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
