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Date: Thu, 06 Mar 2008 11:16:25 +0100 From: Laurent Vivier <Laurent.Vivier@...l.net> To: Nick Piggin <nickpiggin@...oo.com.au> Cc: linux-kernel@...r.kernel.org Subject: Re: [PATCH] Modify loop device to be able to manage partitions of the disk image Le jeudi 06 mars 2008 à 20:57 +1100, Nick Piggin a écrit : > On Thursday 06 March 2008 20:43, 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". > > > > For instance, to manage 63 partitions / loop device, we will do: > > # modprobe 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). Moreover all partition tables known > > by the kernel are managed (kpartx implements only a subset). > > Do you think we do something similar for drivers/block/brd.c too? I'd > like to try to maintain parity between them where possible... I think it is possible (I've the same patch for NBD too), but I think it is completely useless. For loop, it is another story because it uses disk images that can be created from a partition or a real device (or a virtual disk). Regards, Laurent -- ----------------- Laurent.Vivier@...l.net ------------------ "Programmers who subconsciously view themselves as artists will enjoy what they do and will do it better." D. Knuth -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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