treewide: refactor mkdir, write_file and read_file

mkdir, read_file write_file augment the error case with the path in the
error case. This is useful as we otherwise don't know which location
failed. This commit refactors the functions to take any argument that
coerces into a Path - which is implemented by many types.

mkdir now uses create_dir_all as it is not meant to fail if the
directory already exists.

Signed-off-by: Stefan Kerkmann <s.kerkmann@pengutronix.de>

src/main.rs

@@ -5,7 +5,7 @@ use std::env;
 use std::env::current_exe;
 use std::ffi::CString;
 use std::fmt::Write as _;
-use std::fs::{create_dir, read_to_string, File, OpenOptions};
+use std::fs::{File, OpenOptions};
 use std::io;
 use std::io::Write as _;
 use std::os::fd::{AsFd, AsRawFd, RawFd};
@@ -25,6 +25,7 @@ use nix::unistd::{chdir, chroot, dup2, execv, unlink};
 use systemd::{mount_systemd, shutdown};
 #[cfg(feature = "usb9pfs")]
 use usbg_9pfs::prepare_9pfs_gadget;
+use util::read_file;
 
 mod cmdline;
 #[cfg(feature = "dmverity")]
@@ -34,22 +35,10 @@ mod mount;
 mod systemd;
 #[cfg(feature = "usb9pfs")]
 mod usbg_9pfs;
+mod util;
 
 type Result<T> = std::result::Result<T, Box<dyn std::error::Error>>;
 
-pub fn mkdir(dir: &str) -> Result<()> {
-    if let Err(e) = create_dir(dir) {
-        if e.kind() != io::ErrorKind::AlreadyExists {
-            return Err(format!("Failed to create {dir}: {e}",).into());
-        }
-    }
-    Ok(())
-}
-
-fn read_file(filename: &str) -> std::result::Result<String, String> {
-    read_to_string(filename).map_err(|e| format!("Failed to read {filename}: {e}"))
-}
-
 /*
  * Setup stdout/stderr. The kernel will create /dev/console in the
  * initramfs, so we can use that.

src/mount.rs

@@ -7,7 +7,8 @@ use log::debug;
 use nix::mount::{mount, MsFlags};
 
 use crate::cmdline::CmdlineOptions;
-use crate::{mkdir, Result};
+use crate::util::mkdir;
+use crate::Result;
 
 pub fn do_mount(
     src: Option<&str>,

src/systemd.rs

@@ -10,7 +10,8 @@ use nix::sys::reboot::{reboot, RebootMode};
 
 use crate::cmdline::CmdlineOptions;
 use crate::mount::do_mount;
-use crate::{mkdir, Result};
+use crate::util::mkdir;
+use crate::Result;
 
 pub fn mount_systemd(options: &mut CmdlineOptions) -> Result<()> {
     do_mount(

src/usbg_9pfs.rs

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0-only
 
-use std::fs::{read_dir, write};
+use std::fs::read_dir;
 use std::os::unix::ffi::OsStrExt;
 use std::os::unix::fs::symlink;
 use std::{thread, time};
@@ -9,11 +9,8 @@ use log::debug;
 
 use crate::cmdline::CmdlineOptions;
 use crate::mount::mount_apivfs;
-use crate::{mkdir, Result};
-
-fn write_file<C: AsRef<[u8]>>(path: &str, content: C) -> Result<()> {
-    write(path, content).map_err(|e| format!("Failed to write to {path}: {e}").into())
-}
+use crate::util::{mkdir, write_file};
+use crate::Result;
 
 fn setup_9pfs_gadget(device: &String) -> Result<()> {
     debug!("Initializing USB 9pfs gadget ...");

src/util.rs

@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+use std::{
+    fs::{create_dir_all, read_to_string, write},
+    path::Path,
+};
+
+use crate::Result;
+
+pub(crate) fn mkdir(dir: impl AsRef<Path>) -> Result<()> {
+    create_dir_all(dir.as_ref()).map_err(|e| {
+        format!(
+            "Failed to create directory {}: {e}",
+            dir.as_ref().to_string_lossy()
+        )
+        .into()
+    })
+}
+
+pub(crate) fn read_file(filename: impl AsRef<Path>) -> Result<String> {
+    read_to_string(filename.as_ref()).map_err(|e| {
+        format!(
+            "Failed to read {}: {e}",
+            filename.as_ref().to_string_lossy()
+        )
+        .into()
+    })
+}
+
+pub(crate) fn write_file<C: AsRef<[u8]>>(path: impl AsRef<Path>, content: C) -> Result<()> {
+    write(&path, content).map_err(|e| {
+        format!(
+            "Failed to write to {}: {e}",
+            path.as_ref().to_string_lossy()
+        )
+        .into()
+    })
+}