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770fe30a46
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);
Cc: Tejun Heo <tj@kernel.org>
Cc: Karel Zak <kzak@redhat.com>
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
66 lines
1.8 KiB
C
66 lines
1.8 KiB
C
#ifndef _LINUX_MISCDEVICE_H
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#define _LINUX_MISCDEVICE_H
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#include <linux/module.h>
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#include <linux/major.h>
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/*
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* These allocations are managed by device@lanana.org. If you use an
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* entry that is not in assigned your entry may well be moved and
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* reassigned, or set dynamic if a fixed value is not justified.
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*/
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#define PSMOUSE_MINOR 1
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#define MS_BUSMOUSE_MINOR 2
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#define ATIXL_BUSMOUSE_MINOR 3
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/*#define AMIGAMOUSE_MINOR 4 FIXME OBSOLETE */
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#define ATARIMOUSE_MINOR 5
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#define SUN_MOUSE_MINOR 6
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#define APOLLO_MOUSE_MINOR 7
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#define PC110PAD_MINOR 9
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/*#define ADB_MOUSE_MINOR 10 FIXME OBSOLETE */
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#define WATCHDOG_MINOR 130 /* Watchdog timer */
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#define TEMP_MINOR 131 /* Temperature Sensor */
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#define RTC_MINOR 135
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#define EFI_RTC_MINOR 136 /* EFI Time services */
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#define SUN_OPENPROM_MINOR 139
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#define DMAPI_MINOR 140 /* DMAPI */
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#define NVRAM_MINOR 144
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#define SGI_MMTIMER 153
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#define STORE_QUEUE_MINOR 155
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#define I2O_MINOR 166
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#define MICROCODE_MINOR 184
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#define TUN_MINOR 200
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#define MWAVE_MINOR 219 /* ACP/Mwave Modem */
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#define MPT_MINOR 220
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#define MPT2SAS_MINOR 221
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#define UINPUT_MINOR 223
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#define HPET_MINOR 228
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#define FUSE_MINOR 229
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#define KVM_MINOR 232
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#define BTRFS_MINOR 234
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#define AUTOFS_MINOR 235
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#define MAPPER_CTRL_MINOR 236
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#define LOOP_CTRL_MINOR 237
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#define MISC_DYNAMIC_MINOR 255
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struct device;
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struct miscdevice {
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int minor;
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const char *name;
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const struct file_operations *fops;
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struct list_head list;
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struct device *parent;
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struct device *this_device;
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const char *nodename;
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mode_t mode;
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};
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extern int misc_register(struct miscdevice * misc);
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extern int misc_deregister(struct miscdevice *misc);
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#define MODULE_ALIAS_MISCDEV(minor) \
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MODULE_ALIAS("char-major-" __stringify(MISC_MAJOR) \
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"-" __stringify(minor))
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#endif
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