linux-kernel - Re: [PATCH v5 02/12] crypto: acomp - Define new interfaces for compress/decompress batching.

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Message-ID: <Z7qYUCAqh2YFQ908@gondor.apana.org.au>
Date: Sun, 23 Feb 2025 11:38:56 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Sergey Senozhatsky <senozhatsky@...omium.org>
Cc: Barry Song <21cnbao@...il.com>, Yosry Ahmed <yosry.ahmed@...ux.dev>,
	Minchan Kim <minchan@...nel.org>,
	"Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	"nphamcs@...il.com" <nphamcs@...il.com>,
	"chengming.zhou@...ux.dev" <chengming.zhou@...ux.dev>,
	"usamaarif642@...il.com" <usamaarif642@...il.com>,
	"ryan.roberts@....com" <ryan.roberts@....com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"clabbe@...libre.com" <clabbe@...libre.com>,
	"ardb@...nel.org" <ardb@...nel.org>,
	"ebiggers@...gle.com" <ebiggers@...gle.com>,
	"surenb@...gle.com" <surenb@...gle.com>,
	"Accardi, Kristen C" <kristen.c.accardi@...el.com>,
	"Feghali, Wajdi K" <wajdi.k.feghali@...el.com>,
	"Gopal, Vinodh" <vinodh.gopal@...el.com>
Subject: Re: [PATCH v5 02/12] crypto: acomp - Define new interfaces for
 compress/decompress batching.

On Sun, Feb 23, 2025 at 12:12:47PM +0900, Sergey Senozhatsky wrote:
>
> > > It also seems that there is no common way of reporting dst_but overflow.
> > > Some algos return -ENOSPC immediately, some don't return anything at all,
> > > and deflate does it's own thing - there are these places where they see
> > > they are out of out space but they Z_OK it
> > > 
> > > if (s->pending != 0) {
> > > 	flush_pending(strm);
> > > 	if (strm->avail_out == 0) {
> > > 		/* Since avail_out is 0, deflate will be called again with
> > > 		 * more output space, but possibly with both pending and
> > > 		 * avail_in equal to zero. There won't be anything to do,
> > > 		 * but this is not an error situation so make sure we
> > > 		 * return OK instead of BUF_ERROR at next call of deflate:
> > > 		 */
> > > 		s->last_flush = -1;
> > > 		return Z_OK;
> > > 	}
> > > }
> > 
> > Z_OK is actually an error, see crypto/deflate.c:
> 
> I saw Z_STREAM_END, but deflate states "this is not an error" and
> there are more places like this.

That would be a serious bug in deflate.  Where did you see it
return Z_STREAM_END in case of an overrun or error?

> So it will ENOSPC all errors, not sure how good that is.  We also
> have lz4/lz4hc that return the number of bytes "(((char *)op) - dest)"
> if successful and 0 otherwise.  So any error is 0. dst_buf overrun
> is also 0, impossible to tell the difference, again not sure if we
> can just ENOSPC.

I'm talking about the Crypto API calling convention.  Individual
compression libraries obviously have vastly different calling
conventions.

In the Crypto API, lz4 will return -EINVAL:

	int out_len = LZ4_compress_default(src, dst,
		slen, *dlen, ctx);

	if (!out_len)
		return -EINVAL;

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt