linux-kernel - Re: [PATCH] nvmet-tcp: switch to using the crc32c library

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Message-ID: <7ccc3a88-b92c-45b8-bbfd-af98ab439be7@suse.de>
Date: Thu, 27 Feb 2025 08:26:05 +0100
From: Hannes Reinecke <hare@...e.de>
To: Eric Biggers <ebiggers@...nel.org>
Cc: Christoph Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>,
 Chaitanya Kulkarni <kch@...dia.com>, linux-nvme@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nvmet-tcp: switch to using the crc32c library

On 2/26/25 20:01, Eric Biggers wrote:
> On Wed, Feb 26, 2025 at 10:37:55AM +0100, Hannes Reinecke wrote:
>> ... and it also eliminates a sporadic crash which we've seen
>> where 'snd_hash' wasn't initialized when sending PDUs.
>> Thanks for doing this!
> 
> I'm not sure how that could have happened, since the ahash was allocated when
> 'if (queue->hdr_digest || queue->data_digest)' which seemed to match the
> conditions for when it was used.  But yeah, it's certainly nice to not have the
> pointless allocation to worry about.
> 
>> (Note to self: check the nvme-tls code for crc32c usage ...)
> 
> I have patches for nvme-tls almost ready too.  Just been taking my time since
> I've been updating all other users of "crc32" and "crc32c" in the kernel too.
> And I need to decide what to do about skb_copy_and_hash_datagram_iter().
> 
If it were me I would _love_ to switch the nvme-tcp recv patch over to 
recvmsg and kill the ->read_sock() implementation.
->read_sock uses a completely different codepath in tls_sw, and nvme is
the only user of that. So there's a fair chance that we might miss any
improvements or fixes.

Plus we currently have no good way of handling TLS records from 
->read_sock(), which is something we might want to do in the future.

So if we had an equivalent for skb_copy_and_hash_iter() for recvmsg()
I could revisit my original patchset and work on getting ->read_sock()
replaced.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@...e.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich