Consolidate CMSG_* implementations

The original intent was to simplify the reasoning for how they
differ across platforms. It should as a consequence also make it
easier to extend target support.

Changes:

- CMSG_* functions which can be const are all marked const.
- Removes unsafe from `CMSG_ALIGN`, `CMSG_SPACE`, `CMSG_LEN`.

Fixes:

Custom CMSG_FIRSTHDR implementation for VxWorks had missed to check
that `mhdr.msg_controllen >= size_of::<cmsghdr>()`, as per
POSIX 1003.1-2024.

Documents:

- Usage and safety requirements.
- Adds missing references to upstream headers.

Author: gibbz00

libc-test/tests/cmsg.rs

@@ -3,11 +3,9 @@
 
 #[cfg(unix)]
 mod t {
-
     use std::mem;
 
     use libc::{
-        self,
         c_uchar,
         c_uint,
         c_void,
@@ -50,9 +48,7 @@ mod t {
     #[test]
     fn test_cmsg_len() {
         for l in 0..128 {
-            unsafe {
-                assert_eq!(libc::CMSG_LEN(l) as usize, cmsg_len(l));
-            }
+            assert_eq!(libc::CMSG_LEN(l) as usize, unsafe { cmsg_len(l) });
         }
     }
 
@@ -108,10 +104,8 @@ mod t {
 
     #[test]
     fn test_cmsg_space() {
-        unsafe {
-            for l in 0..128 {
-                assert_eq!(libc::CMSG_SPACE(l) as usize, cmsg_space(l));
-            }
+        for l in 0..128 {
+            assert_eq!(libc::CMSG_SPACE(l) as usize, unsafe { cmsg_space(l) });
         }
     }
 }

src/fuchsia/mod.rs

@@ -3000,6 +3000,8 @@ pub const O_NOFOLLOW: c_int = 0x00000080;
 pub const HUGETLB_FLAG_ENCODE_SHIFT: u32 = 26;
 pub const MAP_HUGE_SHIFT: u32 = 26;
 
+// END_PUB_CONST
+
 // intentionally not public, only used for fd_set
 cfg_if! {
     if #[cfg(target_pointer_width = "32")] {
@@ -3011,8 +3013,6 @@ cfg_if! {
     }
 }
 
-// END_PUB_CONST
-
 f! {
     pub fn FD_CLR(fd: c_int, set: *mut fd_set) -> () {
         let fd = fd as usize;
@@ -3069,40 +3069,6 @@ f! {
     pub fn CPU_EQUAL(set1: &cpu_set_t, set2: &cpu_set_t) -> bool {
         set1.bits == set2.bits
     }
-
-    pub fn CMSG_DATA(cmsg: *const cmsghdr) -> *mut c_uchar {
-        cmsg.offset(1) as *mut c_uchar
-    }
-
-    pub fn CMSG_NXTHDR(mhdr: *const msghdr, cmsg: *const cmsghdr) -> *mut cmsghdr {
-        if ((*cmsg).cmsg_len as size_t) < size_of::<cmsghdr>() {
-            core::ptr::null_mut::<cmsghdr>()
-        } else if __CMSG_NEXT(cmsg).add(size_of::<cmsghdr>()) >= __MHDR_END(mhdr) {
-            core::ptr::null_mut::<cmsghdr>()
-        } else {
-            __CMSG_NEXT(cmsg).cast()
-        }
-    }
-
-    pub fn CMSG_FIRSTHDR(mhdr: *const msghdr) -> *mut cmsghdr {
-        if (*mhdr).msg_controllen as size_t >= size_of::<cmsghdr>() {
-            (*mhdr).msg_control.cast()
-        } else {
-            core::ptr::null_mut::<cmsghdr>()
-        }
-    }
-
-    pub const fn CMSG_ALIGN(len: size_t) -> size_t {
-        (len + size_of::<size_t>() - 1) & !(size_of::<size_t>() - 1)
-    }
-
-    pub const fn CMSG_SPACE(len: c_uint) -> c_uint {
-        (CMSG_ALIGN(len as size_t) + CMSG_ALIGN(size_of::<cmsghdr>())) as c_uint
-    }
-
-    pub const fn CMSG_LEN(len: c_uint) -> c_uint {
-        (CMSG_ALIGN(size_of::<cmsghdr>()) + len as size_t) as c_uint
-    }
 }
 
 safe_f! {
@@ -3168,19 +3134,6 @@ safe_f! {
     }
 }
 
-fn __CMSG_LEN(cmsg: *const cmsghdr) -> ssize_t {
-    ((unsafe { (*cmsg).cmsg_len as size_t } + size_of::<c_long>() - 1) & !(size_of::<c_long>() - 1))
-        as ssize_t
-}
-
-fn __CMSG_NEXT(cmsg: *const cmsghdr) -> *mut c_uchar {
-    (unsafe { cmsg.offset(__CMSG_LEN(cmsg)) }) as *mut c_uchar
-}
-
-fn __MHDR_END(mhdr: *const msghdr) -> *mut c_uchar {
-    unsafe { (*mhdr).msg_control.offset((*mhdr).msg_controllen as isize) }.cast()
-}
-
 // EXTERN_FN
 
 #[link(name = "c")]

src/new/aix/mod.rs

@@ -3,4 +3,5 @@
 //! * Headers are not public
 //! * Manual pages: <https://www.ibm.com/docs/en/aix> (under "Technical reference" for that version)
 
+pub(crate) mod sys;
 pub(crate) mod unistd;

src/new/aix/sys/mod.rs

@@ -0,0 +1,3 @@
+//! Directory: `sys/`
+
+pub(crate) mod socket;

src/new/aix/sys/socket.rs

@@ -0,0 +1,9 @@
+//! Header: `sys/socket.h`
+
+pub use crate::new::common::posix::sys::socket::{
+    CMSG_DATA,
+    CMSG_FIRSTHDR,
+    CMSG_LEN,
+    CMSG_NXTHDR,
+    CMSG_SPACE,
+};

src/new/apple/libc/mod.rs

@@ -0,0 +1,7 @@
+//! Entrypoint for Apple headers, usually found as part of the Xcode SDK.
+//!
+//! <https://github.com/apple-oss-distributions/Libc/tree/main/include>
+
+pub(crate) mod signal;
+pub(crate) mod sys;
+pub(crate) mod unistd;

src/new/apple/libc/sys/mod.rs

@@ -0,0 +1,3 @@
+//! Directory: `sys/`
+
+pub(crate) mod socket;

src/new/apple/libc/sys/socket.rs

@@ -0,0 +1,20 @@
+//! Header: `sys/socket.h`
+//!
+//! <https://github.com/freebsd/freebsd-src/blob/main/sys/sys/socket.h>
+
+pub(crate) type __ALIGN_BOUNDARY = c_long;
+
+pub use crate::new::common::posix::sys::socket::{
+    CMSG_DATA,
+    CMSG_FIRSTHDR,
+    CMSG_LEN,
+    CMSG_SPACE,
+};
+
+pub unsafe fn CMSG_NXTHDR(mhdr: *const msghdr, cmsg: *const crate::cmsghdr) -> *mut crate::cmsghdr {
+    if cmsg.is_null() {
+        return CMSG_FIRSTHDR(mhdr);
+    }
+
+    crate::new::common::posix::sys::socket::CMSG_NXTHDR(mhdr, cmsg)
+}

src/new/apple/xnu/sys/mod.rs

@@ -3,6 +3,7 @@
 //! <https://github.com/apple-oss-distributions/xnu/tree/main/bsd/sys>
 
 pub(crate) mod signal;
+pub(crate) mod socket;
 
 /// Directory: `sys/_types`
 ///

src/new/apple/xnu/sys/socket.rs

@@ -0,0 +1,11 @@
+//! Header: `sys/socket.h`
+//!
+//! <https://github.com/apple-oss-distributions/xnu/blob/main/bsd/sys/socket.h>
+
+pub use crate::new::common::bsd::sys::socket::CMSG_NXTHDR;
+pub use crate::new::common::posix::sys::socket::{
+    CMSG_DATA,
+    CMSG_FIRSTHDR,
+    CMSG_LEN,
+    CMSG_SPACE,
+};