Implement findmnt

Cargo.toml

@@ -29,6 +29,7 @@ feat_common_core = [
   "blockdev",
   "ctrlaltdel",
   "dmesg",
+  "findmnt",
   "fsfreeze",
   "last",
   "lscpu",
@@ -38,6 +39,9 @@ feat_common_core = [
   "setsid",
 ]
 
+[workspace]
+members = ["src/uu/findmnt"]
+
 [workspace.dependencies]
 clap = { version = "4.4", features = ["wrap_help", "cargo"] }
 clap_complete = "4.4"
@@ -73,6 +77,7 @@ uucore = { workspace = true }
 blockdev = { optional = true, version = "0.0.1", package = "uu_blockdev", path = "src/uu/blockdev" }
 ctrlaltdel = { optional = true, version = "0.0.1", package = "uu_ctrlaltdel", path = "src/uu/ctrlaltdel" }
 dmesg = { optional = true, version = "0.0.1", package = "uu_dmesg", path = "src/uu/dmesg" }
+findmnt = { optional = true, version = "0.0.1", package = "uu_findmnt", path = "src/uu/findmnt" }
 fsfreeze = { optional = true, version = "0.0.1", package = "uu_fsfreeze", path = "src/uu/fsfreeze" }
 last = { optional = true, version = "0.0.1", package = "uu_last", path = "src/uu/last" }
 lscpu = { optional = true, version = "0.0.1", package = "uu_lscpu", path = "src/uu/lscpu" }

src/uu/findmnt/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "uu_findmnt"
+version = "0.0.1"
+edition = "2021"
+
+[lib]
+path = "src/findmnt.rs"
+
+[[bin]]
+name = "findmnt"
+path = "src/main.rs"
+
+[dependencies]
+uucore = { workspace = true }
+clap = { workspace = true }
+serde = { workspace = true }
+serde_json = { workspace = true }

src/uu/findmnt/findmnt.md

@@ -0,0 +1,7 @@
+# findmnt
+
+```
+findmnt [OPTION]...
+```
+
+display information about mounted filesystems

src/uu/findmnt/src/findmnt.rs

@@ -0,0 +1,302 @@
+// This file is part of the uutils util-linux package.
+//
+// For the full copyright and license information, please view the LICENSE
+// file that was distributed with this source code.
+
+use std::{collections::HashMap, fs, string};
+
+use clap::{crate_version, Arg, ArgAction, Command};
+use serde::Serialize;
+use uucore::{error::UResult, format_usage, help_about, help_usage};
+
+// Flat mount information structure as described in:
+// https://www.man7.org/linux/man-pages/man5/proc_pid_mountinfo.5.html
+#[derive(Debug)]
+struct MountEntry {
+    id: usize,
+    parent_id: usize,
+    _root: String,
+    target: String,
+    source: String,
+    options: String,
+    fstype: String,
+}
+
+impl MountEntry {
+    // Parses a line from `/proc/self/mountinfo`, which follows the format described under proc_pid_mountinfo(5)
+    // We ignore some of the fields as they are not relevant for the purposes of findmnt
+    fn parse(input: &str) -> Self {
+        let mut parts = input.trim().split(" ");
+
+        let id = parts
+            .next()
+            .unwrap()
+            .parse::<usize>()
+            .expect("Could not parse Mount ID");
+        let parent_id = parts
+            .next()
+            .unwrap()
+            .parse::<usize>()
+            .expect("Could not parse Parent ID");
+        parts.next(); // Skip field 3
+
+        let root = parts.next().unwrap().to_string();
+        let target = parts.next().unwrap().to_string();
+        let options = parts.next().unwrap().to_string();
+
+        // Field 7 is a variable-length list of space-separated optional values, it's end is marked by a `-` separator
+        // Skip everything until the separator, and the separator itself
+        let mut parts = parts.skip_while(|s| *s != "-").skip(1);
+
+        let fstype = parts.next().unwrap().to_string();
+        let source = parts.next().unwrap().to_string();
+
+        // Ignore the rest
+
+        Self {
+            id,
+            parent_id,
+            _root: root,
+            source,
+            target,
+            fstype,
+            options,
+        }
+    }
+}
+
+// Data structures used for the final output
+#[derive(Debug, Serialize)]
+struct MountData {
+    filesystems: Vec<Mount>,
+}
+
+#[derive(Debug, Serialize, Clone)]
+struct Mount {
+    target: String,
+    source: String,
+    fstype: String,
+    options: String,
+
+    #[serde(skip_serializing_if = "Vec::is_empty")]
+    children: Vec<Mount>,
+}
+
+impl Mount {
+    fn get_value(&self, field: &Column) -> String {
+        match field {
+            Column::FsRoot => todo!(),
+            Column::FsType => self.fstype.clone(),
+            Column::FsOptions => todo!(),
+            Column::Id => todo!(),
+            Column::Options => self.options.clone(),
+            Column::Parent => todo!(),
+            Column::Source => self.source.clone(),
+            Column::Target => self.target.clone(),
+        }
+    }
+}
+
+fn read_mounts() -> Vec<Mount> {
+    let content =
+        fs::read_to_string("/proc/self/mountinfo").expect("Could not read /proc/self/mountinfo");
+    let mount_entries: HashMap<_, _> = content
+        .lines()
+        .map(MountEntry::parse)
+        .map(|me| (me.id, me))
+        .collect();
+
+    // Very odd if this happens but technically possible
+    if mount_entries.is_empty() {
+        return vec![];
+    }
+
+    // Try finding the "proper" root mounts, ie. ones were id == parent_id
+    let mut root_mounts: Vec<_> = mount_entries
+        .iter()
+        .filter(|(_, e)| e.parent_id == e.id)
+        .map(|(_, e)| e)
+        .collect();
+
+    // In many cases there will be no "proper" roots, so just use the mount with the lowest parent_id
+    if root_mounts.is_empty() {
+        let root_entry = mount_entries
+            .iter()
+            .min_by_key(|(_, e)| e.parent_id)
+            .unwrap()
+            .1;
+        root_mounts.push(root_entry)
+    }
+
+    fn with_children(m: &MountEntry, haystack: &HashMap<usize, MountEntry>) -> Mount {
+        let child_entries: Vec<&MountEntry> = haystack
+            .iter()
+            .filter(|(_, e)| e.parent_id == m.id)
+            .map(|(_, e)| e)
+            .collect();
+
+        // TODO: Use iterator
+        let mut children: Vec<Mount> = vec![];
+        for entry in child_entries {
+            children.push(with_children(entry, haystack));
+        }
+
+        Mount {
+            target: m.target.clone(),
+            source: m.source.clone(),
+            fstype: m.fstype.clone(),
+            options: m.options.clone(),
+            children,
+        }
+    }
+
+    root_mounts
+        .iter()
+        .map(|e| with_children(e, &mount_entries))
+        .collect()
+}
+
+// TODO: Add the remaining columns supported by `findmnt`
+#[derive(Debug, Clone)]
+enum Column {
+    FsRoot,
+    FsType,
+    FsOptions,
+    Id,
+    Options,
+    Parent,
+    Source,
+    Target,
+}
+
+impl Column {
+    fn header_text(&self) -> &'static str {
+        match self {
+            Column::FsRoot => "FSROOT",
+            Column::FsType => "FSTYPE",
+            Column::FsOptions => "FS-OPTIONS",
+            Column::Id => "ID",
+            Column::Options => "OPTIONS",
+            Column::Parent => "PARENT",
+            Column::Source => "SOURCE",
+            Column::Target => "TARGET",
+        }
+    }
+
+    fn header_width(&self) -> usize {
+        self.header_text().len()
+    }
+}
+
+const DEFAULT_COLS: &[Column] = &[
+    Column::Target,
+    Column::Source,
+    Column::FsType,
+    Column::Options,
+];
+
+struct OutputOptions {
+    json: bool,
+    cols: Vec<Column>,
+}
+
+fn get_column_widths(cols: &Vec<Column>, rows: &Vec<Mount>) -> Vec<usize> {
+    // Initialize max_widths with the width of the column headers
+    let mut max_widths: Vec<_> = cols.iter().map(|col| col.header_width()).collect();
+
+    // Go through all table rows, and check if any values are wider than the header text
+    // Set that as the new max_width for that column
+    for row in rows {
+        for (i, col) in cols.iter().enumerate() {
+            let value_width = row.get_value(col).len();
+            max_widths[i] = max_widths[i].max(value_width);
+        }
+    }
+
+    max_widths
+}
+
+fn print_output(fs: MountData, options: OutputOptions) {
+    if options.json {
+        let json = serde_json::to_string_pretty(&fs).unwrap();
+        println!("{}", json);
+        return;
+    }
+
+    // Before printing, the mount tree needs to be flatten into a single vector of rows
+    let mut flattened_mounts: Vec<Mount> = vec![];
+
+    fn flatten(mnt: &Mount, acc: &mut Vec<Mount>) {
+        acc.push(mnt.clone());
+        for child in &mnt.children {
+            flatten(&child, acc);
+        }
+    }
+
+    for rootfs in &fs.filesystems {
+        flatten(rootfs, &mut flattened_mounts);
+    }
+
+    let col_widths = get_column_widths(&options.cols, &flattened_mounts);
+
+    // Print headers
+    let headers: Vec<_> = options
+        .cols
+        .iter()
+        .enumerate()
+        .map(|(i, col)| format!("{:<width$}", col.header_text(), width = col_widths[i]))
+        .collect();
+    println!("{}", headers.join(" "));
+
+    for row in flattened_mounts {
+        let values: Vec<_> = options
+            .cols
+            .iter()
+            .enumerate()
+            .map(|(i, col)| format!("{:<width$}", row.get_value(col), width = col_widths[i]))
+            .collect();
+        println!("{}", values.join(" "));
+    }
+}
+
+#[uucore::main]
+pub fn uumain(args: impl uucore::Args) -> UResult<()> {
+    let matches: clap::ArgMatches = uu_app().try_get_matches_from(args)?;
+
+    let output_opts = OutputOptions {
+        json: matches.get_flag(options::JSON),
+
+        // TODO: Use arguments to control which cols are printed out
+        cols: Vec::from(DEFAULT_COLS),
+    };
+
+    let fs = MountData {
+        filesystems: read_mounts(),
+    };
+
+    print_output(fs, output_opts);
+
+    Ok(())
+}
+
+const ABOUT: &str = help_about!("findmnt.md");
+const USAGE: &str = help_usage!("findmnt.md");
+
+mod options {
+    pub const JSON: &str = "json";
+}
+
+pub fn uu_app() -> Command {
+    Command::new(uucore::util_name())
+        .version(crate_version!())
+        .about(ABOUT)
+        .override_usage(format_usage(USAGE))
+        .infer_long_args(true)
+        .arg(
+            Arg::new(options::JSON)
+                .short('J')
+                .long("json")
+                .help("Use JSON output format")
+                .action(ArgAction::SetTrue),
+        )
+}

src/uu/findmnt/src/main.rs

@@ -0,0 +1 @@
+uucore::bin!(uu_findmnt);