zram: introduce automatic device_id generation

The existing device creation interface requires user to provide new and
unique device_id for every device being created.  This might be difficult
to handle (f.e.  in automated scripts).

Extend zram-control/zram_add interface to support read and write
operations.  Write operation remains the same:

	echo X > /sys/class/zram-control/zram_add

will add /dev/zramX (or return error).

Read operation is treated as 'pick up available device_id, add new device
and return device_id'.

Example:
	 cat /sys/class/zram-control/zram_add
	2
	 cat /sys/class/zram-control/zram_add
	3

so user-space can proceed with /dev/zram2, /dev/zram3 init and usage.

An attempt to use already used device_id (-EEXIST)

	echo 3 > /sys/class/zram-control/zram_add
	-bash: echo: write error: File exists

Returning zram_add error code back to user (-ENOMEM in this case)

	cat /sys/class/zram-control/zram_add
	cat: /sys/class/zram-control/zram_add: Cannot allocate memory

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/Documentation/ABI/testing/sysfs-class-zram b/Documentation/ABI/testing/sysfs-class-zram
index 99b2a1e422e013383ca8529be4770253282ae0d0..0b678b28ad09ddacb40e83919cced42a877925c3 100644 (file)
--- a/Documentation/ABI/testing/sysfs-class-zram
+++ b/Documentation/ABI/testing/sysfs-class-zram
@@ -11,8 +11,11 @@ Date:                March 2015
 KernelVersion: 4.1
 Contact:       Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
 Description:
-               Add a specific /dev/zramX device, where X is a device_id
-               provided by user
+               RW attribuite. Write operation adds a specific /dev/zramX
+               device, where X is a device_id provided by user.
+               Read operation will automatically pick up avilable device_id
+               X, add /dev/zramX device and return that device_id X back to
+               user.
 
                What:           /sys/class/zram-control/zram_add
 Date:          March 2015

diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 4b140faade204bd4a53477f614db9bbaba3d4aef..6bbddedf10e517f53948aff50fb5d86a7d23065a 100644 (file)
--- a/Documentation/blockdev/zram.txt
+++ b/Documentation/blockdev/zram.txt
@@ -112,6 +112,16 @@ To remove the existing /dev/zramX device (where X is a device id)
 execute
        echo X > /sys/class/zram-control/zram_remove
 
+Additionally, zram also handles automatic device_id generation and assignment.
+
+       cat /sys/class/zram-control/zram_add
+       1
+       cat /sys/class/zram-control/zram_add
+       2
+
+this will pick up available device_id X, add corresponding /dev/zramX
+device and return its device_id X back to user (or error code).
+
 8) Stats:
        Per-device statistics are exported as various nodes under
        /sys/block/zram<id>/

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 73d03d16d92d0192a1134ac2d792c3251c001364..820a29e911f483bba9a4ca49f2b0f794580a6960 100644 (file)
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1078,8 +1078,15 @@ static int zram_add(int device_id)
        if (!zram)
                return ret;
 
-       ret = idr_alloc(&zram_index_idr, zram, device_id,
-                       device_id + 1, GFP_KERNEL);
+       if (device_id < 0) {
+               /* generate new device_id */
+               ret = idr_alloc(&zram_index_idr, zram, 0, 0, GFP_KERNEL);
+               device_id = ret;
+       } else {
+               /* use provided device_id */
+               ret = idr_alloc(&zram_index_idr, zram, device_id,
+                               device_id + 1, GFP_KERNEL);
+       }
        if (ret < 0)
                goto out_free_dev;
 
@@ -1271,6 +1278,24 @@ static ssize_t zram_add_store(struct class *class,
        return ret ? ret : count;
 }
 
+static ssize_t zram_add_show(struct class *class,
+                       struct class_attribute *attr,
+                       char *buf)
+{
+       int ret;
+
+       mutex_lock(&zram_index_mutex);
+       /* read operation on zram_add is - pick up device_id
+        * automatically, add corresponding device and return
+        * that device_id back to user */
+       ret = zram_add(-1);
+       mutex_unlock(&zram_index_mutex);
+
+       if (ret < 0)
+               return ret;
+       return scnprintf(buf, PAGE_SIZE, "%d\n", ret);
+}
+
 static ssize_t zram_remove_store(struct class *class,
                        struct class_attribute *attr,
                        const char *buf,
@@ -1282,7 +1307,7 @@ static ssize_t zram_remove_store(struct class *class,
 }
 
 static struct class_attribute zram_control_class_attrs[] = {
-       __ATTR_WO(zram_add),
+       __ATTR_RW(zram_add),
        __ATTR_WO(zram_remove),
        __ATTR_NULL,
 };