Move loopdevice module to dm_rust lib
This is a generic module, not specific to apkdmverity. Will be reused
for unit-testing other dm- devices. Also, setup the test infra for
dm_rust module...
Bug: 250880499
Test: atest libdm_rust.test
Test: atest apkdmverity.test
Change-Id: I32971938908ea8c0213583885403910baac8be10
diff --git a/libs/devicemapper/src/loopdevice.rs b/libs/devicemapper/src/loopdevice.rs
new file mode 100644
index 0000000..bdbc0f6
--- /dev/null
+++ b/libs/devicemapper/src/loopdevice.rs
@@ -0,0 +1,196 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// `loopdevice` module provides `attach` and `detach` functions that are for attaching and
+// detaching a regular file to and from a loop device. Note that
+// `loopdev`(https://crates.io/crates/loopdev) is a public alternative to this. In-house
+// implementation was chosen to make Android-specific changes (like the use of the new
+// LOOP_CONFIGURE instead of the legacy LOOP_SET_FD + LOOP_SET_STATUS64 combo which is considerably
+// slower than the former).
+
+mod sys;
+
+use crate::util::*;
+use anyhow::{Context, Result};
+use data_model::DataInit;
+use libc::O_DIRECT;
+use std::fs::{File, OpenOptions};
+use std::mem::size_of;
+use std::os::unix::fs::OpenOptionsExt;
+use std::os::unix::io::AsRawFd;
+use std::path::{Path, PathBuf};
+use std::thread;
+use std::time::{Duration, Instant};
+
+use crate::loopdevice::sys::*;
+
+// These are old-style ioctls, thus *_bad.
+nix::ioctl_none_bad!(_loop_ctl_get_free, LOOP_CTL_GET_FREE);
+nix::ioctl_write_ptr_bad!(_loop_configure, LOOP_CONFIGURE, loop_config);
+nix::ioctl_none_bad!(_loop_clr_fd, LOOP_CLR_FD);
+
+fn loop_ctl_get_free(ctrl_file: &File) -> Result<i32> {
+ // SAFETY: this ioctl changes the state in kernel, but not the state in this process.
+ // The returned device number is a global resource; not tied to this process. So, we don't
+ // need to keep track of it.
+ Ok(unsafe { _loop_ctl_get_free(ctrl_file.as_raw_fd()) }?)
+}
+
+fn loop_configure(device_file: &File, config: &loop_config) -> Result<i32> {
+ // SAFETY: this ioctl changes the state in kernel, but not the state in this process.
+ Ok(unsafe { _loop_configure(device_file.as_raw_fd(), config) }?)
+}
+
+pub fn loop_clr_fd(device_file: &File) -> Result<i32> {
+ // SAFETY: this ioctl disassociates the loop device with `device_file`, where the FD will
+ // remain opened afterward. The association itself is kept for open FDs.
+ Ok(unsafe { _loop_clr_fd(device_file.as_raw_fd()) }?)
+}
+
+/// Creates a loop device and attach the given file at `path` as the backing store.
+pub fn attach<P: AsRef<Path>>(
+ path: P,
+ offset: u64,
+ size_limit: u64,
+ direct_io: bool,
+) -> Result<PathBuf> {
+ // Attaching a file to a loop device can make a race condition; a loop device number obtained
+ // from LOOP_CTL_GET_FREE might have been used by another thread or process. In that case the
+ // subsequent LOOP_CONFIGURE ioctl returns with EBUSY. Try until it succeeds.
+ //
+ // Note that the timing parameters below are chosen rather arbitrarily. In practice (i.e.
+ // inside Microdroid) we can't experience the race condition because `apkverity` is the only
+ // user of /dev/loop-control at the moment. This loop is mostly for testing where multiple
+ // tests run concurrently.
+ const TIMEOUT: Duration = Duration::from_secs(1);
+ const INTERVAL: Duration = Duration::from_millis(10);
+
+ let begin = Instant::now();
+ loop {
+ match try_attach(&path, offset, size_limit, direct_io) {
+ Ok(loop_dev) => return Ok(loop_dev),
+ Err(e) => {
+ if begin.elapsed() > TIMEOUT {
+ return Err(e);
+ }
+ }
+ };
+ thread::sleep(INTERVAL);
+ }
+}
+
+#[cfg(not(target_os = "android"))]
+const LOOP_DEV_PREFIX: &str = "/dev/loop";
+
+#[cfg(target_os = "android")]
+const LOOP_DEV_PREFIX: &str = "/dev/block/loop";
+
+fn try_attach<P: AsRef<Path>>(
+ path: P,
+ offset: u64,
+ size_limit: u64,
+ direct_io: bool,
+) -> Result<PathBuf> {
+ // Get a free loop device
+ wait_for_path(LOOP_CONTROL)?;
+ let ctrl_file = OpenOptions::new()
+ .read(true)
+ .write(true)
+ .open(LOOP_CONTROL)
+ .context("Failed to open loop control")?;
+ let num = loop_ctl_get_free(&ctrl_file).context("Failed to get free loop device")?;
+
+ // Construct the loop_info64 struct
+ let backing_file = OpenOptions::new()
+ .read(true)
+ .custom_flags(if direct_io { O_DIRECT } else { 0 })
+ .open(&path)
+ .context(format!("failed to open {:?}", path.as_ref()))?;
+ // safe because the size of the array is the same as the size of the struct
+ let mut config: loop_config =
+ *DataInit::from_mut_slice(&mut [0; size_of::<loop_config>()]).unwrap();
+ config.fd = backing_file.as_raw_fd() as u32;
+ config.block_size = 4096;
+ config.info.lo_offset = offset;
+ config.info.lo_sizelimit = size_limit;
+ config.info.lo_flags = Flag::LO_FLAGS_READ_ONLY;
+ if direct_io {
+ config.info.lo_flags.insert(Flag::LO_FLAGS_DIRECT_IO);
+ }
+
+ // Configure the loop device to attach the backing file
+ let device_path = format!("{}{}", LOOP_DEV_PREFIX, num);
+ wait_for_path(&device_path)?;
+ let device_file = OpenOptions::new()
+ .read(true)
+ .write(true)
+ .open(&device_path)
+ .context(format!("failed to open {:?}", &device_path))?;
+ loop_configure(&device_file, &config)
+ .context(format!("Failed to configure {:?}", &device_path))?;
+
+ Ok(PathBuf::from(device_path))
+}
+
+/// Detaches backing file from the loop device `path`.
+pub fn detach<P: AsRef<Path>>(path: P) -> Result<()> {
+ let device_file = OpenOptions::new().read(true).write(true).open(&path)?;
+ loop_clr_fd(&device_file)?;
+ Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+ use super::*;
+ use std::fs;
+ use std::path::Path;
+
+ fn create_empty_file(path: &Path, size: u64) {
+ let f = File::create(path).unwrap();
+ f.set_len(size).unwrap();
+ }
+
+ fn is_direct_io(dev: &Path) -> bool {
+ let dio = Path::new("/sys/block").join(dev.file_name().unwrap()).join("loop/dio");
+ "1" == fs::read_to_string(&dio).unwrap().trim()
+ }
+
+ #[test]
+ fn attach_loop_device_with_dio() {
+ let a_dir = tempfile::TempDir::new().unwrap();
+ let a_file = a_dir.path().join("test");
+ let a_size = 4096u64;
+ create_empty_file(&a_file, a_size);
+ let dev = attach(a_file, 0, a_size, /*direct_io*/ true).unwrap();
+ scopeguard::defer! {
+ detach(&dev).unwrap();
+ }
+ assert!(is_direct_io(&dev));
+ }
+
+ #[test]
+ fn attach_loop_device_without_dio() {
+ let a_dir = tempfile::TempDir::new().unwrap();
+ let a_file = a_dir.path().join("test");
+ let a_size = 4096u64;
+ create_empty_file(&a_file, a_size);
+ let dev = attach(a_file, 0, a_size, /*direct_io*/ false).unwrap();
+ scopeguard::defer! {
+ detach(&dev).unwrap();
+ }
+ assert!(!is_direct_io(&dev));
+ }
+}