Remove procfs. (#1275)

Remove the procfs module, as most users don't need this functionality
and it can be implemented as a layer on top of rustix. This layer is now
available in the [rustix-linux-procfs] crate.

This requires changing `ttyname` to not use the `procfs` crate. It now
just uses a hard-coded "/proc/self/fd" path.

[rustix-linux-procfs]: https://crates.io/crates/rustix-linux-procfs

Cargo.toml

@@ -23,11 +23,6 @@ core = { version = "1.0.0", optional = true, package = "rustc-std-workspace-core
 rustc-std-workspace-alloc = { version = "1.0.0", optional = true } # not aliased here but in lib.rs because of name collision with the alloc feature
 compiler_builtins = { version = '0.1.49', optional = true }
 
-# The procfs feature needs once_cell.
-# With Rust 1.70.0, we can switch to `core::cell::OnceCell`.
-[target.'cfg(any(target_os = "android", target_os = "linux"))'.dependencies]
-once_cell = { version = "1.5.2", optional = true }
-
 # Dependencies for platforms where linux_raw is supported, in addition to libc:
 #
 # On Linux on selected architectures, the linux_raw backend is supported, in
@@ -151,10 +146,7 @@ shm = ["fs"]
 time = []
 
 # Enable `rustix::param::*`.
-param = ["fs"]
-
-# Enable this to enable `rustix::io::proc_self_*` (on Linux) and `ttyname`.
-procfs = ["once_cell", "fs"]
+param = []
 
 # Enable `rustix::pty::*`.
 pty = ["fs"]
@@ -192,7 +184,6 @@ all-apis = [
     "param",
     "pipe",
     "process",
-    "procfs",
     "pty",
     "rand",
     "runtime",

README.md

@@ -66,7 +66,6 @@ default. The rest of the API is conditional with cargo feature flags:
 | `param`    | [`rustix::param`]—Process parameters.                          |
 | `pipe`     | [`rustix::pipe`]—Pipe operations.                              |
 | `process`  | [`rustix::process`]—Process-associated operations.             |
-| `procfs`   | [`rustix::procfs`]—Utilities for reading `/proc` on Linux.     |
 | `pty`      | [`rustix::pty`]—Pseudoterminal operations.                     |
 | `rand`     | [`rustix::rand`]—Random-related operations.                    |
 | `shm`      | [`rustix::shm`]—POSIX shared memory.                           |
@@ -87,7 +86,6 @@ default. The rest of the API is conditional with cargo feature flags:
 [`rustix::param`]: https://docs.rs/rustix/*/rustix/param/index.html
 [`rustix::pipe`]: https://docs.rs/rustix/*/rustix/pipe/index.html
 [`rustix::process`]: https://docs.rs/rustix/*/rustix/process/index.html
-[`rustix::procfs`]: https://docs.rs/rustix/*/rustix/procfs/index.html
 [`rustix::pty`]: https://docs.rs/rustix/*/rustix/pty/index.html
 [`rustix::rand`]: https://docs.rs/rustix/*/rustix/rand/index.html
 [`rustix::shm`]: https://docs.rs/rustix/*/rustix/shm/index.html

examples/stdio.rs

@@ -7,7 +7,6 @@ use rustix::termios::isatty;
 #[cfg(all(
     not(any(windows, target_os = "fuchsia")),
     feature = "termios",
-    feature = "procfs",
     feature = "alloc"
 ))]
 use rustix::termios::ttyname;
@@ -62,7 +61,7 @@ fn show<Fd: AsFd>(fd: Fd) -> io::Result<()> {
 
     #[cfg(feature = "termios")]
     if isatty(fd) {
-        #[cfg(all(feature = "alloc", feature = "procfs"))]
+        #[cfg(feature = "alloc")]
         #[cfg(not(target_os = "fuchsia"))]
         println!(" - ttyname: {}", ttyname(fd, Vec::new())?.to_string_lossy());
 

src/backend/libc/fs/syscalls.rs

@@ -1,11 +1,7 @@
 //! libc syscalls supporting `rustix::fs`.
 
 use crate::backend::c;
-#[cfg(any(
-    not(target_os = "redox"),
-    feature = "alloc",
-    all(linux_kernel, feature = "procfs")
-))]
+#[cfg(any(not(target_os = "redox"), feature = "alloc"))]
 use crate::backend::conv::ret_usize;
 use crate::backend::conv::{borrowed_fd, c_str, ret, ret_c_int, ret_off_t, ret_owned_fd};
 use crate::fd::{BorrowedFd, OwnedFd};

src/backend/libc/mod.rs

@@ -175,7 +175,7 @@ pub(crate) fn if_glibc_is_less_than_2_25() -> bool {
 }
 
 // Private modules used by multiple public modules.
-#[cfg(any(feature = "procfs", feature = "process", feature = "runtime"))]
+#[cfg(any(feature = "process", feature = "runtime"))]
 #[cfg(not(any(windows, target_os = "wasi")))]
 pub(crate) mod pid;
 #[cfg(any(feature = "process", feature = "thread"))]

src/backend/libc/termios/syscalls.rs

@@ -9,15 +9,12 @@ use crate::backend::c;
 use crate::backend::conv::ret_pid_t;
 use crate::backend::conv::{borrowed_fd, ret};
 use crate::fd::BorrowedFd;
-#[cfg(all(feature = "alloc", feature = "procfs"))]
+#[cfg(feature = "alloc")]
 #[cfg(not(any(target_os = "fuchsia", target_os = "wasi")))]
 use crate::ffi::CStr;
 #[cfg(any(
     not(target_os = "espidf"),
-    all(
-        feature = "procfs",
-        not(any(target_os = "fuchsia", target_os = "wasi"))
-    )
+    not(any(target_os = "fuchsia", target_os = "wasi"))
 ))]
 use core::mem::MaybeUninit;
 #[cfg(not(target_os = "wasi"))]
@@ -508,7 +505,7 @@ pub(crate) fn isatty(fd: BorrowedFd<'_>) -> bool {
     unsafe { c::isatty(borrowed_fd(fd)) != 0 }
 }
 
-#[cfg(all(feature = "alloc", feature = "procfs"))]
+#[cfg(feature = "alloc")]
 #[cfg(not(any(target_os = "fuchsia", target_os = "wasi")))]
 pub(crate) fn ttyname(dirfd: BorrowedFd<'_>, buf: &mut [MaybeUninit<u8>]) -> io::Result<usize> {
     unsafe {

src/backend/linux_raw/mod.rs

@@ -89,7 +89,7 @@ pub(crate) mod fd {
 pub(crate) mod c;
 
 // Private modules used by multiple public modules.
-#[cfg(any(feature = "procfs", feature = "process", feature = "runtime"))]
+#[cfg(any(feature = "process", feature = "runtime"))]
 pub(crate) mod pid;
 #[cfg(any(feature = "process", feature = "thread"))]
 pub(crate) mod prctl;

src/backend/linux_raw/termios/syscalls.rs

@@ -10,13 +10,11 @@ use crate::backend::conv::{by_ref, c_uint, ret};
 use crate::fd::BorrowedFd;
 use crate::io;
 use crate::pid::Pid;
-#[cfg(all(feature = "alloc", feature = "procfs"))]
-use crate::procfs;
 use crate::termios::{
     speed, Action, ControlModes, InputModes, LocalModes, OptionalActions, OutputModes,
     QueueSelector, SpecialCodeIndex, Termios, Winsize,
 };
-#[cfg(all(feature = "alloc", feature = "procfs"))]
+#[cfg(feature = "alloc")]
 use crate::{ffi::CStr, fs::FileType, path::DecInt};
 use core::mem::MaybeUninit;
 
@@ -366,7 +364,7 @@ pub(crate) fn isatty(fd: BorrowedFd<'_>) -> bool {
     tcgetwinsize(fd).is_ok()
 }
 
-#[cfg(all(feature = "alloc", feature = "procfs"))]
+#[cfg(feature = "alloc")]
 pub(crate) fn ttyname(fd: BorrowedFd<'_>, buf: &mut [MaybeUninit<u8>]) -> io::Result<usize> {
     let fd_stat = crate::backend::fs::syscalls::fstat(fd)?;
 
@@ -378,15 +376,18 @@ pub(crate) fn ttyname(fd: BorrowedFd<'_>, buf: &mut [MaybeUninit<u8>]) -> io::Re
     // Check that `fd` is really a tty.
     tcgetwinsize(fd)?;
 
-    // Get a fd to "/proc/self/fd".
-    let proc_self_fd = procfs::proc_self_fd()?;
+    // Create the "/proc/self/fd/<fd>" string.
+    let mut proc_self_fd_buf: [u8; 25] = *b"/proc/self/fd/\0\0\0\0\0\0\0\0\0\0\0";
+    let dec_int = DecInt::from_fd(fd);
+    let bytes_with_nul = dec_int.as_bytes_with_nul();
+    proc_self_fd_buf[b"/proc/self/fd/".len()..][..bytes_with_nul.len()]
+        .copy_from_slice(bytes_with_nul);
+
+    // SAFETY: We just wrote a valid C String.
+    let proc_self_fd_path = unsafe { CStr::from_ptr(proc_self_fd_buf.as_ptr().cast()) };
 
     // Gather the ttyname by reading the "fd" file inside `proc_self_fd`.
-    let r = crate::backend::fs::syscalls::readlinkat(
-        proc_self_fd,
-        DecInt::from_fd(fd).as_c_str(),
-        buf,
-    )?;
+    let r = crate::backend::fs::syscalls::readlinkat(crate::fs::CWD, proc_self_fd_path, buf)?;
 
     // If the number of bytes is equal to the buffer length, truncation may
     // have occurred. This check also ensures that we have enough space for

src/lib.rs

@@ -252,10 +252,6 @@ pub mod pipe;
 #[cfg(feature = "process")]
 #[cfg_attr(docsrs, doc(cfg(feature = "process")))]
 pub mod process;
-#[cfg(feature = "procfs")]
-#[cfg(linux_kernel)]
-#[cfg_attr(docsrs, doc(cfg(feature = "procfs")))]
-pub mod procfs;
 #[cfg(not(windows))]
 #[cfg(not(target_os = "wasi"))]
 #[cfg(feature = "pty")]
@@ -346,7 +342,6 @@ pub(crate) mod path;
 mod clockid;
 #[cfg(not(any(windows, target_os = "wasi")))]
 #[cfg(any(
-    feature = "procfs",
     feature = "process",
     feature = "runtime",
     feature = "termios",