loop: replace linked list of allocated devices with an idr index

Replace the linked list, that keeps track of allocated devices, with an
idr index to allow a more efficient lookup of devices.

Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 76c8da78212bffec71f5dc7af025a84e4028d456..f58532e777773e41f20285d1cf1787e304c8ee5e 100644 (file)
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -78,8 +78,8 @@
 
 #include <asm/uaccess.h>
 
-static LIST_HEAD(loop_devices);
-static DEFINE_MUTEX(loop_devices_mutex);
+static DEFINE_IDR(loop_index_idr);
+static DEFINE_MUTEX(loop_index_mutex);
 
 static int max_part;
 static int part_shift;
@@ -722,17 +722,10 @@ static inline int is_loop_device(struct file *file)
 static ssize_t loop_attr_show(struct device *dev, char *page,
                              ssize_t (*callback)(struct loop_device *, char *))
 {
-       struct loop_device *l, *lo = NULL;
-
-       mutex_lock(&loop_devices_mutex);
-       list_for_each_entry(l, &loop_devices, lo_list)
-               if (disk_to_dev(l->lo_disk) == dev) {
-                       lo = l;
-                       break;
-               }
-       mutex_unlock(&loop_devices_mutex);
+       struct gendisk *disk = dev_to_disk(dev);
+       struct loop_device *lo = disk->private_data;
 
-       return lo ? callback(lo, page) : -EIO;
+       return callback(lo, page);
 }
 
 #define LOOP_ATTR_RO(_name)                                            \
@@ -1557,40 +1550,64 @@ int loop_register_transfer(struct loop_func_table *funcs)
        return 0;
 }
 
+static int unregister_transfer_cb(int id, void *ptr, void *data)
+{
+       struct loop_device *lo = ptr;
+       struct loop_func_table *xfer = data;
+
+       mutex_lock(&lo->lo_ctl_mutex);
+       if (lo->lo_encryption == xfer)
+               loop_release_xfer(lo);
+       mutex_unlock(&lo->lo_ctl_mutex);
+       return 0;
+}
+
 int loop_unregister_transfer(int number)
 {
        unsigned int n = number;
-       struct loop_device *lo;
        struct loop_func_table *xfer;
 
        if (n == 0 || n >= MAX_LO_CRYPT || (xfer = xfer_funcs[n]) == NULL)
                return -EINVAL;
 
        xfer_funcs[n] = NULL;
-
-       list_for_each_entry(lo, &loop_devices, lo_list) {
-               mutex_lock(&lo->lo_ctl_mutex);
-
-               if (lo->lo_encryption == xfer)
-                       loop_release_xfer(lo);
-
-               mutex_unlock(&lo->lo_ctl_mutex);
-       }
-
+       idr_for_each(&loop_index_idr, &unregister_transfer_cb, xfer);
        return 0;
 }
 
 EXPORT_SYMBOL(loop_register_transfer);
 EXPORT_SYMBOL(loop_unregister_transfer);
 
-static struct loop_device *loop_alloc(int i)
+static int loop_add(struct loop_device **l, int i)
 {
        struct loop_device *lo;
        struct gendisk *disk;
+       int err;
 
        lo = kzalloc(sizeof(*lo), GFP_KERNEL);
-       if (!lo)
+       if (!lo) {
+               err = -ENOMEM;
                goto out;
+       }
+
+       err = idr_pre_get(&loop_index_idr, GFP_KERNEL);
+       if (err < 0)
+               goto out_free_dev;
+
+       if (i >= 0) {
+               int m;
+
+               /* create specific i in the index */
+               err = idr_get_new_above(&loop_index_idr, lo, i, &m);
+               if (err >= 0 && i != m) {
+                       idr_remove(&loop_index_idr, m);
+                       err = -EEXIST;
+               }
+       } else {
+               err = -EINVAL;
+       }
+       if (err < 0)
+               goto out_free_dev;
 
        lo->lo_queue = blk_alloc_queue(GFP_KERNEL);
        if (!lo->lo_queue)
@@ -1611,56 +1628,54 @@ static struct loop_device *loop_alloc(int i)
        disk->private_data      = lo;
        disk->queue             = lo->lo_queue;
        sprintf(disk->disk_name, "loop%d", i);
-       return lo;
+       add_disk(disk);
+       *l = lo;
+       return lo->lo_number;
 
 out_free_queue:
        blk_cleanup_queue(lo->lo_queue);
 out_free_dev:
        kfree(lo);
 out:
-       return NULL;
+       return err;
 }
 
-static void loop_free(struct loop_device *lo)
+static void loop_remove(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)
+static int loop_lookup(struct loop_device **l, int i)
 {
        struct loop_device *lo;
+       int ret = -ENODEV;
 
-       list_for_each_entry(lo, &loop_devices, lo_list) {
-               if (lo->lo_number == i)
-                       return lo;
-       }
-
-       lo = loop_alloc(i);
+       lo = idr_find(&loop_index_idr, i);
        if (lo) {
-               add_disk(lo->lo_disk);
-               list_add_tail(&lo->lo_list, &loop_devices);
+               *l = lo;
+               ret = lo->lo_number;
        }
-       return lo;
-}
-
-static void loop_del_one(struct loop_device *lo)
-{
-       del_gendisk(lo->lo_disk);
-       loop_free(lo);
+       return ret;
 }
 
 static struct kobject *loop_probe(dev_t dev, int *part, void *data)
 {
        struct loop_device *lo;
        struct kobject *kobj;
+       int err;
 
-       mutex_lock(&loop_devices_mutex);
-       lo = loop_init_one(MINOR(dev) >> part_shift);
-       kobj = lo ? get_disk(lo->lo_disk) : ERR_PTR(-ENOMEM);
-       mutex_unlock(&loop_devices_mutex);
+       mutex_lock(&loop_index_mutex);
+       err = loop_lookup(&lo, MINOR(dev) >> part_shift);
+       if (err < 0)
+               err = loop_add(&lo, MINOR(dev) >> part_shift);
+       if (err < 0)
+               kobj = ERR_PTR(err);
+       else
+               kobj = get_disk(lo->lo_disk);
+       mutex_unlock(&loop_index_mutex);
 
        *part = 0;
        return kobj;
@@ -1670,7 +1685,7 @@ static int __init loop_init(void)
 {
        int i, nr;
        unsigned long range;
-       struct loop_device *lo, *next;
+       struct loop_device *lo;
 
        /*
         * loop module now has a feature to instantiate underlying device
@@ -1719,43 +1734,36 @@ static int __init loop_init(void)
        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);
 
+       /* pre-create number devices of devices given by config or max_loop */
+       mutex_lock(&loop_index_mutex);
+       for (i = 0; i < nr; i++)
+               loop_add(&lo, i);
+       mutex_unlock(&loop_index_mutex);
+
        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);
+static int loop_exit_cb(int id, void *ptr, void *data)
+{
+       struct loop_device *lo = ptr;
 
-       unregister_blkdev(LOOP_MAJOR, "loop");
-       return -ENOMEM;
+       loop_remove(lo);
+       return 0;
 }
 
 static void __exit loop_exit(void)
 {
        unsigned long range;
-       struct loop_device *lo, *next;
 
        range = max_loop ? max_loop << part_shift : 1UL << MINORBITS;
 
-       list_for_each_entry_safe(lo, next, &loop_devices, lo_list)
-               loop_del_one(lo);
+       idr_for_each(&loop_index_idr, &loop_exit_cb, NULL);
+       idr_remove_all(&loop_index_idr);
+       idr_destroy(&loop_index_idr);
 
        blk_unregister_region(MKDEV(LOOP_MAJOR, 0), range);
        unregister_blkdev(LOOP_MAJOR, "loop");

diff --git a/include/linux/loop.h b/include/linux/loop.h
index 66c194e2d9b9c072fc201b864506ae12c010112d..5f08d18fa1480e19157fad9cd43b885055f6f494 100644 (file)
--- a/include/linux/loop.h
+++ b/include/linux/loop.h
@@ -64,7 +64,6 @@ struct loop_device {
 
        struct request_queue    *lo_queue;
        struct gendisk          *lo_disk;
-       struct list_head        lo_list;
 };
 
 #endif /* __KERNEL__ */