[RFC][wip] rustix: on Linux, support a build without linux-raw-sys

Rustix support was added to Mesa3D recently, but it only works
with the linux-raw-sys backend.  On Linux, even the libc
backend, there is a dependency on linux-raw-sys for certain ABI
definitions.

When updating rustix in Android to support this, I realized only
the libc backend is supported in Android.  This is because
Android as a platform wants to discourage raw syscalls, and to
be able to globally update libc.

Features like fdtrack would not work with the linux-raw-sys backend:

https://android.googlesource.com/platform/bionic/+/HEAD/docs/fdtrack.md

Given Android wants to incentize use of libc only, this MR introduces
the concept of "linux-raw-dep".  This means that linux-raw-sys is
present as a dependency for the user.  This will be on by default
even for the libc backend, but will be turned off for Android.

This will also help others who don't need all the features rustix
offers on Linux, so they have one less dependency to maintain.

Tested via:

cargo build --features=use-libc,net,std,alloc,event,fs,mm,param,pipe

These are the same set of features needed by Mesa3D.

Author: gsingh408

Cargo.toml

@@ -259,6 +259,7 @@ check-cfg = [
     'cfg(linux_kernel)',
     'cfg(linux_like)',
     'cfg(linux_raw)',
+    'cfg(linux_raw_dep)',
     'cfg(lower_upper_exp_for_non_zero)',
     'cfg(netbsdlike)',
     'cfg(rustc_attrs)',

src/backend/libc/c.rs

@@ -19,49 +19,49 @@ pub(crate) const NFS_SUPER_MAGIC: u32 = 0x0000_6969;
 pub(crate) const EXIT_SIGNALED_SIGABRT: c_int = 128 + SIGABRT as c_int;
 
 // TODO: Upstream these.
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_TSN: c_int = linux_raw_sys::if_ether::ETH_P_TSN as _;
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_ERSPAN2: c_int = linux_raw_sys::if_ether::ETH_P_ERSPAN2 as _;
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_ERSPAN: c_int = linux_raw_sys::if_ether::ETH_P_ERSPAN as _;
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_PROFINET: c_int = linux_raw_sys::if_ether::ETH_P_PROFINET as _;
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_REALTEK: c_int = linux_raw_sys::if_ether::ETH_P_REALTEK as _;
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_ETHERCAT: c_int = linux_raw_sys::if_ether::ETH_P_ETHERCAT as _;
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_PREAUTH: c_int = linux_raw_sys::if_ether::ETH_P_PREAUTH as _;
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_LLDP: c_int = linux_raw_sys::if_ether::ETH_P_LLDP as _;
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_MRP: c_int = linux_raw_sys::if_ether::ETH_P_MRP as _;
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_NCSI: c_int = linux_raw_sys::if_ether::ETH_P_NCSI as _;
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_CFM: c_int = linux_raw_sys::if_ether::ETH_P_CFM as _;
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_IBOE: c_int = linux_raw_sys::if_ether::ETH_P_IBOE as _;
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_HSR: c_int = linux_raw_sys::if_ether::ETH_P_HSR as _;
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_NSH: c_int = linux_raw_sys::if_ether::ETH_P_NSH as _;
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_DSA_8021Q: c_int = linux_raw_sys::if_ether::ETH_P_DSA_8021Q as _;
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_DSA_A5PSW: c_int = linux_raw_sys::if_ether::ETH_P_DSA_A5PSW as _;
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_IFE: c_int = linux_raw_sys::if_ether::ETH_P_IFE as _;
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_CAN: c_int = linux_raw_sys::if_ether::ETH_P_CAN as _;
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_CANXL: c_int = linux_raw_sys::if_ether::ETH_P_CANXL as _;
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_XDSA: c_int = linux_raw_sys::if_ether::ETH_P_XDSA as _;
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_MAP: c_int = linux_raw_sys::if_ether::ETH_P_MAP as _;
-#[cfg(all(linux_kernel, feature = "net"))]
+#[cfg(all(linux_raw_dep, feature = "net"))]
 pub(crate) const ETH_P_MCTP: c_int = linux_raw_sys::if_ether::ETH_P_MCTP as _;
 
 #[cfg(all(
@@ -90,7 +90,7 @@ pub(crate) const MSG_DONTWAIT: c_int = MSG_NONBLOCK;
 // <https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/open.c?h=v6.13#n1423>
 // so libc implementations may leave it undefined or defined to zero.
 #[cfg(linux_kernel)]
-pub(crate) const O_LARGEFILE: c_int = linux_raw_sys::general::O_LARGEFILE as _;
+pub(crate) const O_LARGEFILE: c_int = libc::O_LARGEFILE as _;
 
 // Gated under `_LARGEFILE_SOURCE` but automatically set by the kernel.
 // <https://github.com/illumos/illumos-gate/blob/fb2cb638e5604b214d8ea8d4f01ad2e77b437c17/usr/src/ucbhead/sys/fcntl.h#L64>

src/backend/libc/fs/mod.rs

@@ -16,9 +16,9 @@ pub(crate) mod syscalls;
 pub(crate) mod types;
 
 // TODO: Fix linux-raw-sys to define ioctl codes for sparc.
-#[cfg(all(linux_kernel, any(target_arch = "sparc", target_arch = "sparc64")))]
+#[cfg(all(linux_raw_dep, any(target_arch = "sparc", target_arch = "sparc64")))]
 pub(crate) const EXT4_IOC_RESIZE_FS: crate::ioctl::Opcode = 0x8008_6610;
 
-#[cfg(all(linux_kernel, not(any(target_arch = "sparc", target_arch = "sparc64"))))]
+#[cfg(all(linux_raw_dep, not(any(target_arch = "sparc", target_arch = "sparc64"))))]
 pub(crate) const EXT4_IOC_RESIZE_FS: crate::ioctl::Opcode =
     linux_raw_sys::ioctl::EXT4_IOC_RESIZE_FS as crate::ioctl::Opcode;

src/backend/libc/fs/syscalls.rs

@@ -1840,7 +1840,7 @@ pub(crate) fn memfd_create(name: &CStr, flags: MemfdFlags) -> io::Result<OwnedFd
     unsafe { ret_owned_fd(memfd_create(c_str(name), bitflags_bits!(flags))) }
 }
 
-#[cfg(linux_kernel)]
+#[cfg(linux_raw_dep)]
 pub(crate) fn openat2(
     dirfd: BorrowedFd<'_>,
     path: &CStr,

src/backend/libc/io/types.rs

@@ -27,15 +27,15 @@ bitflags! {
     #[derive(Copy, Clone, Eq, PartialEq, Hash, Debug)]
     pub struct ReadWriteFlags: u32 {
         /// `RWF_DSYNC` (since Linux 4.7)
-        const DSYNC = linux_raw_sys::general::RWF_DSYNC;
+        const DSYNC = libc::RWF_DSYNC as u32;
         /// `RWF_HIPRI` (since Linux 4.6)
-        const HIPRI = linux_raw_sys::general::RWF_HIPRI;
+        const HIPRI = libc::RWF_HIPRI as u32;
         /// `RWF_SYNC` (since Linux 4.7)
-        const SYNC = linux_raw_sys::general::RWF_SYNC;
+        const SYNC = libc::RWF_SYNC as u32;
         /// `RWF_NOWAIT` (since Linux 4.14)
-        const NOWAIT = linux_raw_sys::general::RWF_NOWAIT;
+        const NOWAIT = libc::RWF_NOWAIT as u32;
         /// `RWF_APPEND` (since Linux 4.16)
-        const APPEND = linux_raw_sys::general::RWF_APPEND;
+        const APPEND = libc::RWF_APPEND as u32;
 
         /// <https://docs.rs/bitflags/*/bitflags/#externally-defined-flags>
         const _ = !0;

src/backend/libc/mm/types.rs

@@ -44,19 +44,19 @@ bitflags! {
         #[cfg(linux_kernel)]
         const GROWSDOWN = bitcast!(c::PROT_GROWSDOWN);
         /// `PROT_SEM`
-        #[cfg(linux_kernel)]
+        #[cfg(linux_raw_dep)]
         const SEM = linux_raw_sys::general::PROT_SEM;
         /// `PROT_BTI`
-        #[cfg(all(linux_kernel, target_arch = "aarch64"))]
+        #[cfg(all(linux_raw_dep, target_arch = "aarch64"))]
         const BTI = linux_raw_sys::general::PROT_BTI;
         /// `PROT_MTE`
-        #[cfg(all(linux_kernel, target_arch = "aarch64"))]
+        #[cfg(all(linux_raw_dep, target_arch = "aarch64"))]
         const MTE = linux_raw_sys::general::PROT_MTE;
         /// `PROT_SAO`
-        #[cfg(all(linux_kernel, any(target_arch = "powerpc", target_arch = "powerpc64")))]
+        #[cfg(all(linux_raw_dep, any(target_arch = "powerpc", target_arch = "powerpc64")))]
         const SAO = linux_raw_sys::general::PROT_SAO;
         /// `PROT_ADI`
-        #[cfg(all(linux_kernel, any(target_arch = "sparc", target_arch = "sparc64")))]
+        #[cfg(all(linux_raw_dep, any(target_arch = "sparc", target_arch = "sparc64")))]
         const ADI = linux_raw_sys::general::PROT_ADI;
 
         /// <https://docs.rs/bitflags/*/bitflags/#externally-defined-flags>

src/backend/libc/net/sockopt.rs

@@ -76,7 +76,7 @@ use c::TCP_KEEPALIVE as TCP_KEEPIDLE;
 use c::TCP_KEEPIDLE;
 use core::mem::{size_of, MaybeUninit};
 use core::time::Duration;
-#[cfg(target_os = "linux")]
+#[cfg(linux_raw_dep)]
 use linux_raw_sys::xdp::{xdp_mmap_offsets, xdp_statistics, xdp_statistics_v1};
 #[cfg(windows)]
 use windows_sys::Win32::Foundation::BOOL;
@@ -1090,7 +1090,7 @@ pub(crate) fn set_xdp_rx_ring_size(fd: BorrowedFd<'_>, value: u32) -> io::Result
     setsockopt(fd, c::SOL_XDP, c::XDP_RX_RING, value)
 }
 
-#[cfg(target_os = "linux")]
+#[cfg(linux_raw_dep)]
 #[inline]
 pub(crate) fn xdp_mmap_offsets(fd: BorrowedFd<'_>) -> io::Result<XdpMmapOffsets> {
     // The kernel will write `xdp_mmap_offsets` or `xdp_mmap_offsets_v1` to the
@@ -1177,7 +1177,7 @@ pub(crate) fn xdp_mmap_offsets(fd: BorrowedFd<'_>) -> io::Result<XdpMmapOffsets>
     }
 }
 
-#[cfg(target_os = "linux")]
+#[cfg(linux_raw_dep)]
 #[inline]
 pub(crate) fn xdp_statistics(fd: BorrowedFd<'_>) -> io::Result<XdpStatistics> {
     let mut optlen = size_of::<xdp_statistics>().try_into().unwrap();

src/fs/ioctl.rs

@@ -58,7 +58,7 @@ pub fn ioctl_ficlone<Fd: AsFd, SrcFd: AsFd>(fd: Fd, src_fd: SrcFd) -> io::Result
 }
 
 /// `ioctl(fd, EXT4_IOC_RESIZE_FS, blocks)`—Resize ext4 filesystem on fd.
-#[cfg(linux_kernel)]
+#[cfg(linux_raw_dep)]
 #[inline]
 #[doc(alias = "EXT4_IOC_RESIZE_FS")]
 pub fn ext4_ioc_resize_fs<Fd: AsFd>(fd: Fd, blocks: u64) -> io::Result<()> {
@@ -94,7 +94,7 @@ unsafe impl ioctl::Ioctl for Ficlone<'_> {
     }
 }
 
-#[cfg(linux_kernel)]
+#[cfg(linux_raw_dep)]
 bitflags! {
     /// `FS_*` constants for use with [`ioctl_getflags`].
     ///
@@ -136,7 +136,7 @@ bitflags! {
 /// `ioctl(fd, FS_IOC_GETFLAGS)`—Returns the [inode flags] attributes
 ///
 /// [inode flags]: https://man7.org/linux/man-pages/man2/ioctl_iflags.2.html
-#[cfg(linux_kernel)]
+#[cfg(linux_raw_dep)]
 #[inline]
 #[doc(alias = "FS_IOC_GETFLAGS")]
 pub fn ioctl_getflags<Fd: AsFd>(fd: Fd) -> io::Result<IFlags> {
@@ -153,7 +153,7 @@ pub fn ioctl_getflags<Fd: AsFd>(fd: Fd) -> io::Result<IFlags> {
 /// `ioctl(fd, FS_IOC_SETFLAGS)`—Modify the [inode flags] attributes
 ///
 /// [inode flags]: https://man7.org/linux/man-pages/man2/ioctl_iflags.2.html
-#[cfg(linux_kernel)]
+#[cfg(linux_raw_dep)]
 #[inline]
 #[doc(alias = "FS_IOC_SETFLAGS")]
 pub fn ioctl_setflags<Fd: AsFd>(fd: Fd, flags: IFlags) -> io::Result<()> {

src/fs/mod.rs

@@ -30,7 +30,7 @@ pub(crate) mod fd;
 mod getpath;
 #[cfg(not(target_os = "wasi"))] // WASI doesn't have get[gpu]id.
 mod id;
-#[cfg(linux_kernel)]
+#[cfg(linux_raw_dep)]
 pub mod inotify;
 #[cfg(linux_kernel)]
 mod ioctl;
@@ -45,7 +45,7 @@ mod ioctl;
 mod makedev;
 #[cfg(any(linux_kernel, target_os = "freebsd"))]
 mod memfd_create;
-#[cfg(linux_kernel)]
+#[cfg(linux_raw_dep)]
 mod openat2;
 #[cfg(linux_kernel)]
 mod raw_dir;
@@ -110,7 +110,7 @@ pub use ioctl::*;
 pub use makedev::*;
 #[cfg(any(linux_kernel, target_os = "freebsd"))]
 pub use memfd_create::memfd_create;
-#[cfg(linux_kernel)]
+#[cfg(linux_raw_dep)]
 pub use openat2::openat2;
 #[cfg(linux_kernel)]
 pub use raw_dir::{RawDir, RawDirEntry};

src/fs/raw_dir.rs

@@ -7,6 +7,10 @@ use crate::fs::FileType;
 use crate::io;
 use core::fmt;
 use core::mem::{align_of, MaybeUninit};
+
+#[cfg(not(linux_raw_dep))]
+use libc::dirent64 as linux_dirent64;
+#[cfg(linux_raw_dep)]
 use linux_raw_sys::general::linux_dirent64;
 
 /// A directory iterator implemented with getdents.