Add shm_open/shm_unlink (POSIX shared memory)

Fixes #705.

Cargo.toml

@@ -149,6 +149,9 @@ thread = ["linux-raw-sys/prctl"]
 # Enable `rustix::process::*`.
 process = ["linux-raw-sys/prctl"]
 
+# Enable `rustix::shm::*`.
+shm = []
+
 # Enable `rustix::time::*`.
 time = []
 

src/backend/libc/conv.rs

@@ -91,7 +91,7 @@ pub(super) fn ret_usize(raw: c::ssize_t) -> io::Result<usize> {
 }
 
 #[cfg(not(windows))]
-#[cfg(feature = "fs")]
+#[cfg(any(feature = "fs", feature = "shm"))]
 #[inline]
 pub(super) fn ret_off_t(raw: c::off_t) -> io::Result<c::off_t> {
     if raw == -1 {

src/backend/libc/mod.rs

@@ -105,7 +105,7 @@ pub(crate) mod c;
 #[cfg(feature = "event")]
 pub(crate) mod event;
 #[cfg(not(windows))]
-#[cfg(feature = "fs")]
+#[cfg(any(feature = "fs", feature = "shm"))]
 pub(crate) mod fs;
 pub(crate) mod io;
 #[cfg(linux_kernel)]
@@ -184,6 +184,8 @@ pub(crate) mod pid;
 #[cfg(any(feature = "process", feature = "thread"))]
 #[cfg(linux_kernel)]
 pub(crate) mod prctl;
+#[cfg(feature = "shm")]
+pub(crate) mod shm;
 #[cfg(any(feature = "fs", feature = "thread", feature = "process"))]
 #[cfg(not(any(windows, target_os = "wasi")))]
 pub(crate) mod ugid;

src/backend/libc/shm/mod.rs

@@ -0,0 +1 @@
+pub(crate) mod syscalls;

src/backend/libc/shm/syscalls.rs

@@ -0,0 +1,28 @@
+use std::ffi::CStr;
+
+use crate::backend::c;
+use crate::backend::conv::{c_str, ret, ret_owned_fd};
+use crate::fd::OwnedFd;
+use crate::fs::{Mode, OFlags};
+use crate::io;
+
+#[cfg(not(any(target_os = "android", target_os = "espidf", target_os = "wasi")))]
+pub(crate) fn shm_open(name: &CStr, oflags: OFlags, mode: Mode) -> io::Result<OwnedFd> {
+    // On this platforms, `mode_t` is `u16` and can't be passed directly to a
+    // variadic function.
+    #[cfg(apple)]
+    let mode: c::c_uint = mode.bits().into();
+
+    // Otherwise, cast to `mode_t` as that's what `open` is documented to take.
+    #[cfg(not(apple))]
+    let mode: c::mode_t = mode.bits() as _;
+
+    unsafe { ret_owned_fd(c::shm_open(c_str(name), bitflags_bits!(oflags), mode)) }
+}
+
+#[cfg(not(any(target_os = "android", target_os = "espidf", target_os = "wasi")))]
+pub(crate) fn shm_unlink(name: &CStr) -> io::Result<()> {
+    unsafe { ret(c::shm_unlink(c_str(name))) }
+}
+
+

src/backend/linux_raw/c.rs

@@ -24,6 +24,7 @@ pub(crate) use linux_raw_sys::general::epoll_event;
 
 #[cfg(any(
     feature = "fs",
+    feature = "shm",
     all(
         not(feature = "use-libc-auxv"),
         not(feature = "use-explicitly-provided-auxv"),

src/backend/linux_raw/conv.rs

@@ -298,6 +298,7 @@ pub(super) fn socklen_t<'a, Num: ArgNumber>(i: socklen_t) -> ArgReg<'a, Num> {
 
 #[cfg(any(
     feature = "fs",
+    feature = "shm",
     all(
         not(feature = "use-libc-auxv"),
         not(feature = "use-explicitly-provided-auxv"),

src/backend/linux_raw/mod.rs

@@ -27,6 +27,7 @@ mod vdso_wrappers;
 pub(crate) mod event;
 #[cfg(any(
     feature = "fs",
+    feature = "shm",
     all(
         not(feature = "use-libc-auxv"),
         not(feature = "use-explicitly-provided-auxv"),
@@ -67,6 +68,8 @@ pub(crate) mod pty;
 pub(crate) mod rand;
 #[cfg(feature = "runtime")]
 pub(crate) mod runtime;
+#[cfg(feature = "shm")]
+pub(crate) mod shm;
 #[cfg(feature = "system")]
 pub(crate) mod system;
 #[cfg(feature = "termios")]
@@ -94,6 +97,7 @@ pub(crate) mod prctl;
 #[cfg(any(
     feature = "fs",
     feature = "process",
+    feature = "shm",
     feature = "thread",
     all(
         not(feature = "use-libc-auxv"),

src/backend/linux_raw/shm/mod.rs

@@ -0,0 +1 @@
+pub(crate) mod syscalls;

src/backend/linux_raw/shm/syscalls.rs

@@ -0,0 +1,48 @@
+use std::ffi::CStr;
+
+use crate::fd::OwnedFd;
+use crate::backend::fs::{
+    syscalls::{open, unlink},
+    types::{Mode, OFlags},
+};
+use crate::io;
+
+const NAME_MAX: usize = 255;
+const SHM_DIR: &[u8] = b"/dev/shm/";
+
+fn get_shm_name(name: &CStr) -> io::Result<([u8; NAME_MAX + SHM_DIR.len() + 1], usize)> {
+    let name = name.to_bytes();
+
+    if name.len() > NAME_MAX {
+        return Err(io::Errno::NAMETOOLONG);
+    }
+
+    let num_slashes = name.into_iter().take_while(|x| **x == b'/').count();
+    let after_slashes = &name[num_slashes..];
+    if after_slashes.is_empty()
+        || after_slashes == b"."
+        || after_slashes == b".."
+        || after_slashes.contains(&b'/')
+    {
+        return Err(io::Errno::INVAL);
+    }
+
+    let mut path = [0; NAME_MAX + SHM_DIR.len() + 1];
+    path[..SHM_DIR.len()].copy_from_slice(SHM_DIR);
+    path[SHM_DIR.len()..SHM_DIR.len() + name.len()].copy_from_slice(name);
+    Ok((path, SHM_DIR.len() + name.len() + 1))
+}
+
+pub(crate) fn shm_open(name: &CStr, oflags: OFlags, mode: Mode) -> io::Result<OwnedFd> {
+    let (path, len) = get_shm_name(name)?;
+    open(
+        CStr::from_bytes_with_nul(&path[..len]).unwrap(),
+        oflags,
+        mode,
+    )
+}
+
+pub(crate) fn shm_unlink(name: &CStr) -> io::Result<()> {
+    let (path, len) = get_shm_name(name)?;
+    unlink(CStr::from_bytes_with_nul(&path[..len]).unwrap())
+}

src/lib.rs

@@ -219,7 +219,7 @@ pub mod net;
 #[cfg_attr(doc_cfg, doc(cfg(feature = "param")))]
 pub mod param;
 #[cfg(not(windows))]
-#[cfg(any(feature = "fs", feature = "mount", feature = "net"))]
+#[cfg(any(feature = "fs", feature = "mount", feature = "net", feature = "shm"))]
 #[cfg_attr(
     doc_cfg,
     doc(cfg(any(feature = "fs", feature = "mount", feature = "net")))
@@ -246,6 +246,9 @@ pub mod pty;
 #[cfg(feature = "rand")]
 #[cfg_attr(doc_cfg, doc(cfg(feature = "rand")))]
 pub mod rand;
+#[cfg(not(any(target_os = "android", target_os = "espidf", target_os = "wasi")))]
+#[cfg(feature = "shm")]
+pub mod shm;
 #[cfg(not(windows))]
 #[cfg(feature = "stdio")]
 #[cfg_attr(doc_cfg, doc(cfg(feature = "stdio")))]
@@ -285,15 +288,18 @@ pub(crate) mod mount;
 // reading procfs.
 #[cfg(not(windows))]
 #[cfg(not(feature = "fs"))]
-#[cfg(all(
-    linux_raw,
-    not(feature = "use-libc-auxv"),
-    not(feature = "use-explicitly-provided-auxv"),
-    any(
-        feature = "param",
-        feature = "runtime",
-        feature = "time",
-        target_arch = "x86",
+#[cfg(any(
+    feature = "shm",
+    all(
+        linux_raw,
+        not(feature = "use-libc-auxv"),
+        not(feature = "use-explicitly-provided-auxv"),
+        any(
+            feature = "param",
+            feature = "runtime",
+            feature = "time",
+            target_arch = "x86",
+        )
     )
 ))]
 #[cfg_attr(doc_cfg, doc(cfg(feature = "fs")))]
@@ -339,6 +345,7 @@ mod signal;
 #[cfg(any(
     feature = "fs",
     feature = "runtime",
+    feature = "shm",
     feature = "thread",
     feature = "time",
     all(
@@ -358,6 +365,7 @@ mod timespec;
 #[cfg(any(
     feature = "fs",
     feature = "process",
+    feature = "shm",
     feature = "thread",
     all(
         linux_raw,

src/shm.rs

@@ -0,0 +1,34 @@
+//! POSIX shared memory
+
+use crate::backend::fs::types::{Mode, OFlags};
+use crate::fd::OwnedFd;
+use crate::{backend, io, path};
+
+/// `shm_open(name, oflags, mode)`—Opens a shared memory object.
+///
+/// For portability, `name` should begin with a slash, contain no other slashes,
+/// and be no longer than an implementation-defined limit (255 on Linux).
+///
+/// # References
+///  - [POSIX]
+///  - [Linux]
+///
+/// [POSIX]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/shm_open.html
+/// [Linux]: https://man7.org/linux/man-pages/man3/shm_open.3.html
+#[inline]
+pub fn shm_open<P: path::Arg>(name: P, flags: OFlags, mode: Mode) -> io::Result<OwnedFd> {
+    name.into_with_c_str(|name| backend::shm::syscalls::shm_open(name, flags, mode))
+}
+
+/// `shm_unlink(name)`—Unlinks a shared memory object.
+///
+/// # References
+///  - [POSIX]
+///  - [Linux]
+///
+/// [POSIX]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/shm_unlink.html
+/// [Linux]: https://man7.org/linux/man-pages/man3/shm_unlink.3.html
+#[inline]
+pub fn shm_unlink<P: path::Arg>(name: P) -> io::Result<()> {
+    name.into_with_c_str(|name| backend::shm::syscalls::shm_unlink(name))
+}