[PATCH 4/4] block: integrate bd_start_claiming into __blkdev_get

[Christoph Hellwig <hch@lst.de>]

bd_start_claiming duplicates a lot of the work done in __blkdev_get.
Integrate the two functions to avoid the duplicate work, and to do the
right thing for the md -ERESTARTSYS corner case.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/block_dev.c | 177 +++++++++++++++----------------------------------
 1 file changed, 55 insertions(+), 122 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 7075004d36997b..6fa987c77e0a1b 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1078,72 +1078,6 @@ static struct gendisk *bdev_get_gendisk(struct block_device *bdev, int *partno)
 	return disk;
 }
 
-/**
- * bd_start_claiming - start claiming a block device
- * @bdev: block device of interest
- * @holder: holder trying to claim @bdev
- *
- * @bdev is about to be opened exclusively.  Check @bdev can be opened
- * exclusively and mark that an exclusive open is in progress.  Each
- * successful call to this function must be matched with a call to
- * either bd_finish_claiming() or bd_abort_claiming() (which do not
- * fail).
- *
- * This function is used to gain exclusive access to the block device
- * without actually causing other exclusive open attempts to fail. It
- * should be used when the open sequence itself requires exclusive
- * access but may subsequently fail.
- *
- * CONTEXT:
- * Might sleep.
- *
- * RETURNS:
- * Pointer to the block device containing @bdev on success, ERR_PTR()
- * value on failure.
- */
-static struct block_device *bd_start_claiming(struct block_device *bdev,
-		void *holder)
-{
-	struct gendisk *disk;
-	struct block_device *whole;
-	int partno, err;
-
-	might_sleep();
-
-	/*
-	 * @bdev might not have been initialized properly yet, look up
-	 * and grab the outer block device the hard way.
-	 */
-	disk = bdev_get_gendisk(bdev, &partno);
-	if (!disk)
-		return ERR_PTR(-ENXIO);
-
-	/*
-	 * Normally, @bdev should equal what's returned from bdget_disk()
-	 * if partno is 0; however, some drivers (floppy) use multiple
-	 * bdev's for the same physical device and @bdev may be one of the
-	 * aliases.  Keep @bdev if partno is 0.  This means claimer
-	 * tracking is broken for those devices but it has always been that
-	 * way.
-	 */
-	if (partno)
-		whole = bdget_disk(disk, 0);
-	else
-		whole = bdgrab(bdev);
-
-	put_disk_and_module(disk);
-	if (!whole)
-		return ERR_PTR(-ENOMEM);
-
-	err = bd_prepare_to_claim(bdev, whole, holder);
-	if (err) {
-		bdput(whole);
-		return ERR_PTR(err);
-	}
-
-	return whole;
-}
-
 static void bd_clear_claiming(struct block_device *whole, void *holder)
 {
 	lockdep_assert_held(&bdev_lock);
@@ -1156,7 +1090,7 @@ static void bd_clear_claiming(struct block_device *whole, void *holder)
 /**
  * bd_finish_claiming - finish claiming of a block device
  * @bdev: block device of interest
- * @whole: whole block device (returned from bd_start_claiming())
+ * @whole: whole block device
  * @holder: holder that has claimed @bdev
  *
  * Finish exclusive open of a block device. Mark the device as exlusively
@@ -1182,7 +1116,7 @@ static void bd_finish_claiming(struct block_device *bdev,
 /**
  * bd_abort_claiming - abort claiming of a block device
  * @bdev: block device of interest
- * @whole: whole block device (returned from bd_start_claiming())
+ * @whole: whole block device
  * @holder: holder that has claimed @bdev
  *
  * Abort claiming of a block device when the exclusive open failed. This can be
@@ -1521,13 +1455,15 @@ EXPORT_SYMBOL_GPL(bdev_disk_changed);
  *    mutex_lock_nested(whole->bd_mutex, 1)
  */
 
-static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
+static int __blkdev_get(struct block_device *bdev, fmode_t mode, void *holder,
+		int for_part)
 {
+	struct block_device *whole = NULL, *claiming = NULL;
 	struct gendisk *disk;
 	int ret;
 	int partno;
 	int perm = 0;
-	bool first_open = false, need_restart;
+	bool first_open = false, unblock_events = true, need_restart;
 
 	if (mode & FMODE_READ)
 		perm |= MAY_READ;
@@ -1549,6 +1485,25 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
 	if (!disk)
 		goto out;
 
+	if (partno) {
+		whole = bdget_disk(disk, 0);
+		if (!whole) {
+			ret = -ENOMEM;
+			goto out_put_disk;
+		}
+	}
+
+	if (!for_part && (mode & FMODE_EXCL)) {
+		WARN_ON_ONCE(!holder);
+		if (whole)
+			claiming = whole;
+		else
+			claiming = bdev;
+		ret = bd_prepare_to_claim(bdev, claiming, holder);
+		if (ret)
+			goto out_put_whole;
+	}
+
 	disk_block_events(disk);
 	mutex_lock_nested(&bdev->bd_mutex, for_part);
 	if (!bdev->bd_openers) {
@@ -1592,18 +1547,11 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
 			if (ret)
 				goto out_clear;
 		} else {
-			struct block_device *whole;
-			whole = bdget_disk(disk, 0);
-			ret = -ENOMEM;
-			if (!whole)
-				goto out_clear;
 			BUG_ON(for_part);
-			ret = __blkdev_get(whole, mode, 1);
-			if (ret) {
-				bdput(whole);
+			ret = __blkdev_get(whole, mode, NULL, 1);
+			if (ret)
 				goto out_clear;
-			}
-			bdev->bd_contains = whole;
+			bdev->bd_contains = bdgrab(whole);
 			bdev->bd_part = disk_get_part(disk, partno);
 			if (!(disk->flags & GENHD_FL_UP) ||
 			    !bdev->bd_part || !bdev->bd_part->nr_sects) {
@@ -1632,11 +1580,30 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
 	bdev->bd_openers++;
 	if (for_part)
 		bdev->bd_part_count++;
+	if (claiming)
+		bd_finish_claiming(bdev, claiming, holder);
+
+	/*
+	 * Block event polling for write claims if requested.  Any write holder
+	 * makes the write_holder state stick until all are released.  This is
+	 * good enough and tracking individual writeable reference is too
+	 * fragile given the way @mode is used in blkdev_get/put().
+	 */
+	if (claiming && (mode & FMODE_WRITE) && !bdev->bd_write_holder &&
+	    (disk->flags & GENHD_FL_BLOCK_EVENTS_ON_EXCL_WRITE)) {
+		bdev->bd_write_holder = true;
+		unblock_events = false;
+	}
 	mutex_unlock(&bdev->bd_mutex);
-	disk_unblock_events(disk);
+
+	if (unblock_events)
+		disk_unblock_events(disk);
+
 	/* only one opener holds refs to the module and disk */
 	if (!first_open)
 		put_disk_and_module(disk);
+	if (whole)
+		bdput(whole);
 	return 0;
 
  out_clear:
@@ -1647,13 +1614,18 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
 		__blkdev_put(bdev->bd_contains, mode, 1);
 	bdev->bd_contains = NULL;
  out_unlock_bdev:
+	if (claiming)
+		bd_abort_claiming(bdev, claiming, holder);
 	mutex_unlock(&bdev->bd_mutex);
 	disk_unblock_events(disk);
+ out_put_whole:
+ 	if (whole)
+		bdput(whole);
+ out_put_disk:
 	put_disk_and_module(disk);
 	if (need_restart)
 		goto restart;
  out:
-
 	return ret;
 }
 
@@ -1678,50 +1650,11 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
  */
 int blkdev_get(struct block_device *bdev, fmode_t mode, void *holder)
 {
-	struct block_device *whole = NULL;
 	int res;
 
-	WARN_ON_ONCE((mode & FMODE_EXCL) && !holder);
-
-	if ((mode & FMODE_EXCL) && holder) {
-		whole = bd_start_claiming(bdev, holder);
-		if (IS_ERR(whole)) {
-			bdput(bdev);
-			return PTR_ERR(whole);
-		}
-	}
-
-	res = __blkdev_get(bdev, mode, 0);
-
-	if (whole) {
-		struct gendisk *disk = whole->bd_disk;
-
-		/* finish claiming */
-		mutex_lock(&bdev->bd_mutex);
-		if (!res)
-			bd_finish_claiming(bdev, whole, holder);
-		else
-			bd_abort_claiming(bdev, whole, holder);
-		/*
-		 * Block event polling for write claims if requested.  Any
-		 * write holder makes the write_holder state stick until
-		 * all are released.  This is good enough and tracking
-		 * individual writeable reference is too fragile given the
-		 * way @mode is used in blkdev_get/put().
-		 */
-		if (!res && (mode & FMODE_WRITE) && !bdev->bd_write_holder &&
-		    (disk->flags & GENHD_FL_BLOCK_EVENTS_ON_EXCL_WRITE)) {
-			bdev->bd_write_holder = true;
-			disk_block_events(disk);
-		}
-
-		mutex_unlock(&bdev->bd_mutex);
-		bdput(whole);
-	}
-
+	res =__blkdev_get(bdev, mode, holder, 0);
 	if (res)
 		bdput(bdev);
-
 	return res;
 }
 EXPORT_SYMBOL(blkdev_get);
-- 
2.26.2