netdev - Re: [v4 PATCH 10/13] ubifs: Use crypto

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Message-ID: <Z9VEkEOul9bt4bc1@gondor.apana.org.au>
Date: Sat, 15 Mar 2025 17:12:48 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Zhihao Cheng <chengzhihao1@...wei.com>
Cc: Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
	Richard Weinberger <richard@....at>, linux-mtd@...ts.infradead.org,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Pavel Machek <pavel@....cz>, linux-pm@...r.kernel.org,
	Steffen Klassert <steffen.klassert@...unet.com>,
	netdev@...r.kernel.org
Subject: Re: [v4 PATCH 10/13] ubifs: Use crypto_acomp interface

On Sat, Mar 15, 2025 at 05:08:47PM +0800, Zhihao Cheng wrote:
>
> According to the warning message, current compressor is zstd. The output
> buffer size is limited only for LZO compressor by [1].

Any algorithm can and will produce output longer than the input,
if you give it enough output buffer.

Previously an output buffer length of 2x the input length was given
to all algorithms, meaning that they would all succeed no matter
whether the input can be compressed or not.

This has now been changed so that incompressible data is not
needlessly compressed all the way to the end.  In fact we should
reduce it further to eliminate the UBIFS_MIN_COMPRESS_DIFF check.

I will remove the warning on compression since failures are
expected and reduce the output buffer length further to remove
the post-compression length check.

Thanks,
-- 
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