Messages in this thread |  | | | Date | Tue, 18 Mar 2008 13:54:23 -0700 | | From | Andrew Morton <> | | Subject | Re: [PATCH][RESEND][v3] Modify loop device to be able to manage partitions of the disk image |
| |
On Tue, 18 Mar 2008 13:19:20 +0100 Laurent Vivier <Laurent.Vivier@bull.net> wrote:
> v3 is an updated version of v2, replacing a "%d" by a "%lu". > > 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 "loop_max_part". > > For instance, to manage 63 partitions / loop device, we will do: > # modprobe loop 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 > EXT3 FS on loop0p1, internal journal > EXT3-fs: mounted filesystem with ordered data mode. > loop: module loaded > loop0: p1 p2 < p5 > > # 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 > kjournald starting. Commit interval 5 seconds > EXT3 FS on loop0p1, internal journal > EXT3-fs: mounted filesystem with ordered data mode. > # 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). > > ... > > index 9a5b665..7f2fd52 100644 > --- a/Documentation/kernel-parameters.txt > +++ b/Documentation/kernel-parameters.txt > @@ -1075,6 +1075,10 @@ and is between 256 and 4096 characters. It is defined in the file > be mounted > Format: <1-256> > > + loop_max_part= [LOOP] Maximum number of partitions per loopback device. > + Should be greater than 0, the maximum value depends > + on max_loop. > +
This shouldn't be needed.
> @@ -1360,6 +1367,8 @@ 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(loop_max_part, int, 0); > +MODULE_PARM_DESC(loop_max_part, "Maximum number of partitions per loop device");
Because this module_param() gives us the loop.loop_max_part=N kernel boot parameter.
Given which, I think we could rename it to just "max_part":
modprobe loop max_part=4
kernel vmlinuz-... loop.max_part=4
?
> __setup("max_loop=", max_loop_setup);
That could go away in the same way, but we have a back-compat problem.
> + > +static int __init max_part_setup(char *str) > +{ > + loop_max_part = simple_strtol(str, NULL, 0); > + if (loop_max_part > (1UL << (MINORBITS - 1))) { > + /* we must keep at least one bit for loop device number */ > + printk(KERN_ERR > + "loop: loop_max_part cannot be greater than %lu\n", > + 1UL << (MINORBITS - 1)); > + return 0; > + } > + return 1; > +} > + > +__setup("loop_max_part=", max_part_setup);
|  |