[PATCH v5 3/8] fs: add i_write_stream, exclusive with the write life time hint

[Kanchan Joshi <joshi.k@samsung.com>]

Keep the attached stream id in the VFS inode rather than the
filesystem's own, so that fcntl_set_rw_hint() can see it. It is a u16 in
the 32-bit hole after i_state, so struct inode does not grow.

Suggested-by: Christoph Hellwig <hch@lst.de>
Suggested-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
---
 fs/fcntl.c         | 7 +++++++
 fs/inode.c         | 1 +
 include/linux/fs.h | 2 +-
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/fcntl.c b/fs/fcntl.c
index c158f082f1da..a5439e076197 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -380,7 +380,14 @@ static long fcntl_set_rw_hint(struct file *file, unsigned long arg)
 	if (!rw_hint_valid(hint))
 		return -EINVAL;
 
+	/* keep write stream and write life time hint mutually exclusive */
+	spin_lock(&inode->i_lock);
+	if (hint != WRITE_LIFE_NOT_SET && READ_ONCE(inode->i_write_stream)) {
+		spin_unlock(&inode->i_lock);
+		return -EBUSY;
+	}
 	WRITE_ONCE(inode->i_write_hint, hint);
+	spin_unlock(&inode->i_lock);
 
 	/*
 	 * file->f_mapping->host may differ from inode. As an example,
diff --git a/fs/inode.c b/fs/inode.c
index ba7da39be4a3..50b91d449a38 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -246,6 +246,7 @@ int inode_init_always_gfp(struct super_block *sb, struct inode *inode, gfp_t gfp
 	atomic_set(&inode->i_writecount, 0);
 	inode->i_size = 0;
 	inode->i_write_hint = WRITE_LIFE_NOT_SET;
+	inode->i_write_stream = 0;
 	inode->i_blocks = 0;
 	inode->i_bytes = 0;
 	inode->i_generation = 0;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index f9d1e05e8ae6..3d9ce4d30cd5 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -812,7 +812,7 @@ struct inode {
 
 	/* Misc */
 	struct inode_state_flags i_state;
-	/* 32-bit hole */
+	u16			i_write_stream;
 	struct rw_semaphore	i_rwsem;
 
 	unsigned long		dirtied_when;	/* jiffies of first dirtying */
-- 
2.25.1