2 files changed, 112 insertions, 74 deletions

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 0d4ccd4a0957..af6d7274a7cc 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -77,9 +77,8 @@
 
 #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_MUTEX(loop_devices_mutex);
 
 /*
  * 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_device *lo, struct file *lo_file,
         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);
         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_device *lo, struct block_device *bdev)
         memset(lo->lo_crypt_name, 0, LO_NAME_SIZE);
         memset(lo->lo_file_name, 0, LO_NAME_SIZE);
         invalidate_bdev(bdev);
-        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 +1321,18 @@ static long lo_compat_ioctl(struct file *file, unsigned int cmd, unsigned long a
 }
 #endif
 
+static struct loop_device *loop_find_dev(int number)
+{
+        struct loop_device *lo;
+
+        list_for_each_entry(lo, &loop_devices, lo_list) {
+                if (lo->lo_number == number)
+                        return lo;
+        }
+        return 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 +1341,11 @@ static int lo_open(struct inode *inode, struct file *file)
         lo->lo_refcnt++;
         mutex_unlock(&lo->lo_ctl_mutex);
 
+        mutex_lock(&loop_devices_mutex);
+        if (!loop_find_dev(lo->lo_number + 1))
+                loop_init_one(lo->lo_number + 1);
+        mutex_unlock(&loop_devices_mutex);
+
         return 0;
 }
 
@@ -1357,8 +1373,9 @@ static struct block_device_operations lo_fops = {
 /*
  * And now the modules code and kernel interface.
  */
+static int max_loop;
 module_param(max_loop, int, 0);
-MODULE_PARM_DESC(max_loop, "Maximum number of loop devices (1-256)");
+MODULE_PARM_DESC(max_loop, "obsolete, loop device is created on-demand");
 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)
@@ -1398,91 +1415,110 @@ 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)
+{
+        struct loop_device *lo;
+        struct gendisk *disk;
+
+        lo = kzalloc(sizeof(*lo), GFP_KERNEL);
+        if (!lo)
+                goto out;
+
+        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);
+        list_add_tail(&lo->lo_list, &loop_devices);
+        return lo;
+
+out_free_queue:
+        blk_cleanup_queue(lo->lo_queue);
+out_free_dev:
+        kfree(lo);
+out:
+        return ERR_PTR(-ENOMEM);
+}
+
+static void loop_del_one(struct loop_device *lo)
 {
-        int     i;
+        del_gendisk(lo->lo_disk);
+        blk_cleanup_queue(lo->lo_queue);
+        put_disk(lo->lo_disk);
+        list_del(&lo->lo_list);
+        kfree(lo);
+}
 
-        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;
-        }
+static struct kobject *loop_probe(dev_t dev, int *part, void *data)
+{
+        unsigned int number = dev & MINORMASK;
+        struct loop_device *lo;
+
+        mutex_lock(&loop_devices_mutex);
+        lo = loop_find_dev(number);
+        if (lo == NULL)
+                lo = loop_init_one(number);
+        mutex_unlock(&loop_devices_mutex);
+
+        *part = 0;
+        if (IS_ERR(lo))
+                return (void *)lo;
+        else
+                return &lo->lo_disk->kobj;
+}
+
+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);
 
-        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));
+        lo = loop_init_one(0);
+        if (IS_ERR(lo))
+                goto out;
 
-        disks = kmalloc(max_loop * sizeof(struct gendisk *), GFP_KERNEL);
-        if (!disks)
-                goto out_mem2;
+        if (max_loop) {
+                printk(KERN_INFO "loop: the max_loop option is obsolete "
+                                 "and will be removed in March 2008\n");
 
-        for (i = 0; i < max_loop; i++) {
-                disks[i] = alloc_disk(1);
-                if (!disks[i])
-                        goto out_mem3;
         }
-
-        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;
-        }
-
-        /* 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);
+        printk(KERN_INFO "loop: module loaded\n");
         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:
         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);
diff --git a/include/linux/loop.h b/include/linux/loop.h
index 191a595055f0..0b99b31f017b 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__ */