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Date: Tue, 11 Mar 2008 10:38:47 +0100
From: Laurent Vivier <Laurent.Vivier@...l.net>
To: linux-kernel@...r.kernel.org
Cc: Laurent Vivier <Laurent.Vivier@...l.net>
Subject: [PATCH][v3] Modify loop device to be able to manage partitions of the disk image
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).
Signed-off-by: Laurent Vivier <Laurent.Vivier@...l.net>
---
Documentation/kernel-parameters.txt | 4 +++
drivers/block/loop.c | 39 ++++++++++++++++++++++++++++++----
2 files changed, 38 insertions(+), 5 deletions(-)
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
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.
+
maxcpus= [SMP] Maximum number of processors that an SMP kernel
should make use of. maxcpus=n : n >= 0 limits the
kernel to using 'n' processors. n=0 is a special case,
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 91ebb00..16b2aa6 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 loop_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 (loop_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 (loop_max_part > 0)
+ ioctl_by_bdev(bdev, BLKRRPART, 0);
return 0;
out_clr:
@@ -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");
MODULE_LICENSE("GPL");
MODULE_ALIAS_BLOCKDEV_MAJOR(LOOP_MAJOR);
@@ -1412,7 +1421,7 @@ 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 +1431,7 @@ 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 +1511,12 @@ 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 (loop_max_part > 0)
+ part_shift = fls(loop_max_part);
+
+ if (max_loop > 1UL << (MINORBITS - part_shift))
return -EINVAL;
if (max_loop) {
@@ -1510,7 +1524,7 @@ 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 +1563,7 @@ 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);
@@ -1569,4 +1583,19 @@ static int __init max_loop_setup(char *str)
}
__setup("max_loop=", max_loop_setup);
+
+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);
#endif
--
1.5.2.4
--
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