[pve-devel] [PATCH installer 4/5] chroot: replace btrfs parsing regex with lsblk json parsing

[Christoph Heiss]

Makes the whole routine a lot more robust by parsing the JSON output of
`lsblk` instead of the human-readable output from `btrfs filesystem
show`.

The labels of Btrfs filesystems are pretty much arbitrary labels, e.g.
the following is a valid filesystem and thus output from `btrfs
filesystem show`:

Label: 'uuid: 70361d98-7492-45d4-a0e4-bf8fee9203a3'  uuid: ab158685-c0b7-4540-a739-72c43a773282
        Total devices 1 FS bytes used 144.00KiB
        devid    1 size 8.00GiB used 536.00MiB path /dev/sda

.. which would break the current parsing code.

Also drops the usage of a regex, thus being able to eliminate the whole
regex machinery from the final binary. This reduces (stripped) binary
size significantly, from 2.4 MiB to ~727 KiB, a ~70%(!) decrease.

   text	   data	    bss	    dec	    hex	filename
2213016	 261208	    408	2474632	 25c288	proxmox-chroot-old
 702481	  27776	    360	 730617	  b25f9	proxmox-chroot-new

No functional changes.

Signed-off-by: Christoph Heiss <c.heiss at proxmox.com>
---
 proxmox-chroot/Cargo.toml  |  2 +-
 proxmox-chroot/src/main.rs | 48 +++++++++++++++++++++++++++-----------
 2 files changed, 35 insertions(+), 15 deletions(-)

diff --git a/proxmox-chroot/Cargo.toml b/proxmox-chroot/Cargo.toml
index c043938..a6a705d 100644
--- a/proxmox-chroot/Cargo.toml
+++ b/proxmox-chroot/Cargo.toml
@@ -9,6 +9,6 @@ homepage = "https://www.proxmox.com"
 
 [dependencies]
 anyhow.workspace = true
-regex.workspace = true
 proxmox-installer-common = { workspace = true, features = [ "cli" ] }
+serde = { workspace = true, features = [ "derive" ] }
 serde_json.workspace = true
diff --git a/proxmox-chroot/src/main.rs b/proxmox-chroot/src/main.rs
index 037f079..2cff630 100644
--- a/proxmox-chroot/src/main.rs
+++ b/proxmox-chroot/src/main.rs
@@ -18,7 +18,7 @@ use proxmox_installer_common::{
     options::FsType,
     setup::{InstallConfig, SetupInfo},
 };
-use regex::Regex;
+use serde::Deserialize;
 
 const ANSWER_MP: &str = "answer";
 static BINDMOUNTS: [&str; 4] = ["dev", "proc", "run", "sys"];
@@ -355,29 +355,49 @@ fn mount_btrfs(btrfs_uuid: Option<String>) -> Result<()> {
     Ok(())
 }
 
+/// Searches for all Btrfs filesystems present on the system.
+///
+/// # Returns
+///
+/// The UUID of that filesystem, if a single Btrfs filesystem is found.
+/// If multiple are found, returns a (human-readable) error with all possible
+/// filesystem UUIDs.
 fn get_btrfs_uuid() -> Result<String> {
-    let output = Command::new("btrfs")
-        .arg("filesystem")
-        .arg("show")
+    let output = Command::new("lsblk")
+        .args(["--json", "--fs", "--list", "--output", "fstype,uuid"])
         .output()?;
+
     if !output.status.success() {
         bail!(
             "Error checking for BTRFS file systems: {}",
             String::from_utf8(output.stderr)?
         );
     }
-    let out = String::from_utf8(output.stdout)?;
-    let mut uuids = Vec::new();
 
-    let re_uuid =
-        Regex::new(r"uuid: ([0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12})$")?;
-    for line in out.lines() {
-        if let Some(cap) = re_uuid.captures(line) {
-            if let Some(uuid) = cap.get(1) {
-                uuids.push(uuid.as_str());
-            }
-        }
+    #[derive(Deserialize)]
+    struct Entry {
+        fstype: Option<String>,
+        uuid: Option<String>,
     }
+
+    #[derive(Deserialize)]
+    struct LsblkOutput {
+        blockdevices: Vec<Entry>,
+    }
+
+    let out: LsblkOutput = serde_json::from_slice(&output.stdout)?;
+    let uuids = out
+        .blockdevices
+        .iter()
+        .filter_map(|entry| match entry {
+            Entry {
+                fstype: Some(fstype),
+                uuid: Some(uuid),
+            } if fstype == "btrfs" => Some(uuid),
+            _ => None,
+        })
+        .collect::<Vec<&String>>();
+
     match uuids.len() {
         0 => bail!("Could not find any BTRFS UUID"),
         i if i > 1 => {
-- 
2.49.0