zram: propagate error to user

When we initialized zcomp with single, we couldn't change
max_comp_streams without zram reset but current interface doesn't show
any error to user and even it changes max_comp_streams's value without
any effect so it would make user very confusing.

This patch prevents max_comp_streams's change when zcomp was initialized
as single zcomp and emit the error to user(ex, echo).

[akpm@linux-foundation.org: don't return with the lock held, per Sergey]
[fengguang.wu@intel.com: fix coccinelle warnings]
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit 60a726e33375a1096e85399cfa1327081b4c38be)
Signed-off-by: Alex Shi <alex.shi@linaro.org>

diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 4ab2ce98f63caef028134e24614f0f1f6e010c12..2db1687a4b10766113bf82f371b22e966d4abc61 100644 (file)
--- a/Documentation/blockdev/zram.txt
+++ b/Documentation/blockdev/zram.txt
@@ -37,10 +37,11 @@ Note:
 In order to enable compression backend's multi stream support max_comp_streams
 must be initially set to desired concurrency level before ZRAM device
 initialisation. Once the device initialised as a single stream compression
-backend (max_comp_streams equals to 0) changing the value of max_comp_streams
-will not take any effect, because single stream compression backend implemented
-as a special case and does not support dynamic max_comp_streams. Only multi
-stream backend supports dynamic max_comp_streams adjustment.
+backend (max_comp_streams equals to 1), you will see error if you try to change
+the value of max_comp_streams because single stream compression backend
+implemented as a special case by lock overhead issue and does not support
+dynamic max_comp_streams. Only multi stream backend supports dynamic
+max_comp_streams adjustment.
 
 3) Select compression algorithm
        Using comp_algorithm device attribute one can see available and

diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
index 5647d8fe1dc177c302154df9497abc86ed68c0fc..b0e7592c44d85aaf32af0fcc302b29875d5a5e45 100644 (file)
--- a/drivers/block/zram/zcomp.c
+++ b/drivers/block/zram/zcomp.c
@@ -153,7 +153,7 @@ static void zcomp_strm_multi_release(struct zcomp *comp, struct zcomp_strm *zstr
 }
 
 /* change max_strm limit */
-static int zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
+static bool zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
 {
        struct zcomp_strm_multi *zs = comp->stream;
        struct zcomp_strm *zstrm;
@@ -172,7 +172,7 @@ static int zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
                zs->avail_strm--;
        }
        spin_unlock(&zs->strm_lock);
-       return 0;
+       return true;
 }
 
 static void zcomp_strm_multi_destroy(struct zcomp *comp)
@@ -232,10 +232,10 @@ static void zcomp_strm_single_release(struct zcomp *comp,
        mutex_unlock(&zs->strm_lock);
 }
 
-static int zcomp_strm_single_set_max_streams(struct zcomp *comp, int num_strm)
+static bool zcomp_strm_single_set_max_streams(struct zcomp *comp, int num_strm)
 {
        /* zcomp_strm_single support only max_comp_streams == 1 */
-       return -ENOTSUPP;
+       return false;
 }
 
 static void zcomp_strm_single_destroy(struct zcomp *comp)
@@ -284,7 +284,7 @@ ssize_t zcomp_available_show(const char *comp, char *buf)
        return sz;
 }
 
-int zcomp_set_max_streams(struct zcomp *comp, int num_strm)
+bool zcomp_set_max_streams(struct zcomp *comp, int num_strm)
 {
        return comp->set_max_streams(comp, num_strm);
 }

diff --git a/drivers/block/zram/zcomp.h b/drivers/block/zram/zcomp.h
index 8b8997f8613bd2d790c3eb26819b00bc10951e21..c59d1fca72c064d9990faf34dc1c95f1f9a807d1 100644 (file)
--- a/drivers/block/zram/zcomp.h
+++ b/drivers/block/zram/zcomp.h
@@ -46,7 +46,7 @@ struct zcomp {
 
        struct zcomp_strm *(*strm_find)(struct zcomp *comp);
        void (*strm_release)(struct zcomp *comp, struct zcomp_strm *zstrm);
-       int (*set_max_streams)(struct zcomp *comp, int num_strm);
+       bool (*set_max_streams)(struct zcomp *comp, int num_strm);
        void (*destroy)(struct zcomp *comp);
 };
 
@@ -64,5 +64,5 @@ int zcomp_compress(struct zcomp *comp, struct zcomp_strm *zstrm,
 int zcomp_decompress(struct zcomp *comp, const unsigned char *src,
                size_t src_len, unsigned char *dst);
 
-int zcomp_set_max_streams(struct zcomp *comp, int num_strm);
+bool zcomp_set_max_streams(struct zcomp *comp, int num_strm);
 #endif /* _ZCOMP_H_ */

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 407f541b26a16cbd85cb043354c9f0d3ccae471b..27da5967b57b6e88c9962232385e6c597697a360 100644 (file)
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -127,19 +127,28 @@ static ssize_t max_comp_streams_store(struct device *dev,
 {
        int num;
        struct zram *zram = dev_to_zram(dev);
+       int ret;
 
-       if (kstrtoint(buf, 0, &num))
-               return -EINVAL;
+       ret = kstrtoint(buf, 0, &num);
+       if (ret < 0)
+               return ret;
        if (num < 1)
                return -EINVAL;
+
        down_write(&zram->init_lock);
        if (init_done(zram)) {
-               if (zcomp_set_max_streams(zram->comp, num))
+               if (!zcomp_set_max_streams(zram->comp, num)) {
                        pr_info("Cannot change max compression streams\n");
+                       ret = -EINVAL;
+                       goto out;
+               }
        }
+
        zram->max_comp_streams = num;
+       ret = len;
+out:
        up_write(&zram->init_lock);
-       return len;
+       return ret;
 }
 
 static ssize_t comp_algorithm_show(struct device *dev,