[PATCH v6 07/20] block, fs: Propagate write hints to the block device inode

[Bart Van Assche <bvanassche@xxxxxxx>]

Write hints applied with F_SET_RW_HINT on a block device affect the
shmem inode only. Propagate these hints to the block device inode
because that is the inode used when writing back dirty pages.

Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Jeff Layton <jlayton@xxxxxxxxxx>
Cc: Chuck Lever <chuck.lever@xxxxxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
 block/fops.c       | 11 +++++++++++
 fs/fcntl.c         |  4 ++++
 include/linux/fs.h |  1 +
 3 files changed, 16 insertions(+)

diff --git a/block/fops.c b/block/fops.c
index 124a06c1b925..5560eb9d8b49 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -620,6 +620,16 @@ static int blkdev_release(struct inode *inode, struct file *filp)
 	return 0;
 }
 
+static void blkdev_apply_whint(struct file *file, enum rw_hint hint)
+{
+	struct bdev_handle *handle = file->private_data;
+	struct inode *bd_inode = handle->bdev->bd_inode;
+
+	inode_lock(bd_inode);
+	bd_inode->i_write_hint = hint;
+	inode_unlock(bd_inode);
+}
+
 static ssize_t
 blkdev_direct_write(struct kiocb *iocb, struct iov_iter *from)
 {
@@ -854,6 +864,7 @@ const struct file_operations def_blk_fops = {
 	.splice_read	= filemap_splice_read,
 	.splice_write	= iter_file_splice_write,
 	.fallocate	= blkdev_fallocate,
+	.apply_whint	= blkdev_apply_whint,
 };
 
 static __init int blkdev_init(void)
diff --git a/fs/fcntl.c b/fs/fcntl.c
index 8018c4da478c..1d97a60de22f 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -306,6 +306,7 @@ static long fcntl_get_rw_hint(struct file *file, unsigned int cmd,
 static long fcntl_set_rw_hint(struct file *file, unsigned int cmd,
 			      unsigned long arg)
 {
+	void (*apply_whint)(struct file *, enum rw_hint);
 	struct inode *inode = file_inode(file);
 	u64 __user *argp = (u64 __user *)arg;
 	u64 hint;
@@ -317,6 +318,9 @@ static long fcntl_set_rw_hint(struct file *file, unsigned int cmd,
 
 	inode_lock(inode);
 	inode->i_write_hint = hint;
+	apply_whint = inode->i_fop->apply_whint;
+	if (apply_whint)
+		apply_whint(file, hint);
 	inode_unlock(inode);
 
 	return 0;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index a6e0c4b5a72b..5ae943e717df 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1945,6 +1945,7 @@ struct file_operations {
 	int (*uring_cmd)(struct io_uring_cmd *ioucmd, unsigned int issue_flags);
 	int (*uring_cmd_iopoll)(struct io_uring_cmd *, struct io_comp_batch *,
 				unsigned int poll_flags);
+	void (*apply_whint)(struct file *, enum rw_hint hint);
 } __randomize_layout;
 
 /* Wrap a directory iterator that needs exclusive inode access */