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

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Message-ID: <o7qvt25dxoxcxj5ec2tbf5y5nopi4mkiuklo63rnyc7bldxwdm@2l5lkllmaynk>
Date: Sun, 23 Feb 2025 13:02:41 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Herbert Xu <herbert@...dor.apana.org.au>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>, 
	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 (25/02/23 11:38), Herbert Xu wrote:
> 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?

Oh, sorry for the confusion, I was talking about Z_OK for overruns.

> > 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;

Right, so you said that for deflate it could be

       ret = zlib_deflate(stream, Z_FINISH);
       if (ret != Z_STREAM_END) {
               ret = -ENOSPC;          // and not -EINVAL
               goto out;
       }

if I understood it correctly.  Which would make it: return 0 on success
or -ENOSPC otherwise.  So if crypto API wants consistency and return -ENOSPC
for buffer overruns, then for lz4/lz4hc it also becomes binary: either 0 or
-ENOSCP.  Current -EINVAL return looks better to me, both for deflate and
for lz4/lz4hc.  -ENOSPC is an actionable error code, a user can double the
dst_out size and retry compression etc., while in reality it could be some
SW/HW issue that is misreported as -ENOSPC.



So re-iterating Barry's points:

> My point is:
> 1. All drivers must be capable of handling dst_buf overflow.

Not the case.

> 2. All drivers must return a consistent and dedicated error code for
> dst_buf overflow.

Not the case.