Implement creation of SysV IPC message queues

This adds the `sysvmq` package which handles SysV IPC message queues.
For consistency the parameter for `permissions` is renamed to `mode`
also for POSIX message queues.

.gitignore

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+/target
+Cargo.lock

Cargo.toml

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+[package]
+name = "sysvmq"
+version = "0.1.0"
+edition = "2018"
+authors = ["finga <mqrs@onders.org>"]
+repository = "https://git.onders.org/finga/mqrs"
+license = "GPL-3.0-or-later"
+
+[dependencies]
+libc = "0.2.98"
+thiserror = "1.0.26"
+nix = "0.21.0"

src/lib.rs

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+use libc::{
+    msgget, IPC_CREAT, IPC_EXCL, IPC_INFO, IPC_NOWAIT, IPC_PRIVATE, IPC_RMID, IPC_SET, IPC_STAT,
+    MSG_COPY, MSG_EXCEPT, MSG_INFO, MSG_NOERROR, MSG_STAT,
+};
+use nix::errno::{errno, Errno};
+use std::{marker::PhantomData, num::ParseIntError};
+use thiserror::Error;
+
+#[derive(Debug, Error)]
+pub enum SysvMqError {
+    #[error("SysV message queue: {0}")]
+    ErrnoError(&'static str),
+    #[error("No message queue found with key {0}")]
+    KeyNotFound(i32),
+    #[error("IO Error: {0}")]
+    IoError(#[from] std::io::Error),
+    #[error("Parse Error: {0}")]
+    ParserError(#[from] ParseIntError),
+}
+
+/// IPC bit flags
+#[repr(i32)]
+pub enum Flags {
+    /// Create key if key does not exist.
+    CreateKey = IPC_CREAT,
+    /// Fail if key exists.
+    Exclusive = IPC_EXCL,
+    /// Return error on wait.
+    NoWait = IPC_NOWAIT,
+    /// No error if message is too big.
+    NoError = MSG_NOERROR,
+    /// Receive any message except of specified type.
+    Except = MSG_EXCEPT,
+    /// Copy (not remove) all queue messages.
+    Copy = MSG_COPY,
+    /// Private key (Special key value).
+    Private = IPC_PRIVATE,
+}
+
+/// Commands for `msgctl()`
+#[repr(i32)]
+pub enum ControlCommands {
+    /// Remove identifier (Control command for `msgctl`, `semctl`, and `shmctl`).
+    Remove = IPC_RMID,
+    /// Set `ipc_perm` options (Control command for `msgctl`, `semctl`, and `shmctl`).
+    SetPerm = IPC_SET,
+    /// Get `ipc_perm` options (Control command for `msgctl`, `semctl`, and `shmctl`).
+    GetPerm = IPC_STAT,
+    /// See ipcs (Control command for `msgctl`, `semctl`, and `shmctl`).
+    IpcInfo = IPC_INFO,
+    /// IPCS control command.
+    Stat = MSG_STAT,
+    /// IPCS control command.
+    MsgInfo = MSG_INFO,
+}
+
+pub struct SysvMq<T> {
+    pub id: i32,
+    pub key: i32,
+    message_mask: i32,
+    mode: i32,
+    types: PhantomData<T>,
+}
+
+impl<T> SysvMq<T> {
+    pub fn create(&mut self, key: i32) -> Result<&Self, SysvMqError> {
+        self.key = key;
+        self.id = unsafe { msgget(self.key, Flags::CreateKey as i32 | self.mode) };
+
+        match self.id {
+            -1 => Err(SysvMqError::ErrnoError(Errno::from_i32(errno()).desc())),
+            _ => Ok(self),
+        }
+    }
+
+    pub fn open(mut self, key: i32) -> Result<Self, SysvMqError> {
+        self.key = key;
+        self.id = unsafe { msgget(self.key, self.mode) };
+
+        match self.id {
+            -1 => Err(SysvMqError::ErrnoError(Errno::from_i32(errno()).desc())),
+            _ => Ok(self),
+        }
+    }
+
+    pub fn mode(&mut self, mode: i32) -> &Self {
+        self.mode = mode;
+        self
+    }
+
+    pub fn nonblocking(&mut self) -> &Self {
+        self.message_mask |= Flags::NoWait as i32;
+        self
+    }
+
+    pub fn new() -> Self {
+        SysvMq {
+            id: -1,
+            key: 0,
+            message_mask: 0,
+            mode: 0o644,
+            types: PhantomData,
+        }
+    }
+}
+
+impl<T> Default for SysvMq<T> {
+    fn default() -> Self {
+        Self::new()
+    }
+}