From: "Ken Chen" Remove artificial maximum 256 loop device that can be created due to a legacy device number limit. Searching through lkml archive, there are several instances where users complained about the artificial limit that the loop driver impose. There is no reason to have such limit. This patch rid the limit entirely and make loop device and associated block queue instantiation on demand. With on-demand instantiation, it also gives the benefit of not wasting memory if these devices are not in use (compare to current implementation that always create 8 loop devices), a net improvement in both areas. This version is both tested with creation of large number of loop devices and is compatible with existing losetup/mount user land tools. There are a number of people who worked on this and provided valuable suggestions, in no particular order, by: Jens Axboe Jan Engelhardt Christoph Hellwig Thomas M Signed-off-by: Ken Chen Cc: Jan Engelhardt Cc: Christoph Hellwig Signed-off-by: Andrew Morton --- drivers/block/loop.c | 190 ++++++++++++++++++++++++----------------- include/linux/loop.h | 2 2 files changed, 115 insertions(+), 77 deletions(-) diff -puN drivers/block/loop.c~remove-artificial-software-max_loop-limit drivers/block/loop.c --- a/drivers/block/loop.c~remove-artificial-software-max_loop-limit +++ a/drivers/block/loop.c @@ -77,9 +77,8 @@ #include -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_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); 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); - 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 } #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, 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 /* * 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) { - 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; + + 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) +{ + 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 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)); - - disks = kmalloc(max_loop * sizeof(struct gendisk *), GFP_KERNEL); - if (!disks) - goto out_mem2; - - 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); + lo = loop_init_one(0); + if (IS_ERR(lo)) + goto out; + + if (max_loop) { + printk(KERN_INFO "loop: the max_loop option is obsolete " + "and will be removed in March 2008\n"); + + } + 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 -puN include/linux/loop.h~remove-artificial-software-max_loop-limit include/linux/loop.h --- a/include/linux/loop.h~remove-artificial-software-max_loop-limit +++ a/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__ */ _