Re: [PATCH] max_loop limit, loop.c final working version

Tomas M
2007-03-29T08:38:55Z

[-- Attachment #1: Type: text/plain, Size: 714 bytes --]

This is a diff from Ken Chen, who sent it to me a week ago and received
the claimed prize $256. I think it's partially based on Jan's code,
while if fixes the bug Jan mentioned (as far as I know).

It does the following:
- allocate loop dynamically on the fly
- allocate one more (spare) loop each time,
so losetup and mount tools can work correctly
- doesn't need any module parameters

Unfortunately 'mount' and 'losetup' binaries are hardcoded to stop
searching for free loop device after the minor num 255, so one have to
use a workaround in order to use more loops with 'mount':

$ losetup /dev/loop1000 file
$ mount /dev/loop1000 /mntpnt

I hope these binaries will be fixed soon.

Tomas M
slax.org

[-- Attachment #2: loop.c.diff --]
[-- Type: text/x-patch, Size: 7610 bytes --]

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 6b5b642..7db2c38 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -77,9 +77,8 @@ #include <linux/kthread.h>

#include <asm/uaccess.h>

-static int max_loop = 8;
-static struct loop_device *loop_dev;
-static struct gendisk **disks;
+static LIST_HEAD(loop_devices);
+static DEFINE_SPINLOCK(loop_devices_lock);

/*
* Transfer functions
@@ -183,7 +182,7 @@ figure_loop_size(struct loop_device *lo)
if (unlikely((loff_t)x != size))
return -EFBIG;

- set_capacity(disks[lo->lo_number], x);
+ set_capacity(lo->lo_disk, x);
return 0;
}

@@ -812,7 +811,7 @@ static int loop_set_fd(struct loop_devic
lo->lo_queue->queuedata = lo;
lo->lo_queue->unplug_fn = loop_unplug;

- set_capacity(disks[lo->lo_number], size);
+ set_capacity(lo->lo_disk, size);
bd_set_size(bdev, size << 9);

set_blocksize(bdev, lo_blocksize);
@@ -832,7 +831,7 @@ out_clr:
lo->lo_device = NULL;
lo->lo_backing_file = NULL;
lo->lo_flags = 0;
- set_capacity(disks[lo->lo_number], 0);
+ set_capacity(lo->lo_disk, 0);
invalidate_bdev(bdev, 0);
bd_set_size(bdev, 0);
mapping_set_gfp_mask(mapping, lo->old_gfp_mask);
@@ -918,7 +917,7 @@ static int loop_clr_fd(struct loop_devic
memset(lo->lo_crypt_name, 0, LO_NAME_SIZE);
memset(lo->lo_file_name, 0, LO_NAME_SIZE);
invalidate_bdev(bdev, 0);
- set_capacity(disks[lo->lo_number], 0);
+ set_capacity(lo->lo_disk, 0);
bd_set_size(bdev, 0);
mapping_set_gfp_mask(filp->f_mapping, gfp);
lo->lo_state = Lo_unbound;
@@ -1322,6 +1321,23 @@ static long lo_compat_ioctl(struct file
}
#endif

+static struct loop_device *loop_find_dev(int number)
+{
+ struct loop_device *lo;
+ int found = 0;
+
+ spin_lock(&loop_devices_lock);
+ list_for_each_entry(lo, &loop_devices, lo_list) {
+ if (lo->lo_number == number) {
+ found = 1;
+ break;
+ }
+ }
+ spin_unlock(&loop_devices_lock);
+ return found ? lo : NULL;
+}
+
+static struct loop_device *loop_init_one(int i);
static int lo_open(struct inode *inode, struct file *file)
{
struct loop_device *lo = inode->i_bdev->bd_disk->private_data;
@@ -1330,6 +1346,9 @@ static int lo_open(struct inode *inode,
lo->lo_refcnt++;
mutex_unlock(&lo->lo_ctl_mutex);

+ if (!loop_find_dev(lo->lo_number + 1))
+ loop_init_one(lo->lo_number + 1);
+
return 0;
}

@@ -1357,8 +1376,6 @@ #endif
/*
* And now the modules code and kernel interface.
*/
-module_param(max_loop, int, 0);
-MODULE_PARM_DESC(max_loop, "Maximum number of loop devices (1-256)");
MODULE_LICENSE("GPL");
MODULE_ALIAS_BLOCKDEV_MAJOR(LOOP_MAJOR);

@@ -1383,7 +1400,7 @@ int loop_unregister_transfer(int number)

xfer_funcs[n] = NULL;

- for (lo = &loop_dev[0]; lo < &loop_dev[max_loop]; lo++) {
+ list_for_each_entry(lo, &loop_devices, lo_list) {
mutex_lock(&lo->lo_ctl_mutex);

if (lo->lo_encryption == xfer)
@@ -1398,102 +1415,104 @@ int loop_unregister_transfer(int number)
EXPORT_SYMBOL(loop_register_transfer);
EXPORT_SYMBOL(loop_unregister_transfer);

-static int __init loop_init(void)
+static struct loop_device *loop_init_one(int i)
{
- int i;
+ struct loop_device *lo;
+ struct gendisk *disk;

- if (max_loop < 1 || max_loop > 256) {
- printk(KERN_WARNING "loop: invalid max_loop (must be between"
- " 1 and 256), using default (8)\n");
- max_loop = 8;
- }
+ lo = kzalloc(sizeof(*lo), GFP_KERNEL);
+ if (!lo)
+ goto out;

- if (register_blkdev(LOOP_MAJOR, "loop"))
- return -EIO;
+ lo->lo_queue = blk_alloc_queue(GFP_KERNEL);
+ if (!lo->lo_queue)
+ goto out_free_dev;
+
+ disk = lo->lo_disk = alloc_disk(1);
+ if (!disk)
+ goto out_free_queue;
+
+ mutex_init(&lo->lo_ctl_mutex);
+ lo->lo_number = i;
+ lo->lo_thread = NULL;
+ init_waitqueue_head(&lo->lo_event);
+ spin_lock_init(&lo->lo_lock);
+ disk->major = LOOP_MAJOR;
+ disk->first_minor = i;
+ disk->fops = &lo_fops;
+ disk->private_data = lo;
+ disk->queue = lo->lo_queue;
+ sprintf(disk->disk_name, "loop%d", i);
+ add_disk(disk);
+ spin_lock(&loop_devices_lock);
+ list_add_tail(&lo->lo_list, &loop_devices);
+ spin_unlock(&loop_devices_lock);
+ return lo;
+
+out_free_queue:
+ blk_cleanup_queue(lo->lo_queue);
+out_free_dev:
+ kfree(lo);
+out:
+ return ERR_PTR(-ENOMEM);
+}

- loop_dev = kmalloc(max_loop * sizeof(struct loop_device), GFP_KERNEL);
- if (!loop_dev)
- goto out_mem1;
- memset(loop_dev, 0, max_loop * sizeof(struct loop_device));
+static void loop_del_one(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);
+}

- disks = kmalloc(max_loop * sizeof(struct gendisk *), GFP_KERNEL);
- if (!disks)
- goto out_mem2;
+static struct kobject *loop_probe(dev_t dev, int *part, void *data)
+{
+ unsigned int number = dev & MINORMASK;
+ struct loop_device *lo;

- for (i = 0; i < max_loop; i++) {
- disks[i] = alloc_disk(1);
- if (!disks[i])
- goto out_mem3;
+ if ((lo = loop_find_dev(number)) == NULL) {
+ lo = loop_init_one(number);
+ *part = 0;
+ if (IS_ERR(lo))
+ return (void *)lo;
}
+ return &lo->lo_disk->kobj;
+}

- for (i = 0; i < max_loop; i++) {
- struct loop_device *lo = &loop_dev[i];
- struct gendisk *disk = disks[i];
-
- memset(lo, 0, sizeof(*lo));
- lo->lo_queue = blk_alloc_queue(GFP_KERNEL);
- if (!lo->lo_queue)
- goto out_mem4;
- mutex_init(&lo->lo_ctl_mutex);
- lo->lo_number = i;
- lo->lo_thread = NULL;
- init_waitqueue_head(&lo->lo_event);
- spin_lock_init(&lo->lo_lock);
- disk->major = LOOP_MAJOR;
- disk->first_minor = i;
- disk->fops = &lo_fops;
- sprintf(disk->disk_name, "loop%d", i);
- disk->private_data = lo;
- disk->queue = lo->lo_queue;
- }
+static int __init loop_init(void)
+{
+ struct loop_device *lo;
+
+ if (register_blkdev(LOOP_MAJOR, "loop"))
+ return -EIO;
+ blk_register_region(MKDEV(LOOP_MAJOR, 0), 1UL << MINORBITS,
+ THIS_MODULE, loop_probe, NULL, NULL);

- /* We cannot fail after we call this, so another loop!*/
- for (i = 0; i < max_loop; i++)
- add_disk(disks[i]);
- printk(KERN_INFO "loop: loaded (max %d devices)\n", max_loop);
+ lo = loop_init_one(0);
+ if (IS_ERR(lo))
+ goto out_free;
+
+ printk(KERN_INFO "loop: loaded");
return 0;

-out_mem4:
- while (i--)
- blk_cleanup_queue(loop_dev[i].lo_queue);
- i = max_loop;
-out_mem3:
- while (i--)
- put_disk(disks[i]);
- kfree(disks);
-out_mem2:
- kfree(loop_dev);
-out_mem1:
+out_free:
unregister_blkdev(LOOP_MAJOR, "loop");
printk(KERN_ERR "loop: ran out of memory\n");
return -ENOMEM;
}

-static void loop_exit(void)
+static void __exit loop_exit(void)
{
- int i;
+ struct loop_device *lo, *next;

- for (i = 0; i < max_loop; i++) {
- del_gendisk(disks[i]);
- blk_cleanup_queue(loop_dev[i].lo_queue);
- put_disk(disks[i]);
- }
+ list_for_each_entry_safe(lo, next, &loop_devices, lo_list)
+ loop_del_one(lo);
+
+ blk_unregister_region(MKDEV(LOOP_MAJOR, 0), 1UL << MINORBITS);
if (unregister_blkdev(LOOP_MAJOR, "loop"))
printk(KERN_WARNING "loop: cannot unregister blkdev\n");
-
- kfree(disks);
- kfree(loop_dev);
}

module_init(loop_init);
module_exit(loop_exit);
-
-#ifndef MODULE
-static int __init max_loop_setup(char *str)
-{
- max_loop = simple_strtol(str, NULL, 0);
- return 1;
-}
-
-__setup("max_loop=", max_loop_setup);
-#endif
diff --git a/include/linux/loop.h b/include/linux/loop.h
index 191a595..0b99b31 100644
--- a/include/linux/loop.h
+++ b/include/linux/loop.h
@@ -64,6 +64,8 @@ struct loop_device {
wait_queue_head_t lo_event;

request_queue_t *lo_queue;
+ struct gendisk *lo_disk;
+ struct list_head lo_list;
};

#endif /* __KERNEL__ */