[PATCH] partition handling locking cleanups

Horrors with open/reread_partition exclusion are starting to get fixed.

It's not the final variant, but at least we are getting the logics into
one place; switch to final variant will happen once we get per-disk
analog of gendisks.  New fields - ->bd_part_sem and ->bd_part_count.

The latter counts the amount of opened partitions.  The former protects
said count _and_ is held while we are rereading partition tables.
Helpers - dev_part_lock()/dev_part_unlock() (currently taking kdev_t; that
will change pretty soon).  No more ->open() and ->release() for partitions,
all that logics went to generic code.  Lock hierachy is currently messy:

  ->bd_sem for partitions -> ->bd_part_sem -> ->bd_sem for entire disks

Ugly, but that'll go away and to get the final variant of locking right
now would take _really_ big patch - with a lot of steps glued together.
The damn thing is large as it is...

1 files changed, 30 insertions, 2 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 83f5a21b5d26..b58c1b43f734 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -342,7 +342,7 @@ struct block_device {
 	struct inode *		bd_inode;
 	dev_t			bd_dev;  /* not a kdev_t - it's a search key */
 	int			bd_openers;
-	const struct block_device_operations *bd_op;
+	struct block_device_operations *bd_op;
 	struct request_queue	*bd_queue;
 	struct semaphore	bd_sem;	/* open/close mutex */
 	struct list_head	bd_inodes;
@@ -351,6 +351,8 @@ struct block_device {
 	struct block_device *	bd_contains;
 	unsigned		bd_block_size;
 	unsigned long		bd_offset;
+	struct semaphore	bd_part_sem;
+	unsigned		bd_part_count;
 };
 
 struct inode {
@@ -1083,7 +1085,7 @@ extern void bd_release(struct block_device *);
 extern void blk_run_queues(void);
 
 /* fs/devices.c */
-extern const struct block_device_operations *get_blkfops(unsigned int);
+extern struct block_device_operations *get_blkfops(unsigned int);
 extern int register_chrdev(unsigned int, const char *, struct file_operations *);
 extern int unregister_chrdev(unsigned int, const char *);
 extern int chrdev_open(struct inode *, struct file *);
@@ -1293,5 +1295,31 @@ static inline ino_t parent_ino(struct dentry *dentry)
 	return res;
 }
 
+/* NOTE NOTE NOTE: this interface _will_ change in a couple of patches */
+
+static inline int dev_lock_part(kdev_t dev)
+{
+	struct block_device *bdev = bdget(kdev_t_to_nr(dev));
+	if (!bdev)
+		return -ENOMEM;
+	if (!down_trylock(&bdev->bd_part_sem)) {
+		if (!bdev->bd_part_count)
+			return 0;
+		up(&bdev->bd_part_sem);
+	}
+	bdput(bdev);
+	return -EBUSY;
+}
+
+static inline void dev_unlock_part(kdev_t dev)
+{
+	struct block_device *bdev = bdget(kdev_t_to_nr(dev));
+	if (!bdev)
+		BUG();
+	up(&bdev->bd_part_sem);
+	bdput(bdev);
+	bdput(bdev);
+}
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_FS_H */