[RFC PATCH 2/2] btrfs: ioctl: use registered buffer for IORING_URING_CMD_FIXED

[Sidong Yang <sidong.yang@furiosa.ai>]

This patch supports IORING_URING_CMD_FIXED flags in io-uring cmd. It
means that user provided buf_index in sqe that is registered before
submitting requests. In this patch, btrfs_uring_encoded_read() makes
iov_iter bvec type by checking the io-uring cmd flag. And there is
additional iou_vec field in btrfs_uring_priv for remaining bvecs
lifecycle.

Signed-off-by: Sidong Yang <sidong.yang@furiosa.ai>
---
 fs/btrfs/ioctl.c | 26 +++++++++++++++++++++-----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 6c18bad53cd3..586671eea622 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -4643,6 +4643,7 @@ struct btrfs_uring_priv {
 	struct page **pages;
 	unsigned long nr_pages;
 	struct kiocb iocb;
+	struct iou_vec iou_vec;
 	struct iovec *iov;
 	struct iov_iter iter;
 	struct extent_state *cached_state;
@@ -4711,6 +4712,8 @@ static void btrfs_uring_read_finished(struct io_uring_cmd *cmd, unsigned int iss
 
 	kfree(priv->pages);
 	kfree(priv->iov);
+	if (priv->iou_vec.iovec)
+		kfree(priv->iou_vec.iovec);
 	kfree(priv);
 }
 
@@ -4730,7 +4733,8 @@ static int btrfs_uring_read_extent(struct kiocb *iocb, struct iov_iter *iter,
 				   struct extent_state *cached_state,
 				   u64 disk_bytenr, u64 disk_io_size,
 				   size_t count, bool compressed,
-				   struct iovec *iov, struct io_uring_cmd *cmd)
+				   struct iovec *iov, struct io_uring_cmd *cmd,
+				   struct iou_vec *iou_vec)
 {
 	struct btrfs_inode *inode = BTRFS_I(file_inode(iocb->ki_filp));
 	struct extent_io_tree *io_tree = &inode->io_tree;
@@ -4767,6 +4771,7 @@ static int btrfs_uring_read_extent(struct kiocb *iocb, struct iov_iter *iter,
 	priv->start = start;
 	priv->lockend = lockend;
 	priv->err = 0;
+	priv->iou_vec = *iou_vec;
 
 	ret = btrfs_encoded_read_regular_fill_pages(inode, disk_bytenr,
 						    disk_io_size, pages, priv);
@@ -4818,6 +4823,7 @@ static int btrfs_uring_encoded_read(struct io_uring_cmd *cmd, unsigned int issue
 	u64 start, lockend;
 	void __user *sqe_addr;
 	struct btrfs_uring_encoded_data *data = io_uring_cmd_get_async_data(cmd)->op_data;
+	struct iou_vec iou_vec = {};
 
 	if (!capable(CAP_SYS_ADMIN)) {
 		ret = -EPERM;
@@ -4875,9 +4881,19 @@ static int btrfs_uring_encoded_read(struct io_uring_cmd *cmd, unsigned int issue
 		}
 
 		data->iov = data->iovstack;
-		ret = import_iovec(ITER_DEST, data->args.iov, data->args.iovcnt,
-				   ARRAY_SIZE(data->iovstack), &data->iov,
-				   &data->iter);
+
+		if (cmd && (cmd->flags & IORING_URING_CMD_FIXED)) {
+			ret = io_uring_cmd_import_fixed_vec(
+				data->args.iov, data->args.iovcnt, ITER_DEST,
+				&data->iter, cmd, &iou_vec, false, issue_flags);
+			data->iov = NULL;
+		} else {
+			ret = import_iovec(ITER_DEST, data->args.iov,
+					   data->args.iovcnt,
+					   ARRAY_SIZE(data->iovstack),
+					   &data->iov, &data->iter);
+		}
+
 		if (ret < 0)
 			goto out_acct;
 
@@ -4929,7 +4945,7 @@ static int btrfs_uring_encoded_read(struct io_uring_cmd *cmd, unsigned int issue
 		ret = btrfs_uring_read_extent(&kiocb, &data->iter, start, lockend,
 					      cached_state, disk_bytenr, disk_io_size,
 					      count, data->args.compression,
-					      data->iov, cmd);
+					      data->iov, cmd, &iou_vec);
 
 		goto out_acct;
 	}
-- 
2.43.0