Gate statx syscall compat wrapper with feature flag (#501)

Signed-off-by: Alex Saveau <[email protected]>

Author: SUPERCILEX

Cargo.toml

@@ -194,3 +194,11 @@ os_pipe = ["io-lifetimes/os_pipe"]
 fs-err = ["io-lifetimes/fs-err"]
 #all-impls = ["async-std", "tokio", "os_pipe", "socket2", "mio", "fs-err"]
 all-impls = ["os_pipe", "fs-err"]
+
+# OS compatability features
+
+# Optimize for Linux 4.11 or later
+linux_4_11 = []
+
+# Enable all optimizations for the latest Linux versions.
+linux_latest = ["linux_4_11"]

src/fs/statx.rs

@@ -1,13 +1,16 @@
 //! Linux `statx`.
 
-use crate::fd::{AsFd, BorrowedFd};
-use crate::ffi::CStr;
+use crate::fd::AsFd;
 use crate::fs::AtFlags;
 use crate::{backend, io, path};
-use core::sync::atomic::{AtomicU8, Ordering};
 
 pub use backend::fs::types::{Statx, StatxFlags, StatxTimestamp};
 
+#[cfg(feature = "linux_4_11")]
+use backend::fs::syscalls::statx as _statx;
+#[cfg(not(feature = "linux_4_11"))]
+use compat::statx as _statx;
+
 /// `statx(dirfd, path, flags, mask, statxbuf)`
 ///
 /// This function returns [`io::Errno::NOSYS`] if `statx` is not available on
@@ -29,63 +32,74 @@ pub fn statx<P: path::Arg, Fd: AsFd>(
     path.into_with_c_str(|path| _statx(dirfd.as_fd(), path, flags, mask))
 }
 
-// Linux kernel prior to 4.11 old versions of Docker don't support `statx`. We
-// store the availability in a global to avoid unnecessary syscalls.
-//
-// 0: Unknown
-// 1: Not available
-// 2: Available
-static STATX_STATE: AtomicU8 = AtomicU8::new(0);
+#[cfg(not(feature = "linux_4_11"))]
+mod compat {
+    use crate::fd::BorrowedFd;
+    use crate::ffi::CStr;
+    use crate::fs::AtFlags;
+    use crate::{backend, io};
+    use core::sync::atomic::{AtomicU8, Ordering};
 
-#[inline]
-fn _statx(
-    dirfd: BorrowedFd<'_>,
-    path: &CStr,
-    flags: AtFlags,
-    mask: StatxFlags,
-) -> io::Result<Statx> {
-    match STATX_STATE.load(Ordering::Relaxed) {
-        0 => statx_init(dirfd, path, flags, mask),
-        1 => Err(io::Errno::NOSYS),
-        _ => backend::fs::syscalls::statx(dirfd, path, flags, mask),
+    use backend::fs::types::{Statx, StatxFlags};
+
+    // Linux kernel prior to 4.11 old versions of Docker don't support `statx`. We
+    // store the availability in a global to avoid unnecessary syscalls.
+    //
+    // 0: Unknown
+    // 1: Not available
+    // 2: Available
+    static STATX_STATE: AtomicU8 = AtomicU8::new(0);
+
+    #[inline]
+    pub fn statx(
+        dirfd: BorrowedFd<'_>,
+        path: &CStr,
+        flags: AtFlags,
+        mask: StatxFlags,
+    ) -> io::Result<Statx> {
+        match STATX_STATE.load(Ordering::Relaxed) {
+            0 => statx_init(dirfd, path, flags, mask),
+            1 => Err(io::Errno::NOSYS),
+            _ => backend::fs::syscalls::statx(dirfd, path, flags, mask),
+        }
     }
-}
 
-/// The first `statx` call. We don't know if `statx` is available yet.
-fn statx_init(
-    dirfd: BorrowedFd<'_>,
-    path: &CStr,
-    flags: AtFlags,
-    mask: StatxFlags,
-) -> io::Result<Statx> {
-    match backend::fs::syscalls::statx(dirfd, path, flags, mask) {
-        Err(io::Errno::NOSYS) => statx_error_nosys(),
-        Err(io::Errno::PERM) => statx_error_perm(),
-        result => {
-            STATX_STATE.store(2, Ordering::Relaxed);
-            result
+    /// The first `statx` call. We don't know if `statx` is available yet.
+    fn statx_init(
+        dirfd: BorrowedFd<'_>,
+        path: &CStr,
+        flags: AtFlags,
+        mask: StatxFlags,
+    ) -> io::Result<Statx> {
+        match backend::fs::syscalls::statx(dirfd, path, flags, mask) {
+            Err(io::Errno::NOSYS) => statx_error_nosys(),
+            Err(io::Errno::PERM) => statx_error_perm(),
+            result => {
+                STATX_STATE.store(2, Ordering::Relaxed);
+                result
+            }
         }
     }
-}
 
-/// The first `statx` call failed with `NOSYS` (or something we're treating
-/// like `NOSYS`).
-#[cold]
-fn statx_error_nosys() -> io::Result<Statx> {
-    STATX_STATE.store(1, Ordering::Relaxed);
-    Err(io::Errno::NOSYS)
-}
+    /// The first `statx` call failed with `NOSYS` (or something we're treating
+    /// like `NOSYS`).
+    #[cold]
+    fn statx_error_nosys() -> io::Result<Statx> {
+        STATX_STATE.store(1, Ordering::Relaxed);
+        Err(io::Errno::NOSYS)
+    }
 
-/// The first `statx` call failed with `PERM`.
-#[cold]
-fn statx_error_perm() -> io::Result<Statx> {
-    // Some old versions of Docker have `statx` fail with `PERM` when it isn't
-    // recognized. Check whether `statx` really is available, and if so, fail
-    // with `PERM`, and if not, treat it like `NOSYS`.
-    if backend::fs::syscalls::is_statx_available() {
-        STATX_STATE.store(2, Ordering::Relaxed);
-        Err(io::Errno::PERM)
-    } else {
-        statx_error_nosys()
+    /// The first `statx` call failed with `PERM`.
+    #[cold]
+    fn statx_error_perm() -> io::Result<Statx> {
+        // Some old versions of Docker have `statx` fail with `PERM` when it isn't
+        // recognized. Check whether `statx` really is available, and if so, fail
+        // with `PERM`, and if not, treat it like `NOSYS`.
+        if backend::fs::syscalls::is_statx_available() {
+            STATX_STATE.store(2, Ordering::Relaxed);
+            Err(io::Errno::PERM)
+        } else {
+            statx_error_nosys()
+        }
     }
 }