feat: support read-only filesystem mounts#85
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Pull request overview
This PR adds support for marking preopened host filesystem mounts as read-only, and enforces that policy in the host-side fs_* tool handlers so guest write-like operations are denied while reads continue to work.
Changes:
- Extend
Preopenwith aread_only: boolflag and a builder-style.read_only()helper. - Track the read-only flag per mount in
FsRouterand gate write operations viarequire_writable(). - Add unit tests covering read-only behavior across the affected fs_* operations; bump host crate version to
0.7.0.
Reviewed changes
Copilot reviewed 2 out of 3 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| host/src/lib.rs | Adds Preopen::read_only, propagates mount RO state into FsRouter, gates write operations, and adds RO mount tests. |
| host/Cargo.toml | Bumps crate version to 0.7.0. |
| host/Cargo.lock | Updates lockfile to reflect version bump. |
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| /// Return a copy of this preopen with `read_only` set to `true`. | ||
| pub fn read_only(mut self) -> Self { | ||
| self.read_only = true; | ||
| self | ||
| } |
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| fn require_writable<'a>(&'a self, path: &'a str) -> Result<(&'a FsSandbox, &'a str)> { | ||
| let (fs, rel, ro) = self.route(path)?; | ||
| if ro { | ||
| return Err(anyhow!("read-only mount: write to {:?} denied", path)); | ||
| } | ||
| Ok((fs, rel)) |
Signed-off-by: danbugs <danilochiarlone@gmail.com>
Signed-off-by: danbugs <danilochiarlone@gmail.com>
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Linux Benchmarks
Details
| Benchmark suite | Current: 399c361 | Previous: 05c4d64 | Ratio |
|---|---|---|---|
hello_world (median) |
20 ms |
20 ms |
1 |
pandas (median) |
110 ms |
110 ms |
1 |
density (per VM) |
11 MB |
11 MB |
1 |
snapshot (disk) |
656 MiB |
656 MiB |
1 |
This comment was automatically generated by workflow using github-action-benchmark.
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Windows Benchmarks
Details
| Benchmark suite | Current: 399c361 | Previous: 05c4d64 | Ratio |
|---|---|---|---|
hello_world (median) |
379 ms |
320 ms |
1.18 |
pandas (median) |
1090 ms |
855 ms |
1.27 |
density (per VM) |
11 MB |
11 MB |
1 |
snapshot (disk) |
663 MiB |
663 MiB |
1 |
This comment was automatically generated by workflow using github-action-benchmark.
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Summary
read_only: boolfield toPreopenwith a builder-style.read_only()methodFsRoutercarries the flag per-mount and exposesrequire_writable()which gates all write operationsfs_write,fs_write_bytes,fs_truncate,fs_mkdir, andfs_unlinkreturn"read-only mount: write to <path> denied"when targeting a read-only preopenfs_read,fs_read_bytes,fs_list,fs_stat) work normally on read-only mountsTest plan
readonly_mount_allows_reads— reads succeed on RO mountreadonly_mount_blocks_fs_write— text write deniedreadonly_mount_blocks_fs_write_bytes— binary write deniedreadonly_mount_blocks_fs_truncate— truncate deniedreadonly_mount_blocks_fs_mkdir— mkdir deniedreadonly_mount_blocks_fs_unlink— unlink denied, file preservedmixed_rw_and_ro_mounts— RW and RO mounts coexist correctly