Hello Sergey,
I want to know more how it works so below questions goes.
On Wed, May 25, 2016 at 11:30:04PM +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().
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?
> 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?
> 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
So, when lzo module is loading?
>
> Signed-off-by: Sergey Senozhatsky <sergey.senozhat...@gmail.com>
> Cc: Minchan Kim <minc...@kernel.org>
> Cc: Joonsoo Kim <iamjoonsoo....@lge.com>
> ---
> drivers/block/zram/zcomp.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
> index 79b30d7..a8593e9 100644
> --- a/drivers/block/zram/zcomp.c
> +++ b/drivers/block/zram/zcomp.c
> @@ -29,12 +29,16 @@ static const char * const backends[] = {
> static const char *find_backend(const char *compress)
> {
> int i = 0;
> +
> while (backends[i]) {
> if (sysfs_streq(compress, backends[i]))
> break;
> i++;
> }
> - return backends[i];
> +
> + if (backends[i] && crypto_has_comp(backends[i], 0, 0))
> + return backends[i];
> + return NULL;
> }
>
> static void zcomp_strm_free(struct zcomp *comp, struct zcomp_strm *zstrm)
> @@ -74,14 +78,16 @@ ssize_t zcomp_available_show(const char *comp, char *buf)
> ssize_t sz = 0;
> int i = 0;
>
> - while (backends[i]) {
> + for (; backends[i]; i++) {
> + if (!crypto_has_comp(backends[i], 0, 0))
> + continue;
> +
> if (!strcmp(comp, backends[i]))
> sz += scnprintf(buf + sz, PAGE_SIZE - sz - 2,
> "[%s] ", backends[i]);
> else
> sz += scnprintf(buf + sz, PAGE_SIZE - sz - 2,
> "%s ", backends[i]);
> - i++;
> }
> sz += scnprintf(buf + sz, PAGE_SIZE - sz, "\n");
> return sz;
> --
> 2.8.3.394.g3916adf
>
