Messages in this thread | | | Date | Fri, 27 May 2016 16:50:52 +0900 | From | Sergey Senozhatsky <> | Subject | Re: [PATCH 5/7] zram: use crypto api to check alg availability |
| |
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
| |