fs: add a FMODE_ flag to indicate IOCB_HAS_METADATA availability

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: 4de2ce0 ("fs: introduce IOCB_HAS_METADATA for metadata")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/20250819082517.2038819-2-hch@lst.de
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Christoph Hellwig

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)

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))

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.