How to get sender's IP address and port number after io_uring_wait_cqe()?

[cnbatch]

When using recvfrom or recvmsg, the sender's IP address and port number can be retrieved from a struct sockaddr_in * or struct sockaddr_in6 *.

Now I'm reading the source file test/send_recvmsg.c , but I have not find a way to get that address after io_uring_wait_cqe(ring, &cqe) in static int do_recvmsg(struct io_uring *ring, char buf[MAX_MSG + 1], struct recv_data *rd).

After calling io_uring_wait_cqe(), cqe->user_data is still NULL.

So how can I get the sender's IP address and port numbers or struct sockaddr_in * (or struct sockaddr_in6 *) after io_uring_wait_cqe()?

Thanks in advance.

[ammarfaizi2]

I personally love the simplicity of the recvfrom / sendto API to handle
this case.

But io_uring doesn't have them. I wonder why do we support recv / send,
but not recvfrom / sendto. Life would be much better if we support the
latter because it's the superset of the former. And we don't actually have
recv / send syscall in the net/ anyway.

Yeah, I know, we already have recvmsg and sendmsg, but the data structure
is overkill for a simple thing like this.

So, you can read man 2 recvmsg for the detail. The function prototype of
recvmsg is:

ssize_t recvmsg(int sockfd, struct msghdr *msg, int flags);

That's what we have in io_uring_prep_recvmsg() as well, with the extra first
argument being the SQE to be submitted.

And then we have these two structs:

struct iovec {                    /* Scatter/gather array items */
    void  *iov_base;              /* Starting address */
    size_t iov_len;               /* Number of bytes to transfer */
};

struct msghdr {
    void         *msg_name;       /* optional address */
    socklen_t     msg_namelen;    /* size of address */
    struct iovec *msg_iov;        /* scatter/gather array */
    size_t        msg_iovlen;     /* # elements in msg_iov */
    void         *msg_control;    /* ancillary data, see below */
    size_t        msg_controllen; /* ancillary data buffer len */
    int           msg_flags;      /* flags on received message */
};

(Note, the recvmsg's second argument expects the type to be a pointer to
struct msghdr).

TL;DR

By using recvfrom, you must be usually doing this:

int fd = ...;
int flags = ...;
struct sockaddr_in addr;
socklen_t len = sizeof(addr);
char buf[N];
ssize_t ret;

ret = recvfrom(fd, buf, sizeof(buf), flags, (struct sockaddr *)&addr, &len);

the above call is equivalent to:

int fd = ...;
int flags = ...;
struct sockaddr_in addr;
socklen_t len = sizeof(addr);
char buf[N];
struct msghdr msg;
struct iovec iov;
ssize_t ret;

iov.iov_base = buf;
iov.iov_len = sizeof(buf);
msg.msg_name = &addr;
msg.msg_namelen = len;
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
msg.msg_control = NULL;
msg.msg_controllen = 0;
msg.msg_flags = 0;
ret = recvmsg(fd, &msg, flags);