block: clean up blkdev_get() wrappers and their users

After recent blkdev_get() modifications, open_by_devnum() and
open_bdev_exclusive() are simple wrappers around blkdev_get().
Replace them with blkdev_get_by_dev() and blkdev_get_by_path().

blkdev_get_by_dev() is identical to open_by_devnum().
blkdev_get_by_path() is slightly different in that it doesn't
automatically add %FMODE_EXCL to @mode.

All users are converted.  Most conversions are mechanical and don't
introduce any behavior difference.  There are several exceptions.

* btrfs now sets FMODE_EXCL in btrfs_device->mode, so there's no
  reason to OR it explicitly on blkdev_put().

* gfs2, nilfs2 and the generic mount_bdev() now set FMODE_EXCL in
  sb->s_mode.

* With the above changes, sb->s_mode now always should contain
  FMODE_EXCL.  WARN_ON_ONCE() added to kill_block_super() to detect
  errors.

The new blkdev_get_*() functions are with proper docbook comments.
While at it, add function description to blkdev_get() too.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Philipp Reisner <philipp.reisner@linbit.com>
Cc: Neil Brown <neilb@suse.de>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: Joern Engel <joern@lazybastard.org>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Jan Kara <jack@suse.cz>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: KONISHI Ryusuke <konishi.ryusuke@lab.ntt.co.jp>
Cc: reiserfs-devel@vger.kernel.org
Cc: xfs-masters@oss.sgi.com
Cc: Alexander Viro <viro@zeniv.linux.org.uk>

18 files changed, 149 insertions, 94 deletions

diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
index fd0346090289..650e43ba4f7c 100644
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -902,8 +902,8 @@ static int drbd_nl_disk_conf(struct drbd_conf *mdev, struct drbd_nl_cfg_req *nlp
                 }
         }
 
-        bdev = open_bdev_exclusive(nbc->dc.backing_dev,
-                                   FMODE_READ | FMODE_WRITE, mdev);
+        bdev = blkdev_get_by_path(nbc->dc.backing_dev,
+                                  FMODE_READ | FMODE_WRITE | FMODE_EXCL, mdev);
         if (IS_ERR(bdev)) {
                 dev_err(DEV, "open(\"%s\") failed with %ld\n", nbc->dc.backing_dev,
                         PTR_ERR(bdev));
@@ -920,10 +920,10 @@ static int drbd_nl_disk_conf(struct drbd_conf *mdev, struct drbd_nl_cfg_req *nlp
          * should check it for you already; but if you don't, or
          * someone fooled it, we need to double check here)
          */
-        bdev = open_bdev_exclusive(nbc->dc.meta_dev,
-                                   FMODE_READ | FMODE_WRITE,
-                                   (nbc->dc.meta_dev_idx < 0) ?
-                                   (void *)mdev : (void *)drbd_m_holder);
+        bdev = blkdev_get_by_path(nbc->dc.meta_dev,
+                                  FMODE_READ | FMODE_WRITE | FMODE_EXCL,
+                                  (nbc->dc.meta_dev_idx < 0) ?
+                                  (void *)mdev : (void *)drbd_m_holder);
         if (IS_ERR(bdev)) {
                 dev_err(DEV, "open(\"%s\") failed with %ld\n", nbc->dc.meta_dev,
                         PTR_ERR(bdev));
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 9e88ca0c55e9..67150c32986c 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -325,7 +325,7 @@ static int open_dev(struct dm_dev_internal *d, dev_t dev,
 
         BUG_ON(d->dm_dev.bdev);
 
-        bdev = open_by_devnum(dev, d->dm_dev.mode | FMODE_EXCL, _claim_ptr);
+        bdev = blkdev_get_by_dev(dev, d->dm_dev.mode | FMODE_EXCL, _claim_ptr);
         if (IS_ERR(bdev))
                 return PTR_ERR(bdev);
 
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 6af951ffe0bb..5aaa6bfbe638 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1934,8 +1934,8 @@ static int lock_rdev(mdk_rdev_t *rdev, dev_t dev, int shared)
         struct block_device *bdev;
         char b[BDEVNAME_SIZE];
 
-        bdev = open_by_devnum(dev, FMODE_READ|FMODE_WRITE|FMODE_EXCL,
-                              shared ? (mdk_rdev_t *)lock_rdev : rdev);
+        bdev = blkdev_get_by_dev(dev, FMODE_READ|FMODE_WRITE|FMODE_EXCL,
+                                 shared ? (mdk_rdev_t *)lock_rdev : rdev);
         if (IS_ERR(bdev)) {
                 printk(KERN_ERR "md: could not open %s.\n",
                         __bdevname(dev, b));
diff --git a/drivers/mtd/devices/block2mtd.c b/drivers/mtd/devices/block2mtd.c
index aa557beb8f51..f29a6f9df6e7 100644
--- a/drivers/mtd/devices/block2mtd.c
+++ b/drivers/mtd/devices/block2mtd.c
@@ -247,7 +247,7 @@ static struct block2mtd_dev *add_device(char *devname, int erase_size)
                 return NULL;
 
         /* Get a handle on the device */
-        bdev = open_bdev_exclusive(devname, mode, dev);
+        bdev = blkdev_get_by_path(devname, mode, dev);
 #ifndef MODULE
         if (IS_ERR(bdev)) {
 
@@ -256,7 +256,7 @@ static struct block2mtd_dev *add_device(char *devname, int erase_size)
 
                 dev_t devt = name_to_dev_t(devname);
                 if (devt)
-                        bdev = open_by_devnum(devt, mode, dev);
+                        bdev = blkdev_get_by_dev(devt, mode, dev);
         }
 #endif
 
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 606a5259f87f..c1c1b8c3fb99 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -854,24 +854,6 @@ static inline void bd_unlink_disk_holder(struct block_device *bdev)
 { }
 #endif
 
-/*
- * Tries to open block device by device number.  Use it ONLY if you
- * really do not have anything better - i.e. when you are behind a
- * truly sucky interface and all you are given is a device number.  _Never_
- * to be used for internal purposes.  If you ever need it - reconsider
- * your API.
- */
-struct block_device *open_by_devnum(dev_t dev, fmode_t mode, void *holder)
-{
-        struct block_device *bdev = bdget(dev);
-        int err = -ENOMEM;
-        if (bdev)
-                err = blkdev_get(bdev, mode, holder);
-        return err ? ERR_PTR(err) : bdev;
-}
-
-EXPORT_SYMBOL(open_by_devnum);
-
 /**
  * flush_disk - invalidates all buffer-cache entries on a disk
  *
@@ -1132,6 +1114,25 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
         return ret;
 }
 
+/**
+ * blkdev_get - open a block device
+ * @bdev: block_device to open
+ * @mode: FMODE_* mask
+ * @holder: exclusive holder identifier
+ *
+ * Open @bdev with @mode.  If @mode includes %FMODE_EXCL, @bdev is
+ * open with exclusive access.  Specifying %FMODE_EXCL with %NULL
+ * @holder is invalid.  Exclusive opens may nest for the same @holder.
+ *
+ * On success, the reference count of @bdev is unchanged.  On failure,
+ * @bdev is put.
+ *
+ * CONTEXT:
+ * Might sleep.
+ *
+ * RETURNS:
+ * 0 on success, -errno on failure.
+ */
 int blkdev_get(struct block_device *bdev, fmode_t mode, void *holder)
 {
         struct block_device *whole = NULL;
@@ -1186,6 +1187,80 @@ int blkdev_get(struct block_device *bdev, fmode_t mode, void *holder)
 }
 EXPORT_SYMBOL(blkdev_get);
 
+/**
+ * blkdev_get_by_path - open a block device by name
+ * @path: path to the block device to open
+ * @mode: FMODE_* mask
+ * @holder: exclusive holder identifier
+ *
+ * Open the blockdevice described by the device file at @path.  @mode
+ * and @holder are identical to blkdev_get().
+ *
+ * On success, the returned block_device has reference count of one.
+ *
+ * CONTEXT:
+ * Might sleep.
+ *
+ * RETURNS:
+ * Pointer to block_device on success, ERR_PTR(-errno) on failure.
+ */
+struct block_device *blkdev_get_by_path(const char *path, fmode_t mode,
+                                        void *holder)