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

@@ -0,0 +1,104 @@
+// 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::os::unix::fs::{FileTypeExt, MetadataExt};
+use std::path::{Path, PathBuf};
+
+use nix::sys::stat;
+
+use crate::{eother, sl};
+
+const SYS_DEV_BLOCK_PATH: &str = "/sys/dev/block";
+const BLKDEV_PARTITION: &str = "partition";
+const BLKDEV_DEV_FILE: &str = "dev";
+
+/// Get major and minor number of the device or of the device hosting the regular file/directory.
+pub fn get_devid_for_blkio_cgroup<P: AsRef<Path>>(path: P) -> Result<Option<(u64, u64)>> {
+    let md = fs::metadata(path)?;
+
+    if md.is_dir() || md.is_file() {
+        // For regular file/directory, get major/minor of the block device hosting it.
+        // Note that we need to get the major/minor of the block device instead of partition,
+        // e.g. /dev/sda instead of /dev/sda3, because blkio cgroup works with block major/minor.
+        let id = md.dev();
+        Ok(Some((stat::major(id), stat::minor(id))))
+    } else if md.file_type().is_block_device() {
+        // For block device, get major/minor of the device special file itself
+        get_block_device_id(md.rdev())
+    } else {
+        Ok(None)
+    }
+}
+
+/// Get the block device major/minor number from a partition/block device(itself).
+///
+/// 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_block_device_id(dev: stat::dev_t) -> Result<Option<(u64, u64)>> {
+    let major = stat::major(dev);
+    let minor = stat::minor(dev);
+    let mut blk_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 !blk_dev_path.join(BLKDEV_PARTITION).exists() {
+            break;
+        }
+        blk_dev_path = match blk_dev_path.parent() {
+            Some(p) => p.to_path_buf(),
+            None => {
+                return Err(eother!(
+                    "Can't find real device for dev {}:{}",
+                    major,
+                    minor
+                ))
+            }
+        };
+    }
+
+    // Parse major:minor in dev file
+    let dev_path = blk_dev_path.join(BLKDEV_DEV_FILE);
+    let dev_buf = fs::read_to_string(&dev_path)?;
+    let dev_buf = dev_buf.trim_end();
+    debug!(
+        sl!(),
+        "get_real_devid: dev {}:{} -> {:?} ({})", major, minor, blk_dev_path, dev_buf
+    );
+
+    if let Some((major, minor)) = dev_buf.split_once(':') {
+        let major = major
+            .parse::<u64>()
+            .map_err(|_e| eother!("Failed to parse major number: {}", major))?;
+        let minor = minor
+            .parse::<u64>()
+            .map_err(|_e| eother!("Failed to parse minor number: {}", minor))?;
+        Ok(Some((major, minor)))
+    } else {
+        Err(eother!(
+            "Wrong format in {}: {}",
+            dev_path.to_string_lossy(),
+            dev_buf
+        ))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_get_devid() {
+        //let (major, minor) = get_devid_for_blkio_cgroup("/dev/vda1").unwrap().unwrap();
+        assert!(get_devid_for_blkio_cgroup("/dev/tty").unwrap().is_none());
+        get_devid_for_blkio_cgroup("/do/not/exist/file_______name").unwrap_err();
+    }
+}

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

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