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>

1 files changed, 80 insertions, 72 deletions

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 76c8da78212b..f58532e77777 100644
--- 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");