sys-util: introduce function to get device id

Introduce get_devid() to get major/minor number of a block device.

Signed-off-by: Liu Jiang <gerry@linux.alibaba.com>
Signed-off-by: Eryu Guan <eguan@linux.alibaba.com>

src/libs/sys-util-rs/src/device.rs

@@ -0,0 +1,110 @@
+// Copyright (c) 2019-2021 Alibaba Cloud
+// Copyright (c) 2019-2021 Ant Group
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+use std::fs;
+use std::io::Result;
+use std::path::PathBuf;
+
+use nix::sys::stat::{self, SFlag};
+
+use crate::{eother, sl};
+
+const SYS_DEV_BLOCK_PATH: &str = "/sys/dev/block";
+
+/// Get major and minor number of the device or of the device hosting the regular file/directory.
+pub fn get_devid(file: &str) -> Result<(u64, u64)> {
+    let fstat =
+        stat::stat(file).map_err(|e| eother!("get_devid: failed to stat {}: {:?}", file, e))?;
+
+    match SFlag::from_bits_truncate(fstat.st_mode) {
+        // For block device, check major/minor of the device special file itself
+        SFlag::S_IFBLK => Ok((
+            stat::major(fstat.st_rdev) as u64,
+            stat::minor(fstat.st_rdev) as u64,
+        )),
+        // For regular file, check major/minor of the underlying block device. Note that we need to
+        // get the major/minor of the real device not partition, e.g. /dev/sda not /dev/sda3
+        //
+        // We also accept dir here, as sandbox builtin storage is unlinked after open, and we only
+        // care about the underlying fs and block device, not the image file itself.
+        SFlag::S_IFREG | SFlag::S_IFDIR => get_real_devid(fstat.st_dev),
+        // Not block device, nor regular file, caller should handle this case.
+        _ => Ok((0, 0)),
+    }
+}
+
+/// Get the real device major/minor number for the device.
+///
+/// For example, given the dev_t of /dev/sda3 returns major and minor of /dev/sda. We rely on the
+/// fact that if /sys/dev/block/$major:$minor/partition exists, then it's a partition, and find its
+/// parent for the real device.
+fn get_real_devid(dev: nix::sys::stat::dev_t) -> Result<(u64, u64)> {
+    let major = stat::major(dev);
+    let minor = stat::minor(dev);
+    let mut real_dev_path = PathBuf::from(SYS_DEV_BLOCK_PATH)
+        .join(format!("{}:{}", major, minor))
+        .canonicalize()?;
+
+    // If 'partition' file exists, then it's a partition of the real device, take its parent.
+    // Otherwise it's already the real device.
+    loop {
+        if real_dev_path.join("partition").exists() {
+            real_dev_path = match real_dev_path.parent() {
+                Some(p) => p.to_path_buf(),
+                None => {
+                    return Err(eother!(
+                        "Can't find real device for dev {}:{}",
+                        major,
+                        minor
+                    ))
+                }
+            };
+            continue;
+        } else {
+            break;
+        }
+    }
+
+    // Parse major:minor in dev file
+    let dev_path = real_dev_path.join("dev");
+    let dev_buf = fs::read_to_string(&dev_path)?;
+    let dev_buf = dev_buf.trim_end();
+    debug!(
+        sl!(),
+        "get_real_devid: dev {}:{} -> {:?} ({})", major, minor, real_dev_path, dev_buf
+    );
+
+    let str_vec: Vec<&str> = dev_buf.split(':').collect();
+    match str_vec.len() {
+        2 => {
+            let major = str_vec[0]
+                .parse::<u64>()
+                .map_err(|_e| eother!("Failed to parse major number: {}", str_vec[0]))?;
+            let minor = str_vec[1]
+                .parse::<u64>()
+                .map_err(|_e| eother!("Failed to parse minor number: {}", str_vec[1]))?;
+            Ok((major, minor))
+        }
+        _ => {
+            return Err(eother!(
+                "Wrong format in {}: {}",
+                dev_path.to_string_lossy(),
+                dev_buf
+            ))
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_get_devid() {
+        get_devid("/proc/mounts").unwrap_err();
+        get_devid("/do/not/exist/file_______name").unwrap_err();
+    }
+}

src/libs/sys-util-rs/src/lib.rs

@@ -8,6 +8,7 @@ extern crate slog;
 
 pub mod cgroup;
 pub mod cpu;
+pub mod device;
 pub mod fs;
 pub mod mount;
 pub mod numa;