glibc: Initial setup of source reorganization

Establish the basic source reorganization for glibc, and seed it with a
`net/route.h` definition.

Glibc has the same headers in various locations, then copies or (I
believe) combines them in the install location based on the target
platform. To mirror this, our source primarily mirrors the glibc source
tree, then reexports things in `src/new/glibc.rs` in the same way that
glibc does when it creates an install.

(backport <#4540>)
(cherry picked from commit 0399c4e)

Author: tgross35

src/new/glibc/mod.rs

@@ -2,5 +2,24 @@
 //!
 //! * Headers: <https://sourceware.org/git/?p=glibc.git> (official)
 //! * Headers: <https://github.com/bminor/glibc> (mirror)
+//!
+//! This module structure is modeled after glibc's source tree. Its build system selects headers
+//! from different locations based on the platform, which we mimic here with reexports.
+
+/// Source directory: `posix/`
+///
+/// <https://github.com/bminor/glibc/tree/master/posix>
+mod posix {
+    pub(crate) mod unistd;
+}
+
+/// Source directory: `sysdeps/`
+///
+/// <https://github.com/bminor/glibc/tree/master/sysdeps>
+mod sysdeps {
+    pub(crate) mod unix;
+}
 
-pub(crate) mod unistd;
+pub(crate) use posix::*;
+#[cfg(target_os = "linux")]
+pub(crate) use sysdeps::unix::linux::*;

src/new/glibc/unistd.rs renamed to src/new/glibc/posix/unistd.rs

@@ -1,4 +1,6 @@
 //! Header: `unistd.h`
+//!
+//! <https://github.com/bminor/glibc/blob/master/posix/unistd.h>
 
 pub use crate::new::common::posix::unistd::{
     STDERR_FILENO,

src/new/glibc/sysdeps/unix/linux/mod.rs

@@ -0,0 +1,10 @@
+//! Source directory: `sysdeps/unix/sysv/linux` (the `sysv` is flattened).
+//!
+//! <https://github.com/bminor/glibc/tree/master/sysdeps/unix/sysv/linux>
+
+/// Directory: `net/`
+///
+/// Source directory: `sysdeps/unix/sysv/linux/net`
+pub(crate) mod net {
+    pub(crate) mod route;
+}

src/new/glibc/sysdeps/unix/linux/net/route.rs

@@ -0,0 +1,30 @@
+//! Header: `net/route.h`
+//!
+//! Source header: `sysdeps/unix/sysv/linux/net/route.h`
+//! <https://github.com/bminor/glibc/blob/master/sysdeps/unix/sysv/linux/net/route.h>
+
+use crate::prelude::*;
+
+s! {
+    pub struct rtentry {
+        pub rt_pad1: c_ulong,
+        pub rt_dst: crate::sockaddr,
+        pub rt_gateway: crate::sockaddr,
+        pub rt_genmask: crate::sockaddr,
+        pub rt_flags: c_ushort,
+        pub rt_pad2: c_short,
+        pub rt_pad3: c_ulong,
+        pub rt_tos: c_uchar,
+        pub rt_class: c_uchar,
+        // FIXME(1.0): private padding fields
+        #[cfg(target_pointer_width = "64")]
+        pub rt_pad4: [c_short; 3usize],
+        #[cfg(not(target_pointer_width = "64"))]
+        pub rt_pad4: c_short,
+        pub rt_metric: c_short,
+        pub rt_dev: *mut c_char,
+        pub rt_mtu: c_ulong,
+        pub rt_window: c_ulong,
+        pub rt_irtt: c_ushort,
+    }
+}

src/new/glibc/sysdeps/unix/mod.rs

@@ -0,0 +1,6 @@
+//! Source directory: `sysdeps/unix/`
+//!
+//! <https://github.com/bminor/glibc/tree/master/sysdeps/unix>
+
+#[cfg(target_os = "linux")]
+pub(crate) mod linux;

src/new/mod.rs

@@ -177,6 +177,8 @@ cfg_if! {
         pub use linux::can::raw::*;
         pub use linux::can::*;
         pub use linux::keyctl::*;
+        #[cfg(target_env = "gnu")]
+        pub use net::route::*;
     } else if #[cfg(target_vendor = "apple")] {
         pub use signal::*;
     }

src/unix/linux_like/linux/gnu/mod.rs

@@ -153,27 +153,6 @@ s! {
         pub nm_gid: u32,
     }
 
-    pub struct rtentry {
-        pub rt_pad1: c_ulong,
-        pub rt_dst: crate::sockaddr,
-        pub rt_gateway: crate::sockaddr,
-        pub rt_genmask: crate::sockaddr,
-        pub rt_flags: c_ushort,
-        pub rt_pad2: c_short,
-        pub rt_pad3: c_ulong,
-        pub rt_tos: c_uchar,
-        pub rt_class: c_uchar,
-        #[cfg(target_pointer_width = "64")]
-        pub rt_pad4: [c_short; 3usize],
-        #[cfg(not(target_pointer_width = "64"))]
-        pub rt_pad4: c_short,
-        pub rt_metric: c_short,
-        pub rt_dev: *mut c_char,
-        pub rt_mtu: c_ulong,
-        pub rt_window: c_ulong,
-        pub rt_irtt: c_ushort,
-    }
-
     pub struct ntptimeval {
         pub time: crate::timeval,
         pub maxerror: c_long,