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loop: add BLK_DEV_LOOP_MIN_COUNT=%i to allow distros 0 pre-allocated loop devices 

Instead of unconditionally creating a fixed number of dead loop
devices which need to be investigated by storage handling services,
even when they are never used, we allow distros start with 0
loop devices and have losetup(8) and similar switch to the dynamic
/dev/loop-control interface instead of searching /dev/loop%i for free
devices.

Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
This commit is contained in:
Kay Sievers 2011-07-31 22:08:04 +02:00 committed by Jens Axboe
parent 770fe30a46
commit d134b00b9a
3 changed files with 31 additions and 20 deletions
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9
Documentation/kernel-parameters.txt
View File

@ -1340,9 +1340,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
it is equivalent to "nosmp", which also disables
the IO APIC.
max_loop= [LOOP] Maximum number of loopback devices that can
be mounted
Format: <1-256>
max_loop= [LOOP] The number of loop block devices that get
(loop.max_loop) unconditionally pre-created at init time. The default
number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
of statically allocating a predefined number, loop
devices can be requested on-demand with the
/dev/loop-control interface.
mcatest= [IA-64]

15
drivers/block/Kconfig
View File

@ -256,6 +256,21 @@ config BLK_DEV_LOOP
Most users will answer N here.
config BLK_DEV_LOOP_MIN_COUNT
int "Number of loop devices to pre-create at init time"
depends on BLK_DEV_LOOP
default 8
help
Static number of loop devices to be unconditionally pre-created
at init time.
This default value can be overwritten on the kernel command
line or with module-parameter loop.max_loop.
The historic default is 8. If a late 2011 version of losetup(8)
is used, it can be set to 0, since needed loop devices can be
dynamically allocated with the /dev/loop-control interface.
config BLK_DEV_CRYPTOLOOP
tristate "Cryptoloop Support"
select CRYPTO

27
drivers/block/loop.c
View File

@ -1793,21 +1793,6 @@ static int __init loop_init(void)
struct loop_device *lo;
int err;
/*
* loop module now has a feature to instantiate underlying device
* structure on-demand, provided that there is an access dev node.
* However, this will not work well with user space tool that doesn't
* know about such "feature". In order to not break any existing
* tool, we do the following:
*
* (1) if max_loop is specified, create that many upfront, and this
* also becomes a hard limit.
* (2) if max_loop is not specified, create 8 loop device on module
* load, user can further extend loop device by create dev node
* themselves and have kernel automatically instantiate actual
* device on-demand.
*/
err = misc_register(&loop_misc);
if (err < 0)
return err;
@ -1833,11 +1818,19 @@ static int __init loop_init(void)
if (max_loop > 1UL << (MINORBITS - part_shift))
return -EINVAL;
/*
* If max_loop is specified, create that many devices upfront.
* This also becomes a hard limit. If max_loop is not specified,
* create CONFIG_BLK_DEV_LOOP_MIN_COUNT loop devices at module
* init time. Loop devices can be requested on-demand with the
* /dev/loop-control interface, or be instantiated by accessing
* a 'dead' device node.
*/
if (max_loop) {
nr = max_loop;
range = max_loop << part_shift;
} else {
nr = 8;
nr = CONFIG_BLK_DEV_LOOP_MIN_COUNT;
range = 1UL << MINORBITS;
}
@ -1847,7 +1840,7 @@ static int __init loop_init(void)
blk_register_region(MKDEV(LOOP_MAJOR, 0), range,
THIS_MODULE, loop_probe, NULL, NULL);
/* pre-create number devices of devices given by config or max_loop */
/* pre-create number of devices given by config or max_loop */
mutex_lock(&loop_index_mutex);
for (i = 0; i < nr; i++)
loop_add(&lo, i);