Use/fix ret_* helpers for certain libc functions

- use ret_usize() instead of ret_send_recv() for c::recvmsg(), as it
  always returns c::ssize_t
- use ret_usize() instead of ret_send_recv() for c::sendmsg(), as it
  always returns c::ssize_t
- change the ret_send_recv() used on OSes different than Windows,
  Redox, and wasi to take c::ssize_t as parameter, as it is what
  c::recv(), c::send(), c::recvfrom(), and c::sendto() return on
  most/all of those OSes

src/backend/libc/conv.rs

@@ -170,7 +170,7 @@ pub(super) fn send_recv_len(len: usize) -> i32 {
 /// Convert the return value of a `send` or `recv` call.
 #[cfg(not(any(windows, target_os = "redox", target_os = "wasi")))]
 #[inline]
-pub(super) fn ret_send_recv(len: isize) -> io::Result<usize> {
+pub(super) fn ret_send_recv(len: c::ssize_t) -> io::Result<usize> {
     ret_usize(len)
 }
 

src/backend/libc/net/syscalls.rs

@@ -7,7 +7,7 @@ use super::msghdr::with_xdp_msghdr;
 #[cfg(target_os = "linux")]
 use super::write_sockaddr::encode_sockaddr_xdp;
 use crate::backend::c;
-use crate::backend::conv::{borrowed_fd, ret, ret_owned_fd, ret_send_recv, send_recv_len};
+use crate::backend::conv::{borrowed_fd, ret, ret_owned_fd, ret_usize, ret_send_recv, send_recv_len};
 use crate::fd::{BorrowedFd, OwnedFd};
 use crate::io;
 #[cfg(target_os = "linux")]
@@ -329,7 +329,7 @@ pub(crate) fn recvmsg(
 
     with_recv_msghdr(&mut storage, iov, control, |msghdr| {
         let result = unsafe {
-            ret_send_recv(c::recvmsg(
+            ret_usize(c::recvmsg(
                 borrowed_fd(sockfd),
                 msghdr,
                 bitflags_bits!(msg_flags),
@@ -364,7 +364,7 @@ pub(crate) fn sendmsg(
     msg_flags: SendFlags,
 ) -> io::Result<usize> {
     with_noaddr_msghdr(iov, control, |msghdr| unsafe {
-        ret_send_recv(c::sendmsg(
+        ret_usize(c::sendmsg(
             borrowed_fd(sockfd),
             &msghdr,
             bitflags_bits!(msg_flags),
@@ -387,7 +387,7 @@ pub(crate) fn sendmsg_v4(
     msg_flags: SendFlags,
 ) -> io::Result<usize> {
     with_v4_msghdr(addr, iov, control, |msghdr| unsafe {
-        ret_send_recv(c::sendmsg(
+        ret_usize(c::sendmsg(
             borrowed_fd(sockfd),
             &msghdr,
             bitflags_bits!(msg_flags),
@@ -410,7 +410,7 @@ pub(crate) fn sendmsg_v6(
     msg_flags: SendFlags,
 ) -> io::Result<usize> {
     with_v6_msghdr(addr, iov, control, |msghdr| unsafe {
-        ret_send_recv(c::sendmsg(
+        ret_usize(c::sendmsg(
             borrowed_fd(sockfd),
             &msghdr,
             bitflags_bits!(msg_flags),
@@ -430,7 +430,7 @@ pub(crate) fn sendmsg_unix(
     msg_flags: SendFlags,
 ) -> io::Result<usize> {
     super::msghdr::with_unix_msghdr(addr, iov, control, |msghdr| unsafe {
-        ret_send_recv(c::sendmsg(
+        ret_usize(c::sendmsg(
             borrowed_fd(sockfd),
             &msghdr,
             bitflags_bits!(msg_flags),
@@ -447,7 +447,7 @@ pub(crate) fn sendmsg_xdp(
     msg_flags: SendFlags,
 ) -> io::Result<usize> {
     with_xdp_msghdr(addr, iov, control, |msghdr| unsafe {
-        ret_send_recv(c::sendmsg(
+        ret_usize(c::sendmsg(
             borrowed_fd(sockfd),
             &msghdr,
             bitflags_bits!(msg_flags),