add tools/cpio encoding module

Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>

src/tools.rs

@@ -23,6 +23,7 @@ pub mod async_io;
 pub mod borrow;
 pub mod cert;
 pub mod compression;
+pub mod cpio;
 pub mod daemon;
 pub mod disks;
 pub mod format;

src/tools/cpio.rs

@@ -0,0 +1,73 @@
+//! Provides a very basic "newc" format cpio encoder.
+//! See 'man 5 cpio' for format details, as well as:
+//! https://www.kernel.org/doc/html/latest/driver-api/early-userspace/buffer-format.html
+//! This does not provide full support for the format, only what is needed to include files in an
+//! initramfs intended for a linux kernel.
+use anyhow::{bail, Error};
+use std::ffi::{CString, CStr};
+use tokio::io::{copy, AsyncRead, AsyncReadExt, AsyncWrite, AsyncWriteExt};
+
+/// Write a cpio file entry to an AsyncWrite.
+pub async fn append_file<W: AsyncWrite + Unpin, R: AsyncRead + Unpin>(
+    mut target: W,
+    content: R,
+    name: &CStr,
+    inode: u16,
+    mode: u16,
+    uid: u16,
+    gid: u16,
+    // negative mtimes are generally valid, but cpio defines all fields as unsigned
+    mtime: u64,
+    // c_filesize has 8 bytes, but man page claims that 4 GB files are the maximum, let's be safe
+    size: u32,
+) -> Result<(), Error> {
+    let name = name.to_bytes_with_nul();
+
+    target.write_all(b"070701").await?; // c_magic
+    print_cpio_hex(&mut target, inode as u64).await?; // c_ino
+    print_cpio_hex(&mut target, mode as u64).await?; // c_mode
+    print_cpio_hex(&mut target, uid as u64).await?; // c_uid
+    print_cpio_hex(&mut target, gid as u64).await?; // c_gid
+    print_cpio_hex(&mut target, 0).await?; // c_nlink
+    print_cpio_hex(&mut target, mtime as u64).await?; // c_mtime
+    print_cpio_hex(&mut target, size as u64).await?; // c_filesize
+    print_cpio_hex(&mut target, 0).await?; // c_devmajor
+    print_cpio_hex(&mut target, 0).await?; // c_devminor
+    print_cpio_hex(&mut target, 0).await?; // c_rdevmajor
+    print_cpio_hex(&mut target, 0).await?; // c_rdevminor
+    print_cpio_hex(&mut target, name.len() as u64).await?; // c_namesize
+    print_cpio_hex(&mut target, 0).await?; // c_check (ignored for newc)
+
+    target.write_all(name).await?;
+    let header_size = 6 + 8*13 + name.len();
+    let mut name_pad = header_size;
+    while name_pad & 3 != 0 {
+        target.write_u8(0).await?;
+        name_pad += 1;
+    }
+
+    let mut content = content.take(size as u64);
+    let copied = copy(&mut content, &mut target).await?;
+    if copied < size as u64 {
+        bail!("cpio: not enough data, or size to big - encoding invalid");
+    }
+    let mut data_pad = copied;
+    while data_pad & 3 != 0 {
+        target.write_u8(0).await?;
+        data_pad += 1;
+    }
+
+    Ok(())
+}
+
+/// Write the TRAILER!!! file to an AsyncWrite, signifying the end of a cpio archive. Note that you
+/// can immediately add more files after, to create a concatenated archive, the kernel for example
+/// will merge these upon loading an initramfs.
+pub async fn append_trailer<W: AsyncWrite + Unpin>(target: W) -> Result<(), Error> {
+    let name = CString::new("TRAILER!!!").unwrap();
+    append_file(target, tokio::io::empty(), &name, 0, 0, 0, 0, 0, 0).await
+}
+
+async fn print_cpio_hex<W: AsyncWrite + Unpin>(target: &mut W, value: u64) -> Result<(), Error> {
+    target.write_all(format!("{:08x}", value).as_bytes()).await.map_err(|e| e.into())
+}