[PATCH v2 08/25] io_uring: add io_uring_cmd_fixed_index_get() and io_uring_cmd_fixed_index_put()

[Joanne Koong <joannelkoong@gmail.com>]

Add two new helpers, io_uring_cmd_fixed_index_get() and
io_uring_cmd_fixed_index_put(). io_uring_cmd_fixed_index_get()
constructs an iter for a fixed buffer at a given index and acquires a
refcount on the underlying node. io_uring_cmd_fixed_index_put()
decrements this refcount. The caller is responsible for ensuring
io_uring_cmd_fixed_index_put() is properly called for releasing the
refcount after it is done using the iter it obtained through
io_uring_cmd_fixed_index_get().

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 buf index set on the sqe.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 include/linux/io_uring/cmd.h | 20 +++++++++++
 io_uring/rsrc.c              | 65 ++++++++++++++++++++++++++++++++++++
 io_uring/rsrc.h              |  5 +++
 io_uring/uring_cmd.c         | 21 ++++++++++++
 4 files changed, 111 insertions(+)

diff --git a/include/linux/io_uring/cmd.h b/include/linux/io_uring/cmd.h
index 7169a2a9a744..2988592e045c 100644
--- a/include/linux/io_uring/cmd.h
+++ b/include/linux/io_uring/cmd.h
@@ -44,6 +44,12 @@ 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_fixed_index_get(struct io_uring_cmd *ioucmd, u16 buf_index,
+				 unsigned int off, size_t len, int ddir,
+				 struct iov_iter *iter,
+				 unsigned int issue_flags);
+int io_uring_cmd_fixed_index_put(struct io_uring_cmd *ioucmd, u16 buf_index,
+				 unsigned int issue_flags);
 
 /*
  * Completes the request, i.e. posts an io_uring CQE and deallocates @ioucmd
@@ -109,6 +115,20 @@ static inline int io_uring_cmd_import_fixed_vec(struct io_uring_cmd *ioucmd,
 {
 	return -EOPNOTSUPP;
 }
+static inline int io_uring_cmd_fixed_index_get(struct io_uring_cmd *ioucmd,
+					       u16 buf_index, unsigned int off,
+					       size_t len, int ddir,
+					       struct iov_iter *iter,
+					       unsigned int issue_flags)
+{
+	return -EOPNOTSUPP;
+}
+static inline int io_uring_cmd_fixed_index_put(struct io_uring_cmd *ioucmd,
+					       u16 buf_index,
+					       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 a63474b331bf..a141aaeb099d 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -1151,6 +1151,71 @@ 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_reg_buf_index_get(struct io_kiocb *req, struct iov_iter *iter,
+			 u16 buf_index, unsigned int off, size_t len,
+			 int ddir, unsigned issue_flags)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+	struct io_rsrc_node *node;
+	struct io_mapped_ubuf *imu;
+	u64 addr;
+	int err;
+
+	io_ring_submit_lock(ctx, issue_flags);
+
+	node = io_rsrc_node_lookup(&ctx->buf_table, buf_index);
+	if (!node) {
+		io_ring_submit_unlock(ctx, issue_flags);
+		return -EINVAL;
+	}
+
+	node->refs++;
+
+	io_ring_submit_unlock(ctx, issue_flags);
+
+	imu = node->buf;
+	if (!imu) {
+		err = -EFAULT;
+		goto error;
+	}
+
+	if (check_add_overflow(imu->ubuf, off, &addr)) {
+		err = -EINVAL;
+		goto error;
+	}
+
+	err = io_import_fixed(ddir, iter, imu, addr, len);
+	if (err)
+		goto error;
+
+	return 0;
+
+error:
+	io_reg_buf_index_put(req, buf_index, issue_flags);
+	return err;
+}
+
+int io_reg_buf_index_put(struct io_kiocb *req, u16 buf_index,
+			 unsigned issue_flags)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+	struct io_rsrc_node *node;
+
+	io_ring_submit_lock(ctx, issue_flags);
+
+	node = io_rsrc_node_lookup(&ctx->buf_table, buf_index);
+	if (WARN_ON_ONCE(!node)) {
+		io_ring_submit_unlock(ctx, issue_flags);
+		return -EFAULT;
+	}
+
+	io_put_rsrc_node(ctx, node);
+
+	io_ring_submit_unlock(ctx, issue_flags);
+
+	return 0;
+}
+
 /* 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..16f4bab9582b 100644
--- a/io_uring/rsrc.h
+++ b/io_uring/rsrc.h
@@ -64,6 +64,11 @@ 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_reg_buf_index_get(struct io_kiocb *req, struct iov_iter *iter,
+			 u16 buf_index, unsigned int off, size_t len,
+			 int ddir, unsigned issue_flags);
+int io_reg_buf_index_put(struct io_kiocb *req, u16 buf_index,
+			 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 b6b675010bfd..ee95d1102505 100644
--- a/io_uring/uring_cmd.c
+++ b/io_uring/uring_cmd.c
@@ -314,6 +314,27 @@ 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_fixed_index_get(struct io_uring_cmd *ioucmd, u16 buf_index,
+				 unsigned int off, size_t len, int ddir,
+				 struct iov_iter *iter,
+				 unsigned int issue_flags)
+{
+	struct io_kiocb *req = cmd_to_io_kiocb(ioucmd);
+
+	return io_reg_buf_index_get(req, iter, buf_index, off, len, ddir,
+				    issue_flags);
+}
+EXPORT_SYMBOL_GPL(io_uring_cmd_fixed_index_get);
+
+int io_uring_cmd_fixed_index_put(struct io_uring_cmd *ioucmd, u16 buf_index,
+				 unsigned int issue_flags)
+{
+	struct io_kiocb *req = cmd_to_io_kiocb(ioucmd);
+
+	return io_reg_buf_index_put(req, buf_index, issue_flags);
+}
+EXPORT_SYMBOL_GPL(io_uring_cmd_fixed_index_put);
+
 void io_uring_cmd_issue_blocking(struct io_uring_cmd *ioucmd)
 {
 	struct io_kiocb *req = cmd_to_io_kiocb(ioucmd);
-- 
2.47.3