Add index_to_name_inlined

src/backend/libc/net/netdevice.rs

@@ -2,15 +2,11 @@
 
 #![allow(unsafe_code)]
 
-#[cfg(feature = "alloc")]
-use crate::alloc::string::String;
 use crate::backend::c;
 use crate::backend::io::syscalls::ioctl;
 use crate::fd::BorrowedFd;
 use crate::io;
-#[cfg(feature = "alloc")]
-use c::SIOCGIFNAME;
-use c::{__c_anonymous_ifr_ifru, c_char, ifreq, IFNAMSIZ, SIOCGIFINDEX};
+use c::{__c_anonymous_ifr_ifru, c_char, ifreq, IFNAMSIZ, SIOCGIFINDEX, SIOCGIFNAME};
 
 pub(crate) fn name_to_index(fd: BorrowedFd<'_>, if_name: &str) -> io::Result<u32> {
     let if_name_bytes = if_name.as_bytes();
@@ -31,8 +27,7 @@ pub(crate) fn name_to_index(fd: BorrowedFd<'_>, if_name: &str) -> io::Result<u32
     Ok(index as u32)
 }
 
-#[cfg(feature = "alloc")]
-pub(crate) fn index_to_name(fd: BorrowedFd<'_>, index: u32) -> io::Result<String> {
+pub(crate) fn index_to_name(fd: BorrowedFd<'_>, index: u32) -> io::Result<(usize, [u8; 16])> {
     let mut ifreq = ifreq {
         ifr_name: [0; 16],
         ifr_ifru: __c_anonymous_ifr_ifru {
@@ -43,12 +38,12 @@ pub(crate) fn index_to_name(fd: BorrowedFd<'_>, index: u32) -> io::Result<String
     unsafe { ioctl(fd, SIOCGIFNAME as _, &mut ifreq as *mut ifreq as _) }?;
 
     if let Some(nul_byte) = ifreq.ifr_name.iter().position(|char| *char == 0) {
-        let name: String = ifreq.ifr_name[..nul_byte]
-            .iter()
-            .map(|v| *v as u8 as char)
-            .collect();
+        let mut buf = [0u8; 16];
+        ifreq.ifr_name.iter().enumerate().for_each(|(idx, c)| {
+            buf[idx] = *c as u8;
+        });
 
-        Ok(name)
+        Ok((nul_byte, buf))
     } else {
         Err(io::Errno::INVAL)
     }

src/backend/linux_raw/net/netdevice.rs

@@ -8,12 +8,8 @@ use crate::io;
 use core::ptr::addr_of_mut;
 use core::{slice, str};
 use linux_raw_sys::ctypes::c_char;
-use linux_raw_sys::ioctl::SIOCGIFINDEX;
-#[cfg(feature = "alloc")]
-use linux_raw_sys::ioctl::SIOCGIFNAME;
+use linux_raw_sys::ioctl::{SIOCGIFINDEX, SIOCGIFNAME};
 use linux_raw_sys::net::{ifreq, ifreq__bindgen_ty_1, ifreq__bindgen_ty_2, IFNAMSIZ};
-#[cfg(feature = "alloc")]
-use {alloc::borrow::ToOwned, alloc::string::String};
 
 pub(crate) fn name_to_index(fd: BorrowedFd<'_>, if_name: &str) -> io::Result<u32> {
     let if_name_bytes = if_name.as_bytes();
@@ -40,8 +36,7 @@ pub(crate) fn name_to_index(fd: BorrowedFd<'_>, if_name: &str) -> io::Result<u32
     Ok(index as u32)
 }
 
-#[cfg(feature = "alloc")]
-pub(crate) fn index_to_name(fd: BorrowedFd<'_>, index: u32) -> io::Result<String> {
+pub(crate) fn index_to_name(fd: BorrowedFd<'_>, index: u32) -> io::Result<(usize, [u8; 16])> {
     let mut ifreq = ifreq {
         ifr_ifrn: ifreq__bindgen_ty_1 { ifrn_name: [0; 16] },
         ifr_ifru: ifreq__bindgen_ty_2 {
@@ -61,9 +56,10 @@ pub(crate) fn index_to_name(fd: BorrowedFd<'_>, index: u32) -> io::Result<String
         let ifrn_name =
             unsafe { slice::from_raw_parts(ifrn_name.as_ptr().cast::<u8>(), ifrn_name.len()) };
 
-        str::from_utf8(ifrn_name)
-            .map_err(|_| io::Errno::ILSEQ)
-            .map(ToOwned::to_owned)
+        let mut name_buf = [0; 16];
+        name_buf[..ifrn_name.len()].copy_from_slice(ifrn_name);
+
+        Ok((nul_byte, name_buf))
     } else {
         Err(io::Errno::INVAL)
     }

src/net/netdevice.rs

@@ -19,7 +19,7 @@
 use crate::fd::AsFd;
 use crate::io;
 #[cfg(feature = "alloc")]
-use alloc::string::String;
+use alloc::{borrow::ToOwned, string::String};
 
 /// `ioctl(fd, SIOCGIFINDEX, ifreq)`—Returns the interface index for a given
 /// name.
@@ -42,6 +42,8 @@ pub fn name_to_index<Fd: AsFd>(fd: Fd, if_name: &str) -> io::Result<u32> {
 ///
 /// See the [module-level documentation] for information about `fd` usage.
 ///
+/// See also [`index_to_name_inlined`] which does not require `alloc` feature.
+///
 /// # References
 ///  - [Linux]
 ///
@@ -52,12 +54,84 @@ pub fn name_to_index<Fd: AsFd>(fd: Fd, if_name: &str) -> io::Result<u32> {
 #[cfg(feature = "alloc")]
 #[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
 pub fn index_to_name<Fd: AsFd>(fd: Fd, index: u32) -> io::Result<String> {
-    crate::backend::net::netdevice::index_to_name(fd.as_fd(), index)
+    let (len, ifrn_name) = crate::backend::net::netdevice::index_to_name(fd.as_fd(), index)?;
+
+    core::str::from_utf8(&ifrn_name[..len])
+        .map_err(|_| io::Errno::ILSEQ)
+        .map(ToOwned::to_owned)
+}
+
+/// `ioctl(fd, SIOCGIFNAME, ifreq)`—Returns the interface name for a given
+/// index.
+///
+/// See the [module-level documentation] for information about `fd` usage.
+///
+/// # References
+///  - [Linux]
+///
+/// [module-level documentation]: self
+/// [Linux]: https://man7.org/linux/man-pages/man7/netdevice.7.html
+#[inline]
+#[doc(alias = "SIOCGIFNAME")]
+pub fn index_to_name_inlined<Fd: AsFd>(fd: Fd, index: u32) -> io::Result<InlinedName> {
+    let (len, ifrn_name) = crate::backend::net::netdevice::index_to_name(fd.as_fd(), index)?;
+
+    // Check if the name is valid UTF-8.
+    core::str::from_utf8(&ifrn_name[..len])
+        .map_err(|_| io::Errno::ILSEQ)
+        .map(|_| InlinedName {
+            len,
+            name: ifrn_name,
+        })
+}
+
+/// The inlined interface name.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
+pub struct InlinedName {
+    len: usize,
+    name: [u8; 16],
+}
+
+impl InlinedName {
+    /// Returns the str representation of the inlined name.
+    pub fn as_str(&self) -> &str {
+        self.as_ref()
+    }
+
+    /// Returns the bytes representation of the inlined name.
+    pub fn as_bytes(&self) -> &[u8] {
+        self.as_ref()
+    }
+}
+
+impl AsRef<[u8]> for InlinedName {
+    fn as_ref(&self) -> &[u8] {
+        &self.name[..self.len]
+    }
+}
+
+impl AsRef<str> for InlinedName {
+    fn as_ref(&self) -> &str {
+        // SAFETY: `InlinedName` is constructed with valid UTF-8.
+        core::str::from_utf8(&self.name[..self.len]).unwrap()
+    }
+}
+
+impl core::borrow::Borrow<str> for InlinedName {
+    fn borrow(&self) -> &str {
+        self.as_ref()
+    }
+}
+
+impl core::fmt::Display for InlinedName {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        self.as_str().fmt(f)
+    }
 }
 
 #[cfg(test)]
 mod tests {
-    use crate::backend::net::netdevice::{index_to_name, name_to_index};
+    use super::{index_to_name, index_to_name_inlined, name_to_index};
     use crate::fd::AsFd;
     use crate::net::{AddressFamily, SocketFlags, SocketType};
 
@@ -81,6 +155,31 @@ mod tests {
         assert_eq!(Ok(loopback_index), name_to_index(fd.as_fd(), "lo"));
     }
 
+    #[test]
+    fn test_index_to_name_inlined() {
+        let fd = crate::net::socket_with(
+            AddressFamily::INET,
+            SocketType::DGRAM,
+            SocketFlags::CLOEXEC,
+            None,
+        )
+        .unwrap();
+
+        let loopback_index = std::fs::read_to_string("/sys/class/net/lo/ifindex")
+            .unwrap()
+            .as_str()
+            .split_at(1)
+            .0
+            .parse::<u32>()
+            .unwrap();
+        assert_eq!(
+            "lo",
+            index_to_name_inlined(fd.as_fd(), loopback_index)
+                .unwrap()
+                .as_str(),
+        );
+    }
+
     #[test]
     #[cfg(feature = "alloc")]
     fn test_index_to_name() {