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authorSergey Senozhatsky <sergey.senozhatsky@gmail.com>2016-07-26 15:22:48 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-07-26 16:19:19 -0700
commit415403be37e204632b17bdb6857890fe5a220cea (patch)
tree994757df320bc700b01ea86fa458a071f925ae58 /Documentation/blockdev
parentebaf9ab56d9d5f350969bd1ea8f47234623c9684 (diff)
zram: use crypto api to check alg availability
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). [sergey.senozhatsky@gmail.com: zram-use-crypto-api-to-check-alg-availability-v3] Link: http://lkml.kernel.org/r/20160604024902.11778-4-sergey.senozhatsky@gmail.com Link: http://lkml.kernel.org/r/20160531122017.2878-5-sergey.senozhatsky@gmail.com Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/blockdev')
-rw-r--r--Documentation/blockdev/zram.txt11
1 files changed, 11 insertions, 0 deletions
diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 13100fb3c26d..7c05357360a7 100644
--- a/Documentation/blockdev/zram.txt
+++ b/Documentation/blockdev/zram.txt
@@ -83,6 +83,17 @@ pre-created. Default: 1.
#select lzo compression algorithm
echo lzo > /sys/block/zram0/comp_algorithm
+ For the time being, the `comp_algorithm' content does not necessarily
+ show every compression algorithm supported by the kernel. We keep this
+ list primarily to simplify device configuration and one can configure
+ a new device with a compression algorithm that is not listed in
+ `comp_algorithm'. The thing is that, internally, ZRAM uses Crypto API
+ and, if some of the algorithms were built as modules, it's impossible
+ to list all of them using, for instance, /proc/crypto or any other
+ method. This, however, has an advantage of permitting the usage of
+ custom crypto compression modules (implementing S/W or H/W
+ compression).
+
4) Set Disksize
Set disk size by writing the value to sysfs node 'disksize'.
The value can be either in bytes or you can use mem suffixes.