Re: [PATCH 1/2] fs: add a FMODE_ flag to indicate IOCB_HAS_METADATA availability

[Christian Brauner <brauner@kernel.org>]

On Tue, Aug 19, 2025 at 10:25:00AM +0200, Christoph Hellwig wrote:
> Currently the kernel will happily route io_uring requests with metadata
> to file operations that don't support it.  Add a FMODE_ flag to guard
> that.
> 
> Fixes: 4de2ce04c862 ("fs: introduce IOCB_HAS_METADATA for metadata")
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---

It kind of feels like that f_iocb_flags should be changed so that
subsystems like block can just raise some internal flags directly
instead of grabbing a f_mode flag everytime they need to make some
IOCB_* flag conditional on the file. That would mean changing the
unconditional assigment to file->f_iocb_flags to a |= to not mask flags
raised by the kernel itself.

Then you can just push the burden of stuff like IOCB_HAS_* vs
IOCB_SUPPORTS/CAN_* to f_iocb_flags instead of the FMODE_* space.

>  block/fops.c       | 3 +++
>  include/linux/fs.h | 3 ++-
>  io_uring/rw.c      | 3 +++
>  3 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/block/fops.c b/block/fops.c
> index 82451ac8ff25..08e7c21bd9f1 100644
> --- a/block/fops.c
> +++ b/block/fops.c
> @@ -7,6 +7,7 @@
>  #include <linux/init.h>
>  #include <linux/mm.h>
>  #include <linux/blkdev.h>
> +#include <linux/blk-integrity.h>
>  #include <linux/buffer_head.h>
>  #include <linux/mpage.h>
>  #include <linux/uio.h>
> @@ -687,6 +688,8 @@ static int blkdev_open(struct inode *inode, struct file *filp)
>  
>  	if (bdev_can_atomic_write(bdev))
>  		filp->f_mode |= FMODE_CAN_ATOMIC_WRITE;
> +	if (blk_get_integrity(bdev->bd_disk))
> +		filp->f_mode |= FMODE_HAS_METADATA;
>  
>  	ret = bdev_open(bdev, mode, filp->private_data, NULL, filp);
>  	if (ret)
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index d7ab4f96d705..601d036a6c78 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -149,7 +149,8 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
>  /* Expect random access pattern */
>  #define FMODE_RANDOM		((__force fmode_t)(1 << 12))
>  
> -/* FMODE_* bit 13 */
> +/* Supports IOCB_HAS_METADATA */
> +#define FMODE_HAS_METADATA	((__force fmode_t)(1 << 13))
>  
>  /* File is opened with O_PATH; almost nothing can be done with it */
>  #define FMODE_PATH		((__force fmode_t)(1 << 14))
> diff --git a/io_uring/rw.c b/io_uring/rw.c
> index 52a5b950b2e5..af5a54b5db12 100644
> --- a/io_uring/rw.c
> +++ b/io_uring/rw.c
> @@ -886,6 +886,9 @@ static int io_rw_init_file(struct io_kiocb *req, fmode_t mode, int rw_type)
>  	if (req->flags & REQ_F_HAS_METADATA) {
>  		struct io_async_rw *io = req->async_data;
>  
> +		if (!(file->f_mode & FMODE_HAS_METADATA))
> +			return -EINVAL;
> +
>  		/*
>  		 * We have a union of meta fields with wpq used for buffered-io
>  		 * in io_async_rw, so fail it here.
> -- 
> 2.47.2
>