We currently don't support on-demand device creation. The one and 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.
This patch introduces zram control sysfs class, which has two sysfs attrs: - zram_add -- add a new zram device - zram_remove -- remove a specific (device_id) zram device zram_add sysfs attr is read-only and has only automatic device id assignment mode (as requested by Minchan Kim). read operation performed on this attr creates a new zram device and returns back its device_id or error status. Usage example: # add a new specific zram device cat /sys/class/zram-control/zram_add 2 # remove a specific zram device echo 4 > /sys/class/zram-control/zram_remove 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 NOTE, there might be users who already depend on the fact that at least zram0 device gets always created by zram_init(). Preserve this behavior. [Andrew Morton <a...@linux-foundation.org>: fix comment layout] Reported-by: Minchan Kim <minc...@kernel.org> Signed-off-by: Sergey Senozhatsky <sergey.senozhat...@gmail.com> --- Documentation/ABI/testing/sysfs-class-zram | 24 ++++++ Documentation/blockdev/zram.txt | 23 +++++- drivers/block/zram/zram_drv.c | 124 ++++++++++++++++++++++++++++- 3 files changed, 166 insertions(+), 5 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..6f62ef5 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-class-zram @@ -0,0 +1,24 @@ +What: /sys/class/zram-control/ +Date: August 2015 +KernelVersion: 4.1 +Contact: Sergey Senozhatsky <sergey.senozhat...@gmail.com> +Description: + The zram-control/ class sub-directory belongs to zram + device class + +What: /sys/class/zram-control/zram_add +Date: August 2015 +KernelVersion: 4.1 +Contact: Sergey Senozhatsky <sergey.senozhat...@gmail.com> +Description: + RO attribute. Read operation will cause zram to add a new + device and return its device id back to user (so one can + use /dev/zram<id>), or error code. + +What: /sys/class/zram-control/zram_add +Date: August 2015 +KernelVersion: 4.1 +Contact: Sergey Senozhatsky <sergey.senozhat...@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 2ccc741..44b1a77 100644 --- a/Documentation/blockdev/zram.txt +++ b/Documentation/blockdev/zram.txt @@ -99,7 +99,24 @@ 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, perform read operation on zram_add +attribute. This will return either new device's device id (meaning that you +can use /dev/zram<id>) or error code. + +Example: + cat /sys/class/zram-control/zram_add + 1 + +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>/ A brief description of exported device attritbutes. For more details please @@ -178,11 +195,11 @@ line of text and contains the following stats separated by whitespace: num_migrated -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 2c2e7cc..848222a 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -33,10 +33,14 @@ #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"; @@ -1168,8 +1172,15 @@ static int zram_add(int device_id) if (!zram) return -ENOMEM; - 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; @@ -1278,6 +1289,105 @@ 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); +} + +/* zram module control sysfs attributes */ +static ssize_t zram_add_show(struct class *class, + struct class_attribute *attr, + char *buf) +{ + int ret; + + mutex_lock(&zram_index_mutex); + /* pick up available device_id */ + 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, + size_t count) +{ + struct zram *zram; + int ret, err, dev_id; + + mutex_lock(&zram_index_mutex); + + /* dev_id is gendisk->first_minor, which is `int' */ + ret = kstrtoint(buf, 10, &dev_id); + if (ret || dev_id < 0) { + ret = -EINVAL; + goto out; + } + + zram = zram_lookup(dev_id); + if (IS_ERR(zram)) { + ret = PTR_ERR(zram); + goto out; + } + + /* + * First, make ->disksize device attr RO, closing + * zram_remove() vs disksize_store() race window + */ + ret = sysfs_chmod_file(&disk_to_dev(zram->disk)->kobj, + &dev_attr_disksize.attr, S_IRUGO); + if (ret) + goto out; + + ret = zram_reset_device(zram); + if (ret == 0) { + /* ->disksize is RO and there are no ->bd_openers */ + zram_remove(zram); + goto out; + } + + /* + * 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; + +out: + mutex_unlock(&zram_index_mutex); + return ret ? ret : count; +} + +static struct class_attribute zram_control_class_attrs[] = { + __ATTR_RO(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); @@ -1286,6 +1396,7 @@ 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"); @@ -1295,14 +1406,23 @@ static int __init zram_init(void) { int ret, dev_id; + 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; } -- 2.4.0.rc2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/