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Fix ordering of erofs images in overlay fs #162

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Merged
slp merged 1 commit into from
Mar 28, 2025
+56 −36
Merged

Fix ordering of erofs images in overlay fs #162

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92 changes: 56 additions & 36 deletions crates/muvm/src/guest/mount.rs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
use std::collections::HashSet;
use std::ffi::CString;
use std::fs::{read_dir, read_link, File};
use std::fs::{read_dir, read_link, DirEntry, File};
use std::io::Write;
use std::os::fd::AsFd;
use std::path::{Path, PathBuf};
Expand All @@ -14,7 +14,10 @@ use rustix::mount::{
use rustix::path::Arg;
use serde_json::json;

fn make_tmpfs(dir: &str) -> Result<()> {
fn make_tmpfs<P>(dir: P) -> Result<()>
where
P: rustix::path::Arg,
{
mount2(
Some("tmpfs"),
dir,
Expand All @@ -25,7 +28,10 @@ fn make_tmpfs(dir: &str) -> Result<()> {
.context("Failed to mount tmpfs")
}

fn mkdir_fex(dir: &str) {
fn mkdir_fex<P>(dir: P)
where
P: rustix::path::Arg,
{
// Must succeed since /run/ was just mounted and is now an empty tmpfs.
mkdir(
dir,
Expand All @@ -39,19 +45,19 @@ fn do_mount_recursive_bind(source: &str, target: PathBuf) -> Result<()> {
// the /run/muvm-host thing.
if source == "/run" {
mount_bind(source, &target)
.context(format!("Failed to mount {:?} on {:?}", &source, &target))?;
.with_context(|| format!("Failed to mount {source:?} on {target:?}"))?;
let host = target.join("muvm-host");
mount_bind("/", &host).context(format!("Failed to mount / on {:?}", &host))?;
mount_bind("/", &host).with_context(|| format!("Failed to mount / on {host:?}"))?;
} else {
mount_recursive_bind(source, &target)
.context(format!("Failed to mount {:?} on {:?}", &source, &target))?;
.with_context(|| format!("Failed to mount {source:?} on {target:?}"))?;
}
Ok(())
}

fn mount_fex_rootfs(merged_rootfs: bool) -> Result<()> {
let dir = "/run/fex-emu/";
let dir_rootfs = dir.to_string() + "rootfs";
let dir = Path::new("/run/fex-emu/");
let dir_rootfs = dir.join("rootfs");

// Make base directories
mkdir_fex(dir);
Expand All @@ -69,22 +75,31 @@ fn mount_fex_rootfs(merged_rootfs: bool) -> Result<()> {
}

// Find /dev/vd*
for x in read_dir("/dev").unwrap() {
let file = x.unwrap();
let name = file.file_name().into_string().unwrap();
if !name.starts_with("vd") {
continue;
}

let path = file.path().into_os_string().into_string().unwrap();
let dir = dir.to_string() + &name;

let mut dev_vd_entries: Vec<DirEntry> = read_dir("/dev")
.context("Failed to read directory `/dev`")?
.collect::<Result<Vec<_>, _>>()
.context("Failed to read directory entry in `/dev`")?
.into_iter()
.filter(|entry| {
entry
.file_name()
.into_string()
.expect("file_name should not contain invalid UTF-8")
.starts_with("vd")
})
.collect();
// [readdir(3)](https://man7.org/linux/man-pages/man3/readdir.3.html#NOTES)
//
// > The order in which filenames are read by successive calls to readdir() depends on the
// > filesystem implementation; it is unlikely that the names will be sorted in any fashion.
dev_vd_entries.sort_unstable_by_key(|entry| entry.file_name());
for entry in dev_vd_entries {
let target_dir = dir.join(entry.file_name());
// Mount the erofs images.
mkdir_fex(&dir);
mount2(Some(path), dir.clone(), Some("erofs"), flags, None)
.context("Failed to mount erofs")
.unwrap();
images.push(dir);
mkdir_fex(&target_dir);
mount2(Some(entry.path()), &target_dir, Some("erofs"), flags, None)
.context("Failed to mount erofs")?;
images.push(target_dir);
}

if images.is_empty() {
Expand All @@ -99,7 +114,7 @@ fn mount_fex_rootfs(merged_rootfs: bool) -> Result<()> {
// For merged rootfs mode, we need to overlay subtrees separately
// onto the real rootfs. First, insert the real rootfs as the
// bottom-most "image".
images.insert(0, "/".to_owned());
images.insert(0, PathBuf::from("/"));

let mut merge_dirs = HashSet::new();
let mut non_dirs = HashSet::new();
Expand All @@ -115,25 +130,25 @@ fn mount_fex_rootfs(merged_rootfs: bool) -> Result<()> {
continue;
};
let source = entry.path();
let file_name = entry.file_name().to_str().unwrap().to_owned();
let target = Path::new(&dir_rootfs).join(&file_name);
let file_name = entry.file_name();
let target = dir_rootfs.join(&file_name);

if file_type.is_file() {
// File in the root fs, bind mount it from the uppermost layer
if non_dirs.insert(file_name) {
File::create(&target)?;
mount_bind(&source, &target)?;
mount_bind(source, target)?;
}
} else if file_type.is_symlink() {
// Symlink in the root fs, create it from the uppermost layer
if non_dirs.insert(file_name) {
let symlink_target = read_link(source)?;
symlink(&symlink_target, &target)?;
symlink(symlink_target, target)?;
}
} else {
// Directory, so we potentially have to overlayfs it
if merge_dirs.insert(file_name) {
mkdir_fex(target.as_str()?);
mkdir_fex(target);
}
}
}
Expand All @@ -142,11 +157,11 @@ fn mount_fex_rootfs(merged_rootfs: bool) -> Result<()> {
// Now, go through each potential merged dir and figure out which
// layers have it, then mount an overlayfs (or bind if one layer).
for dir in merge_dirs {
let target = Path::new(&dir_rootfs).join(&dir);
let target = dir_rootfs.join(&dir);
let mut layers = Vec::new();

for image in images.iter() {
let source = Path::new(image).join(&dir);
let source = image.join(&dir);
if source.is_dir() {
layers.push(source.as_str().unwrap().to_owned());
}
Expand All @@ -161,8 +176,8 @@ fn mount_fex_rootfs(merged_rootfs: bool) -> Result<()> {
layers[0] = "/run/muvm-host/etc".to_owned();
}
let opts = format!(
"lowerdir={},metacopy=off,redirect_dir=nofollow,userxattr",
layers.into_iter().rev().collect::<Vec<String>>().join(":")
"lowerdir={lowerdir},metacopy=off,redirect_dir=nofollow,userxattr",
lowerdir = layers.into_iter().rev().collect::<Vec<String>>().join(":")
);
let opts = CString::new(opts).unwrap();
let overlay = "overlay".to_string();
Expand All @@ -176,14 +191,19 @@ fn mount_fex_rootfs(merged_rootfs: bool) -> Result<()> {
// Special case: Put back the /etc/resolv.conf overlay on top
overlay_file(
"/etc/resolv.conf",
&(dir_rootfs.clone() + "/etc/resolv.conf"),
dir_rootfs.join("etc/resolv.conf").as_str().unwrap(),
)?;
} else {
if images.len() >= 2 {
// Overlay the mounts together.
let opts = format!(
"lowerdir={}",
images.into_iter().rev().collect::<Vec<String>>().join(":")
"lowerdir={lowerdir}",
lowerdir = images
.into_iter()
.rev()
.map(|path| path.as_str().unwrap().to_owned())
.collect::<Vec<_>>()
.join(":")
);
let opts = CString::new(opts).unwrap();
let overlay = "overlay".to_string();
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