Messages in this thread | | | Date | Wed, 19 Mar 2008 13:11:06 -0700 | From | Randy Dunlap <> | Subject | Re: [PATCH][v4] Modify loop device to be able to manage partitions of the disk image |
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On Wed, 19 Mar 2008 13:36:07 +0100 Laurent Vivier wrote:
> 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".
What happened to the update to Documentation/kernel-parameters.txt that was in v3?
> 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> > --- > drivers/block/loop.c | 26 +++++++++++++++++++++----- > 1 files changed, 21 insertions(+), 5 deletions(-) > > diff --git a/drivers/block/loop.c b/drivers/block/loop.c > index 91ebb00..f7f1635 100644 > --- a/drivers/block/loop.c > +++ b/drivers/block/loop.c > @@ -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); > --
--- ~Randy
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