Re: [PATCH v8 06/19] block, fs: Propagate write hints to the block device inode

[Bart Van Assche <bvanassche@acm.org>]

On 1/3/24 01:02, Christoph Hellwig wrote:
> So you can use file->f_mapping->inode as I said in my previous mail.

Since struct address_space does not have a member with the name "inode",
I assume that you meant "host" instead of "inode"? If so, how about
modifying patch 06 of this series as shown below? With the patch below
my tests still pass.

Thanks,

Bart.


---
  block/fops.c       | 11 -----------
  fs/fcntl.c         | 15 +++++++++++----
  include/linux/fs.h |  1 -
  3 files changed, 11 insertions(+), 16 deletions(-)

diff --git a/block/fops.c b/block/fops.c
index 138b388b5cb1..787ce52bc2c6 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -620,16 +620,6 @@ 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)
  {
@@ -864,7 +854,6 @@ 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 18407bf5bb9b..cfb52c3a4577 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -306,7 +306,6 @@ 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;
@@ -318,11 +317,19 @@ 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);

+	/*
+	 * file->f_mapping->host may differ from inode. As an example,
+	 * blkdev_open() modifies file->f_mapping.
+	 */
+	if (file->f_mapping->host != inode) {
+		inode = file->f_mapping->host;
+		inode_lock(inode);
+		inode->i_write_hint = hint;
+		inode_unlock(inode);
+	}
+
  	return 0;
  }

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 293017ea2466..a08014b68d6e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1944,7 +1944,6 @@ 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 */