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loop: manage partitions in disk image

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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: Laurent Vivier <Laurent.Vivier@bull.net>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Laurent Vivier 2008-03-26 12:11:53 +01:00 committed by Jens Axboe
parent 22a9189fd0
commit 476a4813cf
1 changed files with 21 additions and 5 deletions
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26
drivers/block/loop.c
View File

@ -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);