add some descriptions for items in the poll header

src/header/poll/mod.rs

@@ -22,24 +22,42 @@ use crate::{
     },
 };
 
+/// Data other than high-priority data may be read without blocking.
 pub const POLLIN: c_short = 0x001;
+/// High-priority data may be read without blocking.
 pub const POLLPRI: c_short = 0x002;
+/// Normal data may be written without blocking.
 pub const POLLOUT: c_short = 0x004;
+/// An error has occurred (revents only).
 pub const POLLERR: c_short = 0x008;
+/// Device has been disconnected (revents only).
 pub const POLLHUP: c_short = 0x010;
+/// Invalid fd member (revents only).
 pub const POLLNVAL: c_short = 0x020;
+/// Normal data may be read without blocking.
 pub const POLLRDNORM: c_short = 0x040;
+/// Priority data may be read without blocking.
 pub const POLLRDBAND: c_short = 0x080;
+/// Equivalent to POLLOUT.
 pub const POLLWRNORM: c_short = 0x100;
+/// Priority data may be written.
 pub const POLLWRBAND: c_short = 0x200;
 
+/// An unsigned integer type used for the number of file descriptors.
+#[allow(non_camel_case_types)]
 pub type nfds_t = c_ulong;
 
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/poll.h.html>.
+///
+/// A structure storing a file descriptor along with input and output flags for poll operations.
+#[allow(non_camel_case_types)]
 #[repr(C)]
 pub struct pollfd {
+    /// The following descriptor being polled.
     pub fd: c_int,
+    /// The input event flags.
     pub events: c_short,
+    /// The output event flags.
     pub revents: c_short,
 }
 
@@ -139,6 +157,15 @@ pub unsafe fn poll_epoll(fds: &mut [pollfd], timeout: c_int, sigmask: *const sig
 }
 
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/poll.html>.
+///
+/// Provides applications with a mechanism for multiplexing input/output
+/// over a set of file descriptors.
+///
+/// - The `timeout` parameter represents milliseconds.
+/// - A `timeout` of `-1` is equivalent to passing a null pointer for `tmo_p` to `ppoll`.
+/// - `poll` should behave equivalent to `ppoll` with a null pointer for `sigmask`.
+///
+/// Note: Uses epoll internally.
 #[unsafe(no_mangle)]
 pub unsafe extern "C" fn poll(fds: *mut pollfd, nfds: nfds_t, timeout: c_int) -> c_int {
     trace_expr!(
@@ -157,6 +184,14 @@ pub unsafe extern "C" fn poll(fds: *mut pollfd, nfds: nfds_t, timeout: c_int) ->
 }
 
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/ppoll.html>.
+///
+/// Provides applications with a mechanism for multiplexing input/output
+/// over a set of file descriptors.
+///
+/// - The `tmo_p` parameter is the timeout as represented by a `timespec` struct.
+/// - Passing a null pointer for timeout is equivalent to `-1` for `timeout` to `poll`.
+///
+/// Note: Uses epoll internally.
 #[unsafe(no_mangle)]
 pub unsafe extern "C" fn ppoll(
     fds: *mut pollfd,