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Message-ID: <b040c32a0705211940xe7cdf1cnb2c882edacc17a27@mail.gmail.com>
Date: Mon, 21 May 2007 19:40:14 -0700
From: "Ken Chen" <kenchen@...gle.com>
To: "Al Viro" <viro@....linux.org.uk>
Cc: akpm@...ux-foundation.org, mm-commits@...r.kernel.org,
viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org
Subject: Re: + loop-preallocate-eight-loop-devices.patch added to -mm tree
On 5/21/07, Ken Chen <kenchen@...gle.com> wrote:
> On 5/21/07, Al Viro <viro@....linux.org.uk> wrote:
> > No, it doesn't. Really. It's easy to split; untested incremental to your
> > patch follows:
> >
> > for (i = 0; i < nr; i++) {
> > - if (!loop_init_one(i))
> > - goto err;
> > + lo = loop_alloc(i);
> > + if (!lo)
> > + goto Enomem;
> > + list_add_tail(&lo->lo_list, &loop_devices);
> > }
>
> ah, yes, use the loop_device list_head to link all the pending devices.
>
>
> > + /* point of no return */
> > +
> > + list_for_each_entry(lo, &loop_devices, lo_list)
> > + add_disk(lo->lo_disk);
> > +
> > + blk_register_region(MKDEV(LOOP_MAJOR, 0), range,
> > + THIS_MODULE, loop_probe, NULL, NULL);
> > +
> > printk(KERN_INFO "loop: module loaded\n");
> > return 0;
> > -err:
> > - loop_exit();
> > +
> > +Enomem:
> > printk(KERN_INFO "loop: out of memory\n");
> > +
> > + while(!list_empty(&loop_devices)) {
> > + lo = list_entry(loop_devices.next, struct loop_device, lo_list);
> > + loop_del_one(lo);
> > + }
> > +
> > + unregister_blkdev(LOOP_MAJOR, "loop");
> > return -ENOMEM;
> > }
>
> I suppose the loop_del_one call in Enomem label needs to be split up
> too since in the error path, it hasn't done add_disk() yet?
tested, like this?
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 5526ead..0ed5470 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1354,7 +1354,7 @@ #endif
*/
static int max_loop;
module_param(max_loop, int, 0);
-MODULE_PARM_DESC(max_loop, "obsolete, loop device is created on-demand");
+MODULE_PARM_DESC(max_loop, "Maximum number of loop devices");
MODULE_LICENSE("GPL");
MODULE_ALIAS_BLOCKDEV_MAJOR(LOOP_MAJOR);
@@ -1394,16 +1394,11 @@ int loop_unregister_transfer
EXPORT_SYMBOL(loop_register_transfer);
EXPORT_SYMBOL(loop_unregister_transfer);
-static struct loop_device *loop_init_one(int i)
+static struct loop_device *loop_alloc(int i)
{
struct loop_device *lo;
struct gendisk *disk;
- list_for_each_entry(lo, &loop_devices, lo_list) {
- if (lo->lo_number == i)
- return lo;
- }
-
lo = kzalloc(sizeof(*lo), GFP_KERNEL);
if (!lo)
goto out;
@@ -1427,8 +1422,6 @@ static struct loop_device *loop_init_one
disk->private_data = lo;
disk->queue = lo->lo_queue;
sprintf(disk->disk_name, "loop%d", i);
- add_disk(disk);
- list_add_tail(&lo->lo_list, &loop_devices);
return lo;
out_free_queue:
@@ -1439,15 +1432,37 @@ out:
return NULL;
}
-static void loop_del_one(struct loop_device *lo)
+static void loop_free(struct loop_device *lo)
{
- del_gendisk(lo->lo_disk);
blk_cleanup_queue(lo->lo_queue);
put_disk(lo->lo_disk);
list_del(&lo->lo_list);
kfree(lo);
}
+static struct loop_device *loop_init_one(int i)
+{
+ struct loop_device *lo;
+
+ list_for_each_entry(lo, &loop_devices, lo_list) {
+ if (lo->lo_number == i)
+ return lo;
+ }
+
+ lo = loop_alloc(i);
+ if (lo) {
+ add_disk(lo->lo_disk);
+ list_add_tail(&lo->lo_list, &loop_devices);
+ }
+ return lo;
+}
+
+static void loop_del_one(struct loop_device *lo)
+{
+ del_gendisk(lo->lo_disk);
+ loop_free(lo);
+}
+
static struct kobject *loop_probe(dev_t dev, int *part, void *data)
{
struct loop_device *lo;
@@ -1464,28 +1479,77 @@ static struct kobject *loop_probe
static int __init loop_init(void)
{
- if (register_blkdev(LOOP_MAJOR, "loop"))
- return -EIO;
- blk_register_region(MKDEV(LOOP_MAJOR, 0), 1UL << MINORBITS,
- THIS_MODULE, loop_probe, NULL, NULL);
+ int i, nr;
+ unsigned long range;
+ struct loop_device *lo, *next;
+
+ /*
+ * 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.
+ */
+ if (max_loop > 1UL << MINORBITS)
+ return -EINVAL;
if (max_loop) {
- printk(KERN_INFO "loop: the max_loop option is obsolete "
- "and will be removed in March 2008\n");
+ nr = max_loop;
+ range = max_loop;
+ } else {
+ nr = 8;
+ range = 1UL << MINORBITS;
+ }
+
+ if (register_blkdev(LOOP_MAJOR, "loop"))
+ return -EIO;
+ for (i = 0; i < nr; i++) {
+ lo = loop_alloc(i);
+ if (!lo)
+ goto Enomem;
+ list_add_tail(&lo->lo_list, &loop_devices);
}
+
+ /* point of no return */
+
+ list_for_each_entry(lo, &loop_devices, lo_list)
+ add_disk(lo->lo_disk);
+
+ blk_register_region(MKDEV(LOOP_MAJOR, 0), range,
+ THIS_MODULE, loop_probe, NULL, NULL);
+
printk(KERN_INFO "loop: module loaded\n");
return 0;
+
+Enomem:
+ printk(KERN_INFO "loop: out of memory\n");
+
+ list_for_each_entry_safe(lo, next, &loop_devices, lo_list)
+ loop_free(lo);
+
+ unregister_blkdev(LOOP_MAJOR, "loop");
+ return -ENOMEM;
}
static void __exit loop_exit(void)
{
+ unsigned long range;
struct loop_device *lo, *next;
+ range = max_loop ? max_loop : 1UL << MINORBITS;
+
list_for_each_entry_safe(lo, next, &loop_devices, lo_list)
loop_del_one(lo);
- blk_unregister_region(MKDEV(LOOP_MAJOR, 0), 1UL << MINORBITS);
+ blk_unregister_region(MKDEV(LOOP_MAJOR, 0), range);
if (unregister_blkdev(LOOP_MAJOR, "loop"))
printk(KERN_WARNING "loop: cannot unregister blkdev\n");
}
-
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