[PATCH 3/8] bdev: infrastructure for flags

[Al Viro <viro@zeniv.linux.org.uk>]

Replace bd_partno with a 32bit field (__bd_flags).  The lower 8 bits
contain the partition number, the upper 24 are for flags.

Helpers: bdev_{test,set,clear}_flag(bdev, flag), where flag numbers
are zero-based.  Use cmpxchg() to set/clear - all architectures support
it for u32.

NOTE: this commit does not actuall move any flags over there - they
are still bool fields.  As the result, it shifts the fields wrt
cacheline boundaries; that's going to be restored once the first
3 flags are dealt with.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 block/bdev.c              |  2 +-
 include/linux/blk_types.h |  2 +-
 include/linux/blkdev.h    | 33 ++++++++++++++++++++++++++++++++-
 3 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/block/bdev.c b/block/bdev.c
index 7a5f611c3d2e..0c55f7abaac3 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -411,7 +411,7 @@ struct block_device *bdev_alloc(struct gendisk *disk, u8 partno)
 	mutex_init(&bdev->bd_fsfreeze_mutex);
 	spin_lock_init(&bdev->bd_size_lock);
 	mutex_init(&bdev->bd_holder_lock);
-	bdev->bd_partno = partno;
+	bdev->__bd_flags = partno;
 	bdev->bd_inode = inode;
 	bdev->bd_queue = disk->queue;
 	if (partno)
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index cb1526ec44b5..274f7eb4138f 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -45,8 +45,8 @@ struct block_device {
 	struct request_queue *	bd_queue;
 	struct disk_stats __percpu *bd_stats;
 	unsigned long		bd_stamp;
+	u32			__bd_flags;	// partition number + flags
 	bool			bd_read_only;	/* read-only policy */
-	u8			bd_partno;
 	bool			bd_write_holder;
 	bool			bd_has_submit_bio;
 	dev_t			bd_dev;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 32549d675955..b9dbfb811533 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -722,7 +722,38 @@ void disk_uevent(struct gendisk *disk, enum kobject_action action);
 
 static inline u8 bdev_partno(const struct block_device *bdev)
 {
-	return bdev->bd_partno;
+	return bdev->__bd_flags & 0xff;
+}
+
+static inline bool bdev_test_flag(const struct block_device *bdev, int flag)
+{
+	return bdev->__bd_flags & (1 << (flag + 8));
+}
+
+static inline void bdev_set_flag(struct block_device *bdev, int flag)
+{
+	u32 v = bdev->__bd_flags;
+
+	for (;;) {
+		u32 w = cmpxchg(&bdev->__bd_flags, v, v | (1 << (flag + 8)));
+
+		if (v == w)
+			return;
+		v = w;
+	}
+}
+
+static inline void bdev_clear_flag(struct block_device *bdev, int flag)
+{
+	u32 v = bdev->__bd_flags;
+
+	for (;;) {
+		u32 w = cmpxchg(&bdev->__bd_flags, v, v & ~(1 << (flag + 8)));
+
+		if (v == w)
+			return;
+		v = w;
+	}
 }
 
 static inline int get_disk_ro(struct gendisk *disk)
-- 
2.39.2