loop: add management interface for on-demand device allocation
Subsystems (2)
PATCH 2/3 loop: add management interface for on-demand device allocation
From: Kay Sievers <[email protected]>
Subject: loop: add management interface for on-demand device allocation
Loop devices today have a fixed pre-allocated number of usually 8. The number can only be changed at module init time. To find a free device to use, /dev/loop%i needs to be scanned, and all devices need to be opened until a free one is possibly found.
This adds a new /dev/loop-control device node, that allows to dynamically find or allocate a free device, and to add and remove loop devices from the running system:
LOOP_CTL_ADD adds a specific device. Arg is the number
of the device. It returns the device i or a negative
error code.
LOOP_CTL_REMOVE removes a specific device, Arg is the number the device. It returns the device i or a negative error code.
LOOP_CTL_GET_FREE finds the next unbound device or allocates a new one. No arg is given. It returns the device i or a negative error code.
The loop kernel module gets automatically loaded when /dev/loop-control is accessed the first time. The alias specified in the module, instructs udev to create this 'dead' device node, even when the module is not loaded.
Example:
cfd = open("/dev/loop-control", O_RDWR);
# add a new specific loop device err = ioctl(cfd, LOOP_CTL_ADD, devnr);
# remove a specific loop device err = ioctl(cfd, LOOP_CTL_REMOVE, devnr);
# find or allocate a free loop device to use devnr = ioctl(cfd, LOOP_CTL_GET_FREE);
sprintf(loopname, "/dev/loop%i", devnr);
ffd = open("backing-file", O_RDWR);
lfd = open(loopname, O_RDWR);
err = ioctl(lfd, LOOP_SET_FD, ffd);
--- drivers/block/loop.c | 120 +++++++++++++++++++++++++++++++++++++++++++-- include/linux/loop.h | 4 + include/linux/miscdevice.h | 1 3 files changed, 121 insertions(+), 4 deletions(-)
drivers/block/loop.c +116 -4
@@ -75,7 +75,7 @@#include <linux/kthread.h> #include <linux/splice.h> #include <linux/sysfs.h> - +#include <linux/miscdevice.h> #include <asm/uaccess.h> static DEFINE_IDR (loop_index_idr);
@@ -1478,13 +1478,22 @@ static int lo_compat_ioctl(struct block_static int lo_open (struct block_device *bdev,fmode_t mode) { -struct loop_device *lo = bdev->bd_disk->private_data; +struct loop_device *lo; +int err =0 ; + +mutex_lock (&loop_index_mutex); + lo = bdev->bd_disk->private_data; +if (!lo) { + err = -ENXIO ; + goto out; + }mutex_lock (&lo->lo_ctl_mutex); lo->lo_refcnt++;mutex_unlock (&lo->lo_ctl_mutex); - -return 0 ; +out: +mutex_unlock (&loop_index_mutex); +return err; }static int lo_release (struct gendisk *disk,fmode_t mode)
@@ -1603,6 +1612,13 @@ static int loop_add(struct loop_device *idr_remove (&loop_index_idr, m); err = -EEXIST ; } + }else if (i ==-1 ) { +int m; + +/* get next free nr */ + err =idr_get_new (&loop_index_idr, lo, &m); +if (err >=0 ) + i = m; }else { err = -EINVAL ; }
@@ -1648,16 +1664,41 @@ static void loop_remove(struct loop_devikfree (lo); } +static int find_free_cb (int id,void *ptr,void *data) +{ +struct loop_device *lo = ptr; +struct loop_device **l = data; + +if (lo->lo_state == Lo_unbound) { + *l = lo; +return 1 ; + } +return 0 ; +} +static int loop_lookup (struct loop_device **l,int i) {struct loop_device *lo;int ret = -ENODEV ; +if (i <0 ) { +int err; + + err =idr_for_each (&loop_index_idr, &find_free_cb, &lo); +if (err ==1 ) { + *l = lo; + ret = lo->lo_number; + } + goto out; + } + +/* lookup and return a specific i */ lo =idr_find (&loop_index_idr, i);if (lo) { *l = lo; ret = lo->lo_number; } +out:return ret; }
@@ -1681,11 +1722,76 @@ static struct kobject *loop_probe(dev_treturn kobj; } +static long loop_control_ioctl (struct file *file,unsigned int cmd, +unsigned long parm) +{ +struct loop_device *lo; +int ret = -ENOSYS ; + +mutex_lock (&loop_index_mutex); +switch (cmd) { +case LOOP_CTL_ADD : + ret =loop_lookup (&lo, parm); +if (ret >=0 ) { + ret = -EEXIST ; +break ; + } + ret =loop_add (&lo, parm); +break ; +case LOOP_CTL_REMOVE : + ret =loop_lookup (&lo, parm); +if (ret <0 ) +break ; +mutex_lock (&lo->lo_ctl_mutex); +if (lo->lo_state != Lo_unbound) { + ret = -EBUSY ; +mutex_unlock (&lo->lo_ctl_mutex); +break ; + } +if (lo->lo_refcnt >0 ) { + ret = -EBUSY ; +mutex_unlock (&lo->lo_ctl_mutex); +break ; + } + lo->lo_disk->private_data =NULL ; +mutex_unlock (&lo->lo_ctl_mutex); +idr_remove (&loop_index_idr, lo->lo_number); +loop_remove (lo); +break ; +case LOOP_CTL_GET_FREE : + ret =loop_lookup (&lo,-1 ); +if (ret >=0 ) +break ; + ret =loop_add (&lo,-1 ); + } +mutex_unlock (&loop_index_mutex); + +return ret; +} + +static const struct file_operations loop_ctl_fops = { + .open = nonseekable_open, + .unlocked_ioctl = loop_control_ioctl, + .compat_ioctl = loop_control_ioctl, + .owner =THIS_MODULE , + .llseek = noop_llseek, +}; + +static struct miscdevice loop_misc = { + .minor =LOOP_CTRL_MINOR , + .name ="loop-control" , + .fops = &loop_ctl_fops, +}; + +MODULE_ALIAS_MISCDEV (LOOP_CTRL_MINOR ); +MODULE_ALIAS ("devname:loop-control" ); +static int __init loop_init (void ) {int i, nr;unsigned long range;struct loop_device *lo; +int err;/* * loop module now has a feature to instantiate underlying device
@@ -1702,6 +1808,10 @@ static int __init loop_init(void)* device on-demand. */ + err =misc_register (&loop_misc); +if (err <0 ) +return err; + part_shift =0 ;if (max_part >0 ) { part_shift =fls (max_part);
@@ -1767,6 +1877,8 @@ static void __exit loop_exit(void)blk_unregister_region (MKDEV (LOOP_MAJOR ,0 ), range);unregister_blkdev (LOOP_MAJOR ,"loop" ); + +misc_deregister (&loop_misc); }module_init (loop_init);
include/linux/loop.h +4 -0
@@ -160,4 +160,8 @@ int loop_unregister_transfer(int number)#define LOOP_CHANGE_FD 0x4C06#define LOOP_SET_CAPACITY 0x4C07 +/* /dev/loop-control interface */ +#define LOOP_CTL_ADD 0x4C80 +#define LOOP_CTL_REMOVE 0x4C81 +#define LOOP_CTL_GET_FREE 0x4C82#endif
include/linux/miscdevice.h +1 -0
@@ -40,6 +40,7 @@#define BTRFS_MINOR 234#define AUTOFS_MINOR 235#define MAPPER_CTRL_MINOR 236 +#define LOOP_CTRL_MINOR 237#define MISC_DYNAMIC_MINOR 255struct device ;