[PATCH 2/2] zram: introduce automatic device_id generation

Sergey Senozhatsky
2015-03-04T14:16:33Z

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>
---
Documentation/ABI/testing/sysfs-class-zram | 7 +++++--
Documentation/blockdev/zram.txt | 10 ++++++++++
drivers/block/zram/zram_drv.c | 31 +++++++++++++++++++++++++++---
3 files changed, 43 insertions(+), 5 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-class-zram b/Documentation/ABI/testing/sysfs-class-zram
index 99b2a1e..0b678b2 100644
--- 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 4b140fa..6bbdded 100644
--- 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 0978307..e0b40bb 100644
--- 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;

@@ -1267,6 +1274,24 @@ 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,
@@ -1278,7 +1303,7 @@ 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,
};
--
2.3.1.167.g7f4ba4b