[PATCH v1 09/30] io_uring: add io_uring_cmd_import_fixed_index()

[Joanne Koong <joannelkoong@gmail.com>]

Add a new helper, io_uring_cmd_import_fixed_index(). This takes in a
buffer index. This requires the buffer table to have been pinned
beforehand. The caller is responsible for ensuring it does not use the
returned iter after the buffer table has been unpinned.

This is a preparatory patch needed for fuse-over-io-uring support, as
the metadata for fuse requests will be stored at the last index, which
will be different from the sqe's buffer index.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 include/linux/io_uring/cmd.h | 10 ++++++++++
 io_uring/rsrc.c              | 31 +++++++++++++++++++++++++++++++
 io_uring/rsrc.h              |  2 ++
 io_uring/uring_cmd.c         | 11 +++++++++++
 4 files changed, 54 insertions(+)

diff --git a/include/linux/io_uring/cmd.h b/include/linux/io_uring/cmd.h
index 375fd048c4cb..a4b5eae2e5d1 100644
--- a/include/linux/io_uring/cmd.h
+++ b/include/linux/io_uring/cmd.h
@@ -44,6 +44,9 @@ int io_uring_cmd_import_fixed_vec(struct io_uring_cmd *ioucmd,
 				  size_t uvec_segs,
 				  int ddir, struct iov_iter *iter,
 				  unsigned issue_flags);
+int io_uring_cmd_import_fixed_index(struct io_uring_cmd *ioucmd, u16 buf_index,
+				    int ddir, struct iov_iter *iter,
+				    unsigned int issue_flags);
 
 /*
  * Completes the request, i.e. posts an io_uring CQE and deallocates @ioucmd
@@ -100,6 +103,13 @@ static inline int io_uring_cmd_import_fixed_vec(struct io_uring_cmd *ioucmd,
 {
 	return -EOPNOTSUPP;
 }
+static inline int io_uring_cmd_import_fixed_index(struct io_uring_cmd *ioucmd,
+						  u16 buf_index, int ddir,
+						  struct iov_iter *iter,
+						  unsigned int issue_flags)
+{
+	return -EOPNOTSUPP;
+}
 static inline void __io_uring_cmd_done(struct io_uring_cmd *cmd, s32 ret,
 		u64 ret2, unsigned issue_flags, bool is_cqe32)
 {
diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 67331cae0a5a..b6dd62118311 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -1156,6 +1156,37 @@ int io_import_reg_buf(struct io_kiocb *req, struct iov_iter *iter,
 	return io_import_fixed(ddir, iter, node->buf, buf_addr, len);
 }
 
+int io_import_reg_buf_index(struct io_kiocb *req, struct iov_iter *iter,
+			    u16 buf_index, int ddir, unsigned issue_flags)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+	struct io_rsrc_node *node;
+	struct io_mapped_ubuf *imu;
+
+	io_ring_submit_lock(ctx, issue_flags);
+
+	if (buf_index >= req->ctx->buf_table.nr ||
+	    !(ctx->buf_table.flags & IO_RSRC_DATA_PINNED)) {
+		io_ring_submit_unlock(ctx, issue_flags);
+		return -EINVAL;
+	}
+
+	/*
+	 * We don't have to grab the reference on the node because the buffer
+	 * table is pinned. The caller is responsible for ensuring the iter
+	 * isn't used after the buffer table has been unpinned.
+	 */
+	node = io_rsrc_node_lookup(&ctx->buf_table, buf_index);
+	io_ring_submit_unlock(ctx, issue_flags);
+
+	if (!node || !node->buf)
+		return -EFAULT;
+
+	imu = node->buf;
+
+	return io_import_fixed(ddir, iter, imu, imu->ubuf, imu->len);
+}
+
 /* Lock two rings at once. The rings must be different! */
 static void lock_two_rings(struct io_ring_ctx *ctx1, struct io_ring_ctx *ctx2)
 {
diff --git a/io_uring/rsrc.h b/io_uring/rsrc.h
index d603f6a47f5e..658934f4d3ff 100644
--- a/io_uring/rsrc.h
+++ b/io_uring/rsrc.h
@@ -64,6 +64,8 @@ struct io_rsrc_node *io_find_buf_node(struct io_kiocb *req,
 int io_import_reg_buf(struct io_kiocb *req, struct iov_iter *iter,
 			u64 buf_addr, size_t len, int ddir,
 			unsigned issue_flags);
+int io_import_reg_buf_index(struct io_kiocb *req, struct iov_iter *iter,
+			    u16 buf_index, int ddir, unsigned issue_flags);
 int io_import_reg_vec(int ddir, struct iov_iter *iter,
 			struct io_kiocb *req, struct iou_vec *vec,
 			unsigned nr_iovs, unsigned issue_flags);
diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
index 197474911f04..e077eba00efe 100644
--- a/io_uring/uring_cmd.c
+++ b/io_uring/uring_cmd.c
@@ -314,6 +314,17 @@ int io_uring_cmd_import_fixed_vec(struct io_uring_cmd *ioucmd,
 }
 EXPORT_SYMBOL_GPL(io_uring_cmd_import_fixed_vec);
 
+int io_uring_cmd_import_fixed_index(struct io_uring_cmd *ioucmd, u16 buf_index,
+				    int ddir, struct iov_iter *iter,
+				    unsigned int issue_flags)
+{
+	struct io_kiocb *req = cmd_to_io_kiocb(ioucmd);
+
+	return io_import_reg_buf_index(req, iter, buf_index, ddir,
+				       issue_flags);
+}
+EXPORT_SYMBOL_GPL(io_uring_cmd_import_fixed_index);
+
 void io_uring_cmd_issue_blocking(struct io_uring_cmd *ioucmd)
 {
 	struct io_kiocb *req = cmd_to_io_kiocb(ioucmd);
-- 
2.47.3