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SubjectRe: [PATCH v3 3/7] zram: use crypto api to check alg availability
On Sat, Jun 04, 2016 at 11:48:58AM +0900, Sergey Senozhatsky wrote:
> There is no way to get a string with all the crypto comp
> algorithms supported by the crypto comp engine, so we need
> to maintain our own backends list. At the same time we
> additionally need to use crypto_has_comp() to make sure
> that the user has requested a compression algorithm that is
> recognized by the crypto comp engine. Relying on /proc/crypto
> is not an options here, because it does not show not-yet-inserted
> compression modules.
>
> Example:
>
> 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().
> We store all the compression algorithms names in zcomp's `backends'
> array, regardless the CONFIG_CRYPTO_FOO configuration, but show
> only those that are also supported by crypto engine. This helps
> user to know the exact list of compression algorithms that can be
> used.
>
> Example:
> module lz4 is not loaded yet, but is supported by the crypto
> engine. /proc/crypto has no information on this module, while
> zram's `comp_algorithm' lists it:
>
> cat /proc/crypto | grep -i lz4
>
> cat /sys/block/zram0/comp_algorithm
> [lzo] lz4 deflate lz4hc 842
>
> We still use the `backends' array to determine if the requested
> compression backend is known to crypto api. This array, however,
> may not contain some entries, therefore as the last step we call
> crypto_has_comp() function which attempts to insmod the requested
> compression algorithm to determine if crypto api supports it. The
> advantage of this method is that now we permit the usage of
> out-of-tree crypto compression modules (implementing S/W or H/W
> compression).
>
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>

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