[PATCH RFC liburing 1/2] add multishot recvmsg API

[Dylan Yudaken <dylany@fb.com>]

This adds a new API to do multishot recvmsg. This is more complicated than
multishot recv as it requires handling a well known data layout copied by
the kernel.

Signed-off-by: Dylan Yudaken <dylany@fb.com>
---
 src/include/liburing.h          | 59 +++++++++++++++++++++++++++++++++
 src/include/liburing/io_uring.h |  7 ++++
 2 files changed, 66 insertions(+)

diff --git a/src/include/liburing.h b/src/include/liburing.h
index d35bfa9..3f18bd2 100644
--- a/src/include/liburing.h
+++ b/src/include/liburing.h
@@ -419,6 +419,13 @@ static inline void io_uring_prep_recvmsg(struct io_uring_sqe *sqe, int fd,
 	sqe->msg_flags = flags;
 }
 
+static inline void io_uring_prep_recvmsg_multishot(struct io_uring_sqe *sqe, int fd,
+						   struct msghdr *msg, unsigned flags)
+{
+	io_uring_prep_recvmsg(sqe, fd, msg, flags);
+	sqe->ioprio |= IORING_RECV_MULTISHOT;
+}
+
 static inline void io_uring_prep_sendmsg(struct io_uring_sqe *sqe, int fd,
 					 const struct msghdr *msg,
 					 unsigned flags)
@@ -685,6 +692,58 @@ static inline void io_uring_prep_recv_multishot(struct io_uring_sqe *sqe,
 	sqe->ioprio |= IORING_RECV_MULTISHOT;
 }
 
+static inline struct io_uring_recvmsg_out *io_uring_recvmsg_validate(
+	void *buf, int buf_len, struct msghdr *m)
+{
+	struct io_uring_recvmsg_out *ret;
+	size_t header = m->msg_controllen + m->msg_namelen + sizeof(struct io_uring_recvmsg_out);
+
+	if (buf_len < header)
+		return NULL;
+	ret = (struct io_uring_recvmsg_out *)buf;
+	if (buf_len < header + ret->payloadlen)
+		return NULL;
+	return ret;
+}
+
+static inline void *io_uring_recvmsg_name(struct io_uring_recvmsg_out *o)
+{
+	return (void*)&o[1];
+}
+
+static inline struct cmsghdr *io_uring_recvmsg_cmsg_firsthdr(struct io_uring_recvmsg_out *o,
+							     struct msghdr *m)
+{
+	if (o->controllen < sizeof(struct cmsghdr))
+		return NULL;
+	return (struct cmsghdr *)((unsigned char*)io_uring_recvmsg_name(o) + m->msg_namelen);
+}
+
+static inline void *io_uring_recvmsg_payload(struct io_uring_recvmsg_out *o,
+					     struct msghdr *m)
+{
+	return (void*)((unsigned char*)io_uring_recvmsg_name(o) + m->msg_namelen + m->msg_controllen);
+}
+
+static inline struct cmsghdr *io_uring_recvmsg_cmsg_nexthdr(struct io_uring_recvmsg_out *o,
+							    struct msghdr *m,
+							    struct cmsghdr *cmsg)
+{
+	unsigned char *end;
+
+	if (cmsg->cmsg_len < sizeof (struct cmsghdr))
+		return NULL;
+	end = (unsigned char *)io_uring_recvmsg_payload(o, m);
+	cmsg = (struct cmsghdr *)((unsigned char *)cmsg + CMSG_ALIGN(cmsg->cmsg_len));
+
+	if ((unsigned char *)(cmsg + 1) > end)
+		return NULL;
+	if (((unsigned char *)cmsg) + CMSG_ALIGN(cmsg->cmsg_len) > end)
+		return NULL;
+
+	return cmsg;
+}
+
 static inline void io_uring_prep_openat2(struct io_uring_sqe *sqe, int dfd,
 					const char *path, struct open_how *how)
 {
diff --git a/src/include/liburing/io_uring.h b/src/include/liburing/io_uring.h
index fbf6403..5e111b4 100644
--- a/src/include/liburing/io_uring.h
+++ b/src/include/liburing/io_uring.h
@@ -573,6 +573,13 @@ struct io_uring_file_index_range {
 	__u64	resv;
 };
 
+struct io_uring_recvmsg_out {
+	__u32 namelen;
+	__u32 controllen;
+	__u32 payloadlen;
+	__u32 flags;
+};
+
 /*
  * accept flags stored in sqe->ioprio
  */
-- 
2.30.2