[PATCH] zram: propagate error to user

[Minchan Kim]

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).

Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
 Documentation/blockdev/zram.txt |  9 +++++----
 drivers/block/zram/zcomp.c      | 10 +++++-----
 drivers/block/zram/zcomp.h      |  4 ++--
 drivers/block/zram/zram_drv.c   | 15 +++++++++++----
 4 files changed, 23 insertions(+), 15 deletions(-)

diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 2604ffed51db..0595c3f56ccf 100644
--- 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 92a83df40a27..15fe6a27781b 100644
--- a/drivers/block/zram/zcomp.c
+++ b/drivers/block/zram/zcomp.c
@@ -152,7 +152,7 @@ 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;
@@ -171,7 +171,7 @@ 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)
@@ -231,10 +231,10 @@ 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 0;
 }
 
 static void zcomp_strm_single_destroy(struct zcomp *comp)
@@ -283,7 +283,7 @@ 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 8b8997f8613b..c59d1fca72c0 100644
--- 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 7631ef0cbc41..eead9db9b100 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -128,17 +128,24 @@ static ssize_t max_comp_streams_store(struct device *dev,
 	struct zram *zram = dev_to_zram(dev);
 
 	if (kstrtoint(buf, 0, &num))
-		return -EINVAL;
+		goto out;
 	if (num < 1)
-		return -EINVAL;
+		goto out;
+
 	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");
+			goto out_unlock;
+		}
 	}
+
 	zram->max_comp_streams = num;
-	up_write(&zram->init_lock);
 	return len;
+out_unlock:
+	up_write(&zram->init_lock);
+out:
+	return -EINVAL;
 }
 
 static ssize_t comp_algorithm_show(struct device *dev,
-- 
1.9.0

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