systemd: add fd-store support

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

proxmox-systemd/src/notify.rs

@@ -1,5 +1,6 @@
-use std::ffi::CString;
+use std::ffi::{c_char, c_void, CStr, CString};
 use std::io;
+use std::os::fd::{AsFd, AsRawFd, RawFd};
 
 use crate::sys;
 
@@ -41,3 +42,86 @@ impl SystemdNotify {
 pub fn barrier(timeout: u64) -> Result<(), io::Error> {
     sys::check_call(unsafe { sys::sd_notify_barrier(0, timeout) }).map(drop)
 }
+
+/// Store a set of file descriptors in systemd's file descriptor store for this service.
+pub fn store_fds(name: &str, fds: &[RawFd]) -> Result<(), io::Error> {
+    validate_name(name)?;
+
+    let message = CString::new(format!("FDSTORE=1\nFDNAME={name}"))?;
+
+    sys::check_call(unsafe {
+        sys::sd_pid_notify_with_fds(0, 0, message.as_ptr(), fds.as_ptr(), fds.len() as _)
+    })
+    .map(drop)
+}
+
+/// Store a file descriptor in systemd's file descriptor store for this service.
+pub fn store_fd<F: AsFd + ?Sized>(name: &str, fds: &F) -> Result<(), io::Error> {
+    store_fds(name, &[fds.as_fd().as_raw_fd()])
+}
+
+/// Validate a name for the `FDNAME=` argument (see `man sd_pid_notify_with_fds`).
+fn validate_name(name: &str) -> Result<(), io::Error> {
+    for b in name.as_bytes() {
+        if *b == b':' || b.is_ascii_control() {
+            return Err(io::Error::new(
+                io::ErrorKind::Other,
+                "invalid file descriptor name",
+            ));
+        }
+    }
+    Ok(())
+}
+
+/// An iterator over the file descriptor names in the systemd file descriptor store.
+pub struct ListenFdNames {
+    ptr: *mut *mut c_char,
+    cur: usize,
+    len: usize,
+}
+
+impl ListenFdNames {
+    /// Query the file descriptor names and numbers stored in the systemd file descriptor store.
+    pub fn query() -> Result<Self, io::Error> {
+        let mut names = std::ptr::null_mut();
+        let count = sys::check_call(unsafe { sys::sd_listen_fds_with_names(0, &mut names) })?;
+        Ok(Self {
+            ptr: names,
+            cur: 0,
+            len: count as usize,
+        })
+    }
+
+    fn as_array(&self) -> &[*mut c_char] {
+        if self.ptr.is_null() {
+            &[]
+        } else {
+            unsafe { std::slice::from_raw_parts(self.ptr, self.len) }
+        }
+    }
+}
+
+impl Drop for ListenFdNames {
+    fn drop(&mut self) {
+        for name in self.as_array() {
+            unsafe { libc::free(*name as *mut c_void) }
+        }
+    }
+}
+
+impl Iterator for ListenFdNames {
+    type Item = (RawFd, Result<String, std::string::FromUtf8Error>);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let names = self.as_array();
+        if self.cur >= names.len() {
+            return None;
+        }
+
+        let ptr = names[self.cur] as *const c_char;
+        let fd_num = (self.cur as RawFd) + sys::LISTEN_FDS_START;
+        self.cur += 1;
+        let name = String::from_utf8(unsafe { CStr::from_ptr(ptr) }.to_bytes().to_vec());
+        Some((fd_num, name))
+    }
+}

proxmox-systemd/src/sys.rs

@@ -1,5 +1,8 @@
-use std::ffi::{c_char, c_int, c_uchar};
+use std::ffi::{c_char, c_int, c_uchar, c_uint};
 use std::io;
+use std::os::fd::RawFd;
+
+pub const LISTEN_FDS_START: RawFd = 3;
 
 #[link(name = "systemd")]
 extern "C" {
@@ -10,6 +13,17 @@ extern "C" {
     ) -> c_int;
     pub fn sd_notify(unset_environment: c_int, state: *const c_char) -> c_int;
     pub fn sd_notify_barrier(unset_environment: c_int, timeout: u64) -> c_int;
+    pub fn sd_pid_notify_with_fds(
+        pid: libc::pid_t,
+        unset_environment: c_int,
+        state: *const c_char,
+        fds: *const c_int,
+        n_fds: c_uint,
+    ) -> c_int;
+    pub fn sd_listen_fds_with_names(
+        unset_environment: c_int,
+        names: *mut *mut *mut c_char,
+    ) -> c_int;
 }
 
 pub fn check_call(ret: c_int) -> Result<c_int, io::Error> {