[PATCH 3/5] zram: recompression priority param should override algo

[Sergey Senozhatsky]

Recompression algorithm lookup by name is ambiguous and
can lead to unexpected results.  The problem is that
the system can configure the same algorithm but with
different parameters (compression level, C/D-dicts, etc.)
multiple times:

    [zstd clevel=3] [zstd clevel=8 dict=/etc/dict]

making it impossible to distinguish compressors by name.
It is advised to always use "priority".  Additionally,
override "algo" with "priority", when both params are
provided.

Suggested-by: Minchan Kim <minchan@xxxxxxxxxx>
Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
---
 drivers/block/zram/zram_drv.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 6ca5a76c3865..118b0b277e37 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -2594,6 +2594,16 @@ static ssize_t recompress_store(struct device *dev,
 			if (ret)
 				return ret;
 
+			/*
+			 * "priority" overrides "algo".
+			 *
+			 * We can have several algorithms configured with
+			 * different params (compression/acceleration level,
+			 * C/D-dict, etc.) but under the same name.
+			 *
+			 * "algorithm" name lookup is ambiguous.
+			 */
+			algo = NULL;
 			prio_max = min(prio + 1, ZRAM_MAX_COMPS);
 			continue;
 		}
-- 
2.53.0.473.g4a7958ca14-goog