zram: add dynamic device add/remove functionality

We currently don't support on-demand device creation.  The only way to
have N zram devices is to specify num_devices module parameter (default
value 1).  That means that if, for some reason, at some point, user wants
to have N + 1 devies he/she must umount all the existing devices, unload
the module, load the module passing num_devices equals to N + 1.  And do
this again, if needed.

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>
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
new file mode 100644 (file)
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 7fcf9c6592ecc45d0765b7f1ae018228e8f758f7..4b140faade204bd4a53477f614db9bbaba3d4aef 100644 (file)
--- 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 bab8b20e3d345b1bc171467aafe945838d797b5e..a457e160c98f405dc12e532effd39abd8b8ba7f9 100644 (file)
--- 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;
        }