edge cases
the code should do simple memcpy for both calculations of parity and
recovery.