zram: make compression algorithm selection possible

Add and document `comp_algorithm' device attribute.  This attribute allows
to show supported compression and currently selected compression
algorithms:

	cat /sys/block/zram0/comp_algorithm
	[lzo] lz4

and change selected compression algorithm:
	echo lzo > /sys/block/zram0/comp_algorithm

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

6 files changed, 93 insertions, 11 deletions

diff --git a/Documentation/ABI/testing/sysfs-block-zram b/Documentation/ABI/testing/sysfs-block-zram
index 0da9ed6b82ea..70ec992514d0 100644
--- a/Documentation/ABI/testing/sysfs-block-zram
+++ b/Documentation/ABI/testing/sysfs-block-zram
@@ -65,6 +65,14 @@ Description:
                 number of backend's zcomp_strm compression streams (number of
                 concurrent compress operations).
 
+What:           /sys/block/zram<id>/comp_algorithm
+Date:           February 2014
+Contact:        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+                The comp_algorithm file is read-write and lets to show
+                available and selected compression algorithms, change
+                compression algorithm selection.
+
 What:           /sys/block/zram<id>/notify_free
 Date:           August 2010
 Contact:        Nitin Gupta <ngupta@vflare.org>
diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index aadfe60391b7..2604ffed51db 100644
--- a/Documentation/blockdev/zram.txt
+++ b/Documentation/blockdev/zram.txt
@@ -42,7 +42,21 @@ 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.
 
-3) Set Disksize
+3) Select compression algorithm
+        Using comp_algorithm device attribute one can see available and
+        currently selected (shown in square brackets) compression algortithms,
+        change selected compression algorithm (once the device is initialised
+        there is no way to change compression algorithm).
+
+        Examples:
+        #show supported compression algorithms
+        cat /sys/block/zram0/comp_algorithm
+        lzo [lz4]
+
+        #select lzo compression algorithm
+        echo lzo > /sys/block/zram0/comp_algorithm
+
+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.
         Examples:
@@ -59,14 +73,14 @@ There is little point creating a zram of greater than twice the size of memory
 since we expect a 2:1 compression ratio. Note that zram uses about 0.1% of the
 size of the disk when not in use so a huge zram is wasteful.
 
-4) Activate:
+5) Activate:
         mkswap /dev/zram0
         swapon /dev/zram0
 
         mkfs.ext4 /dev/zram1
         mount /dev/zram1 /tmp
 
-5) Stats:
+6) Stats:
         Per-device statistics are exported as various nodes under
         /sys/block/zram<id>/
                 disksize
@@ -81,11 +95,11 @@ size of the disk when not in use so a huge zram is wasteful.
                 compr_data_size
                 mem_used_total
 
-6) Deactivate:
+7) Deactivate:
         swapoff /dev/zram0
         umount /dev/zram1
 
-7) Reset:
+8) Reset:
         Write any positive value to 'reset' sysfs node
         echo 1 > /sys/block/zram0/reset
         echo 1 > /sys/block/zram1/reset
diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
index ac276f79f21c..aad533a8bc55 100644
--- a/drivers/block/zram/zcomp.c
+++ b/drivers/block/zram/zcomp.c
@@ -39,11 +39,20 @@ struct zcomp_strm_multi {
         wait_queue_head_t strm_wait;
 };
 
+static struct zcomp_backend *backends[] = {
+        &zcomp_lzo,
+        NULL
+};
+
 static struct zcomp_backend *find_backend(const char *compress)
 {
-        if (strncmp(compress, "lzo", 3) == 0)
-                return &zcomp_lzo;
-        return NULL;
+        int i = 0;
+        while (backends[i]) {
+                if (sysfs_streq(compress, backends[i]->name))
+                        break;
+                i++;
+        }
+        return backends[i];
 }
 
 static void zcomp_strm_free(struct zcomp *comp, struct zcomp_strm *zstrm)
@@ -251,6 +260,23 @@ static int zcomp_strm_single_create(struct zcomp *comp)
         return 0;
 }
 
+/* show available compressors */
+ssize_t zcomp_available_show(const char *comp, char *buf)
+{
+        ssize_t sz = 0;
+        int i = 0;
+
+        while (backends[i]) {
+                if (sysfs_streq(comp, backends[i]->name))
+                        sz += sprintf(buf + sz, "[%s] ", backends[i]->name);
+                else
+                        sz += sprintf(buf + sz, "%s ", backends[i]->name);
+                i++;
+        }
+        sz += sprintf(buf + sz, "\n");
+        return sz;
+}
+
 int 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 bd11d59c5dd1..8b8997f8613b 100644
--- a/drivers/block/zram/zcomp.h
+++ b/drivers/block/zram/zcomp.h
@@ -50,6 +50,8 @@ struct zcomp {
         void (*destroy)(struct zcomp *comp);
 };
 
+ssize_t zcomp_available_show(const char *comp, char *buf);
+
 struct zcomp *zcomp_create(const char *comp, int max_strm);
 void zcomp_destroy(struct zcomp *comp);
 
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 3a5f24c341dc..15d46f2e158c 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -141,6 +141,34 @@ static ssize_t max_comp_streams_store(struct device *dev,
         return len;
 }
 
+static ssize_t comp_algorithm_show(struct device *dev,
+                struct device_attribute *attr, char *buf)
+{
+        size_t sz;
+        struct zram *zram = dev_to_zram(dev);
+
+        down_read(&zram->init_lock);
+        sz = zcomp_available_show(zram->compressor, buf);
+        up_read(&zram->init_lock);
+
+        return sz;
+}
+
+static ssize_t comp_algorithm_store(struct device *dev,
+                struct device_attribute *attr, const char *buf, size_t len)
+{
+        struct zram *zram = dev_to_zram(dev);
+        down_write(&zram->init_lock);
+        if (init_done(zram)) {
+                up_write(&zram->init_lock);
+                pr_info("Can't change algorithm for initialized device\n");
+                return -EBUSY;
+        }
+        strlcpy(zram->compressor, buf, sizeof(zram->compressor));
+        up_write(&zram->init_lock);
+        return len;
+}
+
 /* flag operations needs meta->tb_lock */
 static int zram_test_flag(struct zram_meta *meta, u32 index,
                         enum zram_pageflags flag)
@@ -572,10 +600,10 @@ static ssize_t disksize_store(struct device *dev,
                 goto out_free_meta;
         }
 
-        zram->comp = zcomp_create(default_compressor, zram->max_comp_streams);
+        zram->comp = zcomp_create(zram->compressor, zram->max_comp_streams);
         if (!zram->comp) {
                 pr_info("Cannot initialise %s compressing backend\n",
-                                default_compressor);
+                                zram->compressor);
                 err = -EINVAL;
                 goto out_free_meta;
         }
@@ -735,6 +763,8 @@ static DEVICE_ATTR(orig_data_size, S_IRUGO, orig_data_size_show, NULL);
 static DEVICE_ATTR(mem_used_total, S_IRUGO, mem_used_total_show, NULL);
 static DEVICE_ATTR(max_comp_streams, S_IRUGO | S_IWUSR,
                 max_comp_streams_show, max_comp_streams_store);
+static DEVICE_ATTR(comp_algorithm, S_IRUGO | S_IWUSR,
+                comp_algorithm_show, comp_algorithm_store);
 
 ZRAM_ATTR_RO(num_reads);
 ZRAM_ATTR_RO(num_writes);
@@ -760,6 +790,7 @@ static struct attribute *zram_disk_attrs[] = {
         &dev_attr_compr_data_size.attr,
         &dev_attr_mem_used_total.attr,
         &dev_attr_max_comp_streams.attr,
+        &dev_attr_comp_algorithm.attr,
         NULL,
 };
 
@@ -820,7 +851,7 @@ static int create_device(struct zram *zram, int device_id)
                 pr_warn("Error creating sysfs group");
                 goto out_free_disk;
         }
-
+        strlcpy(zram->compressor, default_compressor, sizeof(zram->compressor));
         zram->meta = NULL;
         zram->max_comp_streams = 1;
         return 0;
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index ccf36d11755a..7f21c145e317 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -101,5 +101,6 @@ struct zram {
         u64 disksize;   /* bytes */
         int max_comp_streams;
         struct zram_stats stats;
+        char compressor[10];
 };
 #endif