Introduce /dev/zram-control interface which lets user-space to add a new zram device (ZRAM_CTL_ADD ioctl) or remove the existing one (ZRAM_CTL_REMOVE ioctl).
This patch adds only two ioctl operations: add device and remove device. There is no support for `automatic' device_id generation in this patch (will come up later), so correct device_id must be provided. Corresponding user-space visible defines (ZRAM_CTL_ADD/ZRAM_CTL_REMOVE) are located in a new header file: include/uapi/linux/zram.h. Well, we have `private' zram_drv.h and `public' zram.h headers from now on. I don't really want to make zram_drv.h public, that would require moving of all private defines and structs to zram_drv.c (100+ lines of code) and zram_drv.c is already big and a bit complicated. On the other hand, zram uses struct block_device_operations that has a per-device ->ioctl callback (not used by zram as of now). Ideally, we can drop some of the existing zram_stats sysfs device ATTRs and use ioctl (f.e. ZRAM_CTL_INFO) to copy out zram->stats to user-space. That will require zram_info structure being visible to user-space via zram.h, so this new header file can be of use. Interface usage example (pretty much like LOOP ctl interface): #include <linux/zram.h> cfd = open("/dev/zram-control", O_RDWR); /* add a new specific zram device */ err = ioctl(cfd, ZRAM_CTL_ADD, devnr); /* remove a specific zram device */ err = ioctl(cfd, ZRAM_CTL_REMOVE, devnr); NOTE, zram provides /dev/zram-control alias and zram module will be loaded automatically when /dev/zram-control is access the first time. However, 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. ZRAM_CTL_ADD 5) zram0 will also be created. Signed-off-by: Sergey Senozhatsky <sergey.senozhat...@gmail.com> --- drivers/block/zram/zram_drv.c | 99 ++++++++++++++++++++++++++++++++++++++++++- include/linux/miscdevice.h | 1 + include/uapi/linux/Kbuild | 1 + include/uapi/linux/zram.h | 17 ++++++++ 4 files changed, 117 insertions(+), 1 deletion(-) create mode 100644 include/uapi/linux/zram.h diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 92087da..4f87d1e 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -33,10 +33,15 @@ #include <linux/vmalloc.h> #include <linux/err.h> #include <linux/idr.h> +#include <linux/miscdevice.h> +#include <linux/zram.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"; @@ -1060,6 +1065,19 @@ static struct attribute_group zram_disk_attr_group = { .attrs = zram_disk_attrs, }; +/* lookup if there is any device pointer that match to 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); +} + static int zram_add(int device_id) { struct zram *zram; @@ -1174,6 +1192,76 @@ static void zram_remove(struct zram *zram) kfree(zram); } +static long zram_control_ioctl(struct file *file, unsigned int cmd, + unsigned long parm) +{ + struct zram *zram; + int ret = -ENOSYS, err; + + mutex_lock(&zram_index_mutex); + zram = zram_lookup(parm); + + switch (cmd) { + case ZRAM_CTL_ADD: + if (!IS_ERR(zram)) { + ret = -EEXIST; + break; + } + ret = zram_add(parm); + 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; +} + +static const struct file_operations zram_ctl_fops = { + .open = nonseekable_open, + .unlocked_ioctl = zram_control_ioctl, + .compat_ioctl = zram_control_ioctl, + .owner = THIS_MODULE, + .llseek = noop_llseek, +}; + +static struct miscdevice zram_misc = { + .minor = ZRAM_CTRL_MINOR, + .name = "zram-control", + .fops = &zram_ctl_fops, +}; + +MODULE_ALIAS_MISCDEV(ZRAM_CTRL_MINOR); +MODULE_ALIAS("devname:zram-control"); + static int zram_exit_cb(int id, void *ptr, void *data) { zram_remove(ptr); @@ -1182,6 +1270,7 @@ static int zram_exit_cb(int id, void *ptr, void *data) static void destroy_devices(void) { + misc_deregister(&zram_misc); idr_for_each(&zram_index_idr, &zram_exit_cb, NULL); idr_destroy(&zram_index_idr); unregister_blkdev(zram_major, "zram"); @@ -1198,6 +1287,12 @@ static int __init zram_init(void) return -EINVAL; } + ret = misc_register(&zram_misc); + if (ret < 0) { + pr_warn("Unable to register zram-control\n"); + return ret; + } + zram_major = register_blkdev(0, "zram"); if (zram_major <= 0) { pr_warn("Unable to get major number\n"); @@ -1205,7 +1300,9 @@ static int __init zram_init(void) } 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; } @@ -1227,7 +1324,7 @@ module_init(zram_init); module_exit(zram_exit); module_param(num_devices, uint, 0); -MODULE_PARM_DESC(num_devices, "Number of zram devices"); +MODULE_PARM_DESC(num_devices, "Number of pre-created zram devices"); MODULE_LICENSE("Dual BSD/GPL"); MODULE_AUTHOR("Nitin Gupta <ngu...@vflare.org>"); diff --git a/include/linux/miscdevice.h b/include/linux/miscdevice.h index ee80dd7..11a14e3 100644 --- a/include/linux/miscdevice.h +++ b/include/linux/miscdevice.h @@ -49,6 +49,7 @@ #define LOOP_CTRL_MINOR 237 #define VHOST_NET_MINOR 238 #define UHID_MINOR 239 +#define ZRAM_CTRL_MINOR 240 #define MISC_DYNAMIC_MINOR 255 struct device; diff --git a/include/uapi/linux/Kbuild b/include/uapi/linux/Kbuild index 68ceb97..9cabde9 100644 --- a/include/uapi/linux/Kbuild +++ b/include/uapi/linux/Kbuild @@ -448,3 +448,4 @@ header-y += xattr.h header-y += xfrm.h header-y += zorro.h header-y += zorro_ids.h +header-y += zram.h diff --git a/include/uapi/linux/zram.h b/include/uapi/linux/zram.h new file mode 100644 index 0000000..7b84532 --- /dev/null +++ b/include/uapi/linux/zram.h @@ -0,0 +1,17 @@ +/* + * include/linux/zram.h + * + * Copyright (C) 2015 Sergey Senozhatsky. + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + */ +#ifndef _UAPI_LINUX_ZRAM_H +#define _UAPI_LINUX_ZRAM_H + +/* /dev/zram-control interface */ +#define ZRAM_CTL_ADD 0x5C80 +#define ZRAM_CTL_REMOVE 0x5C81 + +#endif /* _UAPI_LINUX_ZRAM_H */ -- 2.3.1.167.g7f4ba4b -- 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/