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Date: Wed, 19 Mar 2008 21:24:41 +0100
From: Laurent Vivier <Laurent.Vivier@...l.net>
To: Randy Dunlap <randy.dunlap@...cle.com>
Cc: akpm@...ux-foundation.org, jens.axboe@...cle.com,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH][v4] Modify loop device to be able to manage
partitions of the disk image
Le mercredi 19 mars 2008 à 13:11 -0700, Randy Dunlap a écrit :
> 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?
Well, perhaps I didn't understand the comment of Andrew:
"This shouldn't be needed."
I though it means I should remove it. So, Andrew ???
And to comment the changes between v3 and v4:
- remove modification from kernel-parameters.txt (as you saw)
- rename the parameter to max_part (according Andrew comments)
- add an "ioctl_by_bdev(bdev, BLKRRPART, 0);" on loop_clr_fd()
(to remove loopXpY from /dev/ on "losetup -d")
Laurent
>
> > 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@...l.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
>
--
------- Laurent.Vivier@...l.net -------
"The best way to predict the future
is to invent it." - Alan Kay
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