From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932544AbcE0HvF (ORCPT ); Fri, 27 May 2016 03:51:05 -0400 Received: from mail-pa0-f68.google.com ([209.85.220.68]:34322 "EHLO mail-pa0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932077AbcE0HvD (ORCPT ); Fri, 27 May 2016 03:51:03 -0400 Date: Fri, 27 May 2016 16:50:52 +0900 From: Sergey Senozhatsky To: Minchan Kim Cc: Sergey Senozhatsky , Andrew Morton , Joonsoo Kim , linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: Re: [PATCH 5/7] zram: use crypto api to check alg availability Message-ID: <20160527075052.GB504@swordfish> References: <20160525143006.1207-1-sergey.senozhatsky@gmail.com> <20160525143006.1207-6-sergey.senozhatsky@gmail.com> <20160527044343.GE2322@bbox> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160527044343.GE2322@bbox> User-Agent: Mutt/1.6.1 (2016-04-27) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (05/27/16 13:43), Minchan Kim wrote: [..] > > modprobe zram > > cat /proc/crypto | grep -i lz4 > > modprobe lz4 > > cat /proc/crypto | grep -i lz4 > > name : lz4 > > driver : lz4-generic > > module : lz4 > > > > So the user can't tell exactly if the lz4 is really supported > > from /proc/crypto output, unless someone or something has loaded > > it. > > > > This patch also adds crypto_has_comp() to zcomp_available_show(). > > crypto_has_comp works regardless of that whether module is loading or not? > IOW, currently, if lz4 modules is not loading, but crypto_has_comp return > true about lz4 module. > Right? correct. crypto_has_comp() regardless the module being loaded. # modprobe zram # cat /proc/crypto | egrep -e "lzo|lz4|deflate" # echo lzo > /sys/block/zram0/comp_algorithm # cat /proc/crypto | egrep -e "lzo|lz4|deflate" name : lzo driver : lzo-generic module : lzo # echo lz4 > /sys/block/zram0/comp_algorithm # cat /proc/crypto | egrep -e "lzo|lz4|deflate" name : lz4 driver : lz4-generic module : lz4 name : lzo driver : lzo-generic module : lzo # echo deflate > /sys/block/zram0/comp_algorithm # cat /proc/crypto | egrep -e "lzo|lz4|deflate" name : deflate driver : deflate-generic module : deflate name : lz4 driver : lz4-generic module : lz4 name : lzo driver : lzo-generic module : lzo what is does, tho, it modprobs() the module upon the first request: crypto_has_comp(...) crypto_has_alg() crypto_alg_mod_lookup() crypto_larval_lookup() request_module("crypto-%s", name) __request_module() call_modprobe() and this is when /proc/crypto is getting updated. otherwise user has no information (well, unless modules were loaded by something/someome else, or crypto compressors were built-in into the kernel). I'm not aware of any other way to achieve this functionality for zram. > > We store all the compression algorithms names in zcomp's `backends' > > array, regardless the CONFIG_CRYPTO_FOO configuration, but show > > Then, you mean we should add new string into backend array whenever > adding new crypto compatible compression algorithm? yes. which looks quite trivial: adding or removing a string to/from the array. > > cat /proc/crypto | grep -i lz4 > > > > cat /sys/block/zram0/comp_algorithm > > [lzo] lz4 deflate lz4hc 842 > > So, when lzo module is loading? when we execute crypto_has_comp("lzo") for the first time. that's why doing just # modprobe zram will not cause /proc/crypto update # modprobe zram # cat /proc/crypto | egrep -e "lzo|lz4|deflate" crypto_has_comp() updates it -- when we read or write from/to comp_algorithm: # cat /sys/block/zram0/comp_algorithm [lzo] lz4 deflate lz4hc 842 # cat /proc/crypto | egrep -e "lzo|lz4|deflate" name : lzo driver : lzo-generic module : lzo but I didn't want zram to depend on this, or to depend on /proc/crypto content; that's why I did it the way it is. -ss