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Commit 476a4813 authored by Laurent Vivier's avatar Laurent Vivier Committed by Jens Axboe
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loop: manage partitions in disk image 



This patch allows to use loop device with partitionned disk image.

Original behavior of loop is not modified.

A new parameter is introduced to define how many partition we want to be
able to manage per loop device. This parameter is "max_part".

For instance, to manage 63 partitions / loop device, we will do:
# modprobe loop max_part=63
# ls -l /dev/loop?*
brw-rw---- 1 root disk 7,   0 2008-03-05 14:55 /dev/loop0
brw-rw---- 1 root disk 7,  64 2008-03-05 14:55 /dev/loop1
brw-rw---- 1 root disk 7, 128 2008-03-05 14:55 /dev/loop2
brw-rw---- 1 root disk 7, 192 2008-03-05 14:55 /dev/loop3
brw-rw---- 1 root disk 7, 256 2008-03-05 14:55 /dev/loop4
brw-rw---- 1 root disk 7, 320 2008-03-05 14:55 /dev/loop5
brw-rw---- 1 root disk 7, 384 2008-03-05 14:55 /dev/loop6
brw-rw---- 1 root disk 7, 448 2008-03-05 14:55 /dev/loop7

And to attach a raw partitionned disk image, the original losetup is used:

# losetup -f etch.img
# ls -l /dev/loop?*
brw-rw---- 1 root disk 7,   0 2008-03-05 14:55 /dev/loop0
brw-rw---- 1 root disk 7,   1 2008-03-05 14:57 /dev/loop0p1
brw-rw---- 1 root disk 7,   2 2008-03-05 14:57 /dev/loop0p2
brw-rw---- 1 root disk 7,   5 2008-03-05 14:57 /dev/loop0p5
brw-rw---- 1 root disk 7,  64 2008-03-05 14:55 /dev/loop1
brw-rw---- 1 root disk 7, 128 2008-03-05 14:55 /dev/loop2
brw-rw---- 1 root disk 7, 192 2008-03-05 14:55 /dev/loop3
brw-rw---- 1 root disk 7, 256 2008-03-05 14:55 /dev/loop4
brw-rw---- 1 root disk 7, 320 2008-03-05 14:55 /dev/loop5
brw-rw---- 1 root disk 7, 384 2008-03-05 14:55 /dev/loop6
brw-rw---- 1 root disk 7, 448 2008-03-05 14:55 /dev/loop7
# mount /dev/loop0p1 /mnt
# ls /mnt
bench  cdrom  home        lib         mnt   root     srv  usr
bin    dev    initrd      lost+found  opt   sbin     sys  var
boot   etc    initrd.img  media       proc  selinux  tmp  vmlinuz
# umount /mnt
# losetup -d /dev/loop0

Of course, the same behavior can be done using kpartx on a loop device,
but modifying loop avoids to stack several layers of block device (loop +
device mapper), this is a very light modification (40% of modifications
are to manage the new parameter).

Signed-off-by: default avatarLaurent Vivier <Laurent.Vivier@bull.net>
Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent 22a9189f

drivers/block/loop.c

+21 −5
Original line number Diff line number Diff line
@@ -82,6 +82,9 @@ 
static LIST_HEAD(loop_devices);

static DEFINE_MUTEX(loop_devices_mutex);



static int max_part;

static int part_shift;



/*

 * Transfer functions

 */
@@ -692,6 +695,8 @@ static int loop_change_fd(struct loop_device *lo, struct file *lo_file, 
		goto out_putf;



	fput(old_file);

	if (max_part > 0)

		ioctl_by_bdev(bdev, BLKRRPART, 0);

	return 0;



 out_putf:
@@ -819,6 +824,8 @@ static int loop_set_fd(struct loop_device *lo, struct file *lo_file, 
	}

	lo->lo_state = Lo_bound;

	wake_up_process(lo->lo_thread);

	if (max_part > 0)

		ioctl_by_bdev(bdev, BLKRRPART, 0);

	return 0;



out_clr:
@@ -919,6 +926,8 @@ static int loop_clr_fd(struct loop_device *lo, struct block_device *bdev) 
	fput(filp);

	/* This is safe: open() is still holding a reference. */

	module_put(THIS_MODULE);

	if (max_part > 0)

		ioctl_by_bdev(bdev, BLKRRPART, 0);

	return 0;

}
@@ -1360,6 +1369,8 @@ static struct block_device_operations lo_fops = { 
static int max_loop;

module_param(max_loop, int, 0);

MODULE_PARM_DESC(max_loop, "Maximum number of loop devices");

module_param(max_part, int, 0);

MODULE_PARM_DESC(max_part, "Maximum number of partitions per loop device");

MODULE_LICENSE("GPL");

MODULE_ALIAS_BLOCKDEV_MAJOR(LOOP_MAJOR);
@@ -1412,7 +1423,7 @@ static struct loop_device *loop_alloc(int i) 
	if (!lo->lo_queue)

		goto out_free_dev;



	disk = lo->lo_disk = alloc_disk(1);

	disk = lo->lo_disk = alloc_disk(1 << part_shift);

	if (!disk)

		goto out_free_queue;
@@ -1422,7 +1433,7 @@ static struct loop_device *loop_alloc(int i) 
	init_waitqueue_head(&lo->lo_event);

	spin_lock_init(&lo->lo_lock);

	disk->major		= LOOP_MAJOR;

	disk->first_minor	= i;

	disk->first_minor	= i << part_shift;

	disk->fops		= &lo_fops;

	disk->private_data	= lo;

	disk->queue		= lo->lo_queue;
@@ -1502,7 +1513,12 @@ static int __init loop_init(void) 
	 *     themselves and have kernel automatically instantiate actual

	 *     device on-demand.

	 */

	if (max_loop > 1UL << MINORBITS)



	part_shift = 0;

	if (max_part > 0)

		part_shift = fls(max_part);



	if (max_loop > 1UL << (MINORBITS - part_shift))

		return -EINVAL;



	if (max_loop) {
@@ -1510,7 +1526,7 @@ static int __init loop_init(void) 
		range = max_loop;

	} else {

		nr = 8;

		range = 1UL << MINORBITS;

		range = 1UL << (MINORBITS - part_shift);

	}



	if (register_blkdev(LOOP_MAJOR, "loop"))
@@ -1549,7 +1565,7 @@ static void __exit loop_exit(void) 
	unsigned long range;

	struct loop_device *lo, *next;



	range = max_loop ? max_loop :  1UL << MINORBITS;

	range = max_loop ? max_loop :  1UL << (MINORBITS - part_shift);



	list_for_each_entry_safe(lo, next, &loop_devices, lo_list)

		loop_del_one(lo);