[PATCH 5/8] zram: add dynamic device add/remove functionality

Sergey Senozhatsky
2015-03-03T12:49:57Z

Introduce zram-control sysfs class, which has two sysfs attrs:
- zram_add -- add a new specific (device_id) zram device
- zram_remove -- remove a specific (device_id) zram device

Usage example:
# add a new specific zram device
echo 4 > /sys/class/zram-control/zram_add

# remove a specific zram device
echo 4 > /sys/class/zram-control/zram_remove

There is no automatic device_id generation, so user is expected to
provide one.

NOTE, there might be users who already depend on the fact that at
least zram0 device gets always created by zram_init(). Thus, due to
compatibility reasons, along with requested device_id (f.e. 5) zram0
will also be created.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
Documentation/ABI/testing/sysfs-class-zram | 23 ++++++
Documentation/blockdev/zram.txt | 23 +++++-
drivers/block/zram/zram_drv.c | 120 +++++++++++++++++++++++++++++
3 files changed, 162 insertions(+), 4 deletions(-)
create mode 100644 Documentation/ABI/testing/sysfs-class-zram

diff --git a/Documentation/ABI/testing/sysfs-class-zram b/Documentation/ABI/testing/sysfs-class-zram
new file mode 100644
index 0000000..99b2a1e
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-zram
@@ -0,0 +1,23 @@
+What: /sys/class/zram-control/
+Date: March 2015
+KernelVersion: 4.1
+Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+ The zram-control/ class sub-directory belongs to zram
+ device class
+
+What: /sys/class/zram-control/zram_add
+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
+
+ What: /sys/class/zram-control/zram_add
+Date: March 2015
+KernelVersion: 4.1
+Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+ Remove a specific /dev/zramX device, where X is a device_id
+ provided by user
diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 7fcf9c6..4b140fa 100644
--- a/Documentation/blockdev/zram.txt
+++ b/Documentation/blockdev/zram.txt
@@ -19,7 +19,9 @@ Following shows a typical sequence of steps for using zram.
1) Load Module:
modprobe zram num_devices=4
This creates 4 devices: /dev/zram{0,1,2,3}
- (num_devices parameter is optional. Default: 1)
+
+num_devices parameter is optional and tells zram how many devices should be
+pre-created. Default: 1.

2) Set max number of compression streams
Compression backend may use up to max_comp_streams compression streams,
@@ -97,7 +99,20 @@ size of the disk when not in use so a huge zram is wasteful.
mkfs.ext4 /dev/zram1
mount /dev/zram1 /tmp

-7) Stats:
+7) Add/remove zram devices
+
+zram provides a control interface, which enables dynamic (on-demand) device
+addition and removal.
+
+In order to add a new /dev/zramX device (where X is a unique device id)
+execute
+ echo X > /sys/class/zram-control/zram_add
+
+To remove the existing /dev/zramX device (where X is a device id)
+execute
+ echo X > /sys/class/zram-control/zram_remove
+
+8) Stats:
Per-device statistics are exported as various nodes under
/sys/block/zram<id>/
disksize
@@ -113,11 +128,11 @@ size of the disk when not in use so a huge zram is wasteful.
mem_used_total
mem_used_max

-8) Deactivate:
+9) Deactivate:
swapoff /dev/zram0
umount /dev/zram1

-9) Reset:
+10) 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/zram_drv.c b/drivers/block/zram/zram_drv.c
index bab8b20..a457e16 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -33,16 +33,23 @@
#include <linux/vmalloc.h>
#include <linux/err.h>
#include <linux/idr.h>
+#include <linux/sysfs.h>

#include "zram_drv.h"

static DEFINE_IDR(zram_index_idr);
+/* idr index must be protected */
+static DEFINE_MUTEX(zram_index_mutex);
+
static int zram_major;
static const char *default_compressor = "lzo";

/* Module params (documentation at end) */
static unsigned int num_devices = 1;

+#define ZRAM_CTL_ADD 1
+#define ZRAM_CTL_REMOVE 2
+
#define ZRAM_ATTR_RO(name) \
static ssize_t name##_show(struct device *d, \
struct device_attribute *attr, char *b) \
@@ -1173,6 +1180,109 @@ static void zram_remove(struct zram *zram)
kfree(zram);
}

+/* lookup if there is any device pointer that match the given device_id.
+ * return device pointer if so, or ERR_PTR() otherwise. */
+static struct zram *zram_lookup(int dev_id)
+{
+ struct zram *zram;
+
+ zram = idr_find(&zram_index_idr, dev_id);
+ if (zram)
+ return zram;
+ return ERR_PTR(-ENODEV);
+}
+
+/* common zram-control add/remove handler */
+static int zram_control(int cmd, const char *buf)
+{
+ struct zram *zram;
+ int ret = -ENOSYS, err, dev_id;
+
+ /* dev_id is gendisk->first_minor, which is `int' */
+ ret = kstrtoint(buf, 10, &dev_id);
+ if (ret || dev_id < 0)
+ return ret;
+
+ mutex_lock(&zram_index_mutex);
+ zram = zram_lookup(dev_id);
+
+ switch (cmd) {
+ case ZRAM_CTL_ADD:
+ if (!IS_ERR(zram)) {
+ ret = -EEXIST;
+ break;
+ }
+ ret = zram_add(dev_id);
+ break;
+ case ZRAM_CTL_REMOVE:
+ if (IS_ERR(zram)) {
+ ret = PTR_ERR(zram);
+ break;
+ }
+
+ /* First, make ->disksize device attr RO, closing
+ * ZRAM_CTL_REMOVE vs disksize_store() race window */
+ ret = sysfs_chmod_file(&disk_to_dev(zram->disk)->kobj,
+ &dev_attr_disksize.attr, S_IRUGO);
+ if (ret)
+ break;
+
+ ret = zram_reset_device(zram);
+ if (ret == 0) {
+ /* ->disksize is RO and there are no ->bd_openers */
+ zram_remove(zram);
+ break;
+ }
+
+ /* If there are still device bd_openers, try to make ->disksize
+ * RW again and return. even if we fail to make ->disksize RW,
+ * user still has RW ->reset attr. so it's possible to destroy
+ * that device */
+ err = sysfs_chmod_file(&disk_to_dev(zram->disk)->kobj,
+ &dev_attr_disksize.attr,
+ S_IWUSR | S_IRUGO);
+ if (err)
+ ret = err;
+ break;
+ }
+ mutex_unlock(&zram_index_mutex);
+
+ return ret;
+}
+
+/* zram module control sysfs attributes */
+static ssize_t zram_add_store(struct class *class,
+ struct class_attribute *attr,
+ const char *buf,
+ size_t count)
+{
+ int ret = zram_control(ZRAM_CTL_ADD, buf);
+
+ return ret ? ret : count;
+}
+
+static ssize_t zram_remove_store(struct class *class,
+ struct class_attribute *attr,
+ const char *buf,
+ size_t count)
+{
+ int ret = zram_control(ZRAM_CTL_REMOVE, buf);
+
+ return ret ? ret : count;
+}
+
+static struct class_attribute zram_control_class_attrs[] = {
+ __ATTR_WO(zram_add),
+ __ATTR_WO(zram_remove),
+ __ATTR_NULL,
+};
+
+static struct class zram_control_class = {
+ .name = "zram-control",
+ .owner = THIS_MODULE,
+ .class_attrs = zram_control_class_attrs,
+};
+
static int zram_exit_cb(int id, void *ptr, void *data)
{
zram_remove(ptr);
@@ -1181,6 +1291,7 @@ static int zram_exit_cb(int id, void *ptr, void *data)

static void destroy_devices(void)
{
+ class_unregister(&zram_control_class);
idr_for_each(&zram_index_idr, &zram_exit_cb, NULL);
idr_destroy(&zram_index_idr);
unregister_blkdev(zram_major, "zram");
@@ -1197,14 +1308,23 @@ static int __init zram_init(void)
return -EINVAL;
}

+ ret = class_register(&zram_control_class);
+ if (ret) {
+ pr_warn("Unable to register zram-control class\n");
+ return ret;
+ }
+
zram_major = register_blkdev(0, "zram");
if (zram_major <= 0) {
pr_warn("Unable to get major number\n");
+ class_unregister(&zram_control_class);
return -EBUSY;
}

for (dev_id = 0; dev_id < num_devices; dev_id++) {
+ mutex_lock(&zram_index_mutex);
ret = zram_add(dev_id);
+ mutex_unlock(&zram_index_mutex);
if (ret != 0)
goto out_error;
}
--
2.3.1.167.g7f4ba4b