block, bdi: an active gendisk always has a request_queue associated with it

bdev_get_queue() returns the request_queue associated with the
specified block_device.  blk_get_backing_dev_info() makes use of
bdev_get_queue() to determine the associated bdi given a block_device.

All the callers of bdev_get_queue() including
blk_get_backing_dev_info() assume that bdev_get_queue() may return
NULL and implement NULL handling; however, bdev_get_queue() requires
the passed in block_device is opened and attached to its gendisk.
Because an active gendisk always has a valid request_queue associated
with it, bdev_get_queue() can never return NULL and neither can
blk_get_backing_dev_info().

Make it clear that neither of the two functions can return NULL and
remove NULL handling from all the callers.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Chris Mason <clm@fb.com>
Cc: Dave Chinner <david@fromorbit.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

7 files changed, 5 insertions, 21 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 93603e6ff479..817446175489 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -83,18 +83,14 @@ void blk_queue_congestion_threshold(struct request_queue *q)
  * @bdev:       device
  *
  * Locates the passed device's request queue and returns the address of its
- * backing_dev_info
- *
- * Will return NULL if the request queue cannot be located.
+ * backing_dev_info.  This function can only be called if @bdev is opened
+ * and the return value is never NULL.
  */
 struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev)
 {
-        struct backing_dev_info *ret = NULL;
         struct request_queue *q = bdev_get_queue(bdev);
 
-        if (q)
-                ret = &q->backing_dev_info;
-        return ret;
+        return &q->backing_dev_info;
 }
 EXPORT_SYMBOL(blk_get_backing_dev_info);
 
diff --git a/block/compat_ioctl.c b/block/compat_ioctl.c
index 18b282ce361e..f678c733df40 100644
--- a/block/compat_ioctl.c
+++ b/block/compat_ioctl.c
@@ -709,8 +709,6 @@ long compat_blkdev_ioctl(struct file *file, unsigned cmd, unsigned long arg)
                 if (!arg)
                         return -EINVAL;
                 bdi = blk_get_backing_dev_info(bdev);
-                if (bdi == NULL)
-                        return -ENOTTY;
                 return compat_put_long(arg,
                                        (bdi->ra_pages * PAGE_CACHE_SIZE) / 512);
         case BLKROGET: /* compatible */
@@ -731,8 +729,6 @@ long compat_blkdev_ioctl(struct file *file, unsigned cmd, unsigned long arg)
                 if (!capable(CAP_SYS_ADMIN))
                         return -EACCES;
                 bdi = blk_get_backing_dev_info(bdev);
-                if (bdi == NULL)
-                        return -ENOTTY;
                 bdi->ra_pages = (arg * 512) / PAGE_CACHE_SIZE;
                 return 0;
         case BLKGETSIZE:
diff --git a/block/ioctl.c b/block/ioctl.c
index d6cda8147c91..6c7bf903742f 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -356,8 +356,6 @@ int blkdev_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
                 if (!arg)
                         return -EINVAL;
                 bdi = blk_get_backing_dev_info(bdev);
-                if (bdi == NULL)
-                        return -ENOTTY;
                 return put_long(arg, (bdi->ra_pages * PAGE_CACHE_SIZE) / 512);
         case BLKROGET:
                 return put_int(arg, bdev_read_only(bdev) != 0);
@@ -386,8 +384,6 @@ int blkdev_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
                 if(!capable(CAP_SYS_ADMIN))
                         return -EACCES;
                 bdi = blk_get_backing_dev_info(bdev);
-                if (bdi == NULL)
-                        return -ENOTTY;
                 bdi->ra_pages = (arg * 512) / PAGE_CACHE_SIZE;
                 return 0;
         case BLKBSZSET:
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 6d7274619bf9..d3251eca6429 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1173,8 +1173,6 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
                         if (!ret) {
                                 bd_set_size(bdev,(loff_t)get_capacity(disk)<<9);
                                 bdi = blk_get_backing_dev_info(bdev);
-                                if (bdi == NULL)
-                                        bdi = &default_backing_dev_info;
                                 bdev_inode_switch_bdi(bdev->bd_inode, bdi);
                         }
 
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index d0ed9e664f7d..39ff591ae1b4 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1694,7 +1694,7 @@ static int btrfs_congested_fn(void *congested_data, int bdi_bits)
                 if (!device->bdev)
                         continue;
                 bdi = blk_get_backing_dev_info(device->bdev);
-                if (bdi && bdi_congested(bdi, bdi_bits)) {
+                if (bdi_congested(bdi, bdi_bits)) {
                         ret = 1;
                         break;
                 }
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index cd7b8ca9b064..497fcde381d7 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -1678,8 +1678,6 @@ xfs_alloc_buftarg(
         btp->bt_dev =  bdev->bd_dev;
         btp->bt_bdev = bdev;
         btp->bt_bdi = blk_get_backing_dev_info(bdev);
-        if (!btp->bt_bdi)
-                goto error;
 
         if (xfs_setsize_buftarg_early(btp, bdev))
                 goto error;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 518b46555b80..e267bf0db559 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -865,7 +865,7 @@ extern void blk_execute_rq_nowait(struct request_queue *, struct gendisk *,
 
 static inline struct request_queue *bdev_get_queue(struct block_device *bdev)
 {
-        return bdev->bd_disk->queue;
+        return bdev->bd_disk->queue;    /* this is never NULL */
 }
 
 /*