From 77164e51e59878a6c4db6e19cc2343887020f526 Mon Sep 17 00:00:00 2001
From: Colin Walters <walters@verbum.org>
Date: Mon, 2 Oct 2023 14:17:08 -0400
Subject: [PATCH] lib: Add mountutil module

I copy/pasted the mountpoint check into bootc, but it'd
be better to centralize.
---
 lib/src/commit.rs    | 38 +------------------------------
 lib/src/lib.rs       |  1 +
 lib/src/mountutil.rs | 54 ++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 56 insertions(+), 37 deletions(-)
 create mode 100644 lib/src/mountutil.rs

diff --git a/lib/src/commit.rs b/lib/src/commit.rs
index d504d6fd..8277e7a8 100644
--- a/lib/src/commit.rs
+++ b/lib/src/commit.rs
@@ -3,13 +3,13 @@
 //! <https://github.com/ostreedev/ostree-rs-ext/issues/159>
 
 use crate::container_utils::require_ostree_container;
+use crate::mountutil::is_mountpoint;
 use anyhow::Context;
 use anyhow::Result;
 use camino::Utf8Path;
 use cap_std::fs::Dir;
 use cap_std_ext::cap_std;
 use cap_std_ext::dirext::CapStdExtDirExt;
-use io_lifetimes::AsFd;
 use rustix::fs::MetadataExt;
 use std::borrow::Cow;
 use std::convert::TryInto;
@@ -102,28 +102,6 @@ fn remove_all_on_mount_recurse(root: &Dir, rootdev: u64, path: &Path) -> Result<
     Ok(skipped)
 }
 
-/// Try to (heuristically) determine if the provided path is a mount root.
-fn is_mountpoint(root: &Dir, path: &Path) -> Result<Option<bool>> {
-    // https://github.com/systemd/systemd/blob/8fbf0a214e2fe474655b17a4b663122943b55db0/src/basic/mountpoint-util.c#L176
-    use rustix::fs::{AtFlags, StatxFlags};
-
-    // SAFETY(unwrap): We can infallibly convert an i32 into a u64.
-    let mountroot_flag: u64 = libc::STATX_ATTR_MOUNT_ROOT.try_into().unwrap();
-    match rustix::fs::statx(
-        root.as_fd(),
-        path,
-        AtFlags::NO_AUTOMOUNT | AtFlags::SYMLINK_NOFOLLOW,
-        StatxFlags::empty(),
-    ) {
-        Ok(r) => {
-            let present = (r.stx_attributes_mask & mountroot_flag) > 0;
-            Ok(present.then(|| r.stx_attributes & mountroot_flag > 0))
-        }
-        Err(e) if e == rustix::io::Errno::NOSYS => Ok(None),
-        Err(e) => Err(e.into()),
-    }
-}
-
 fn clean_subdir(root: &Dir, rootdev: u64) -> Result<()> {
     for entry in root.entries()? {
         let entry = entry?;
@@ -207,20 +185,6 @@ mod tests {
     use super::*;
     use cap_std_ext::cap_tempfile;
 
-    #[test]
-    fn test_is_mountpoint() -> Result<()> {
-        let root = cap_std::fs::Dir::open_ambient_dir("/", cap_std::ambient_authority())?;
-        let supported = is_mountpoint(&root, Path::new("/")).unwrap();
-        match supported {
-            Some(r) => assert!(r),
-            // If the host doesn't support statx, ignore this for now
-            None => return Ok(()),
-        }
-        let tmpdir = cap_tempfile::TempDir::new(cap_std::ambient_authority())?;
-        assert!(!is_mountpoint(&tmpdir, Path::new(".")).unwrap().unwrap());
-        Ok(())
-    }
-
     #[test]
     fn commit() -> Result<()> {
         let td = &cap_tempfile::tempdir(cap_std::ambient_authority())?;
diff --git a/lib/src/lib.rs b/lib/src/lib.rs
index 71956400..7d6a47ca 100644
--- a/lib/src/lib.rs
+++ b/lib/src/lib.rs
@@ -38,6 +38,7 @@ pub mod diff;
 pub mod ima;
 pub mod keyfileext;
 pub(crate) mod logging;
+pub mod mountutil;
 pub mod refescape;
 #[doc(hidden)]
 pub mod repair;
diff --git a/lib/src/mountutil.rs b/lib/src/mountutil.rs
new file mode 100644
index 00000000..55815116
--- /dev/null
+++ b/lib/src/mountutil.rs
@@ -0,0 +1,54 @@
+//! Helpers for interacting with mounts.
+
+use std::os::fd::AsFd;
+use std::path::Path;
+
+use anyhow::Result;
+use cap_std::fs::Dir;
+use cap_std_ext::cap_std;
+
+fn is_mountpoint_impl_statx(root: &Dir, path: &Path) -> Result<Option<bool>> {
+    // https://github.com/systemd/systemd/blob/8fbf0a214e2fe474655b17a4b663122943b55db0/src/basic/mountpoint-util.c#L176
+    use rustix::fs::{AtFlags, StatxFlags};
+
+    // SAFETY(unwrap): We can infallibly convert an i32 into a u64.
+    let mountroot_flag: u64 = libc::STATX_ATTR_MOUNT_ROOT.try_into().unwrap();
+    match rustix::fs::statx(
+        root.as_fd(),
+        path,
+        AtFlags::NO_AUTOMOUNT | AtFlags::SYMLINK_NOFOLLOW,
+        StatxFlags::empty(),
+    ) {
+        Ok(r) => {
+            let present = (r.stx_attributes_mask & mountroot_flag) > 0;
+            Ok(present.then(|| r.stx_attributes & mountroot_flag > 0))
+        }
+        Err(e) if e == rustix::io::Errno::NOSYS => Ok(None),
+        Err(e) => Err(e.into()),
+    }
+}
+
+/// Try to (heuristically) determine if the provided path is a mount root.
+pub fn is_mountpoint(root: &Dir, path: impl AsRef<Path>) -> Result<Option<bool>> {
+    is_mountpoint_impl_statx(root, path.as_ref())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use cap_std_ext::cap_tempfile;
+
+    #[test]
+    fn test_is_mountpoint() -> Result<()> {
+        let root = cap_std::fs::Dir::open_ambient_dir("/", cap_std::ambient_authority())?;
+        let supported = is_mountpoint(&root, Path::new("/")).unwrap();
+        match supported {
+            Some(r) => assert!(r),
+            // If the host doesn't support statx, ignore this for now
+            None => return Ok(()),
+        }
+        let tmpdir = cap_tempfile::TempDir::new(cap_std::ambient_authority())?;
+        assert!(!is_mountpoint(&tmpdir, Path::new(".")).unwrap().unwrap());
+        Ok(())
+    }
+}