fsfreeze: Add tool

Add fsfreeze, a Linux-specific tool used to freeze/thaw writes to a
filesystem. It's an extremely simple tool so this should have full
feature-parity.

src/uu/fsfreeze/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "uu_fsfreeze"
+version = "0.0.1"
+edition = "2021"
+
+[lib]
+path = "src/fsfreeze.rs"
+
+[[bin]]
+name = "fsfreeze"
+path = "src/main.rs"
+
+[dependencies]
+clap = { workspace = true }
+linux-raw-sys = { workspace = true }
+regex = { workspace = true }
+sysinfo = { workspace = true }
+uucore = { workspace = true }

src/uu/fsfreeze/fsfreeze.md

@@ -0,0 +1,7 @@
+# fsfreeze
+
+```
+fsfreeze <--freeze|--unfreeze> <MOUNTPOINT>
+```
+
+suspends or resumes modifications to a mounted filesystem

src/uu/fsfreeze/src/fsfreeze.rs

@@ -0,0 +1,85 @@
+// 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 clap::{crate_version, Arg, ArgAction, ArgGroup, Command};
+#[cfg(target_os = "linux")]
+use std::{fs::File, io, os::fd::AsRawFd};
+#[cfg(target_os = "linux")]
+use uucore::{error::UIoError, libc};
+use uucore::{error::UResult, format_usage, help_about, help_usage};
+
+const ABOUT: &str = help_about!("fsfreeze.md");
+const USAGE: &str = help_usage!("fsfreeze.md");
+
+#[cfg(target_os = "linux")]
+#[uucore::main]
+pub fn uumain(args: impl uucore::Args) -> UResult<()> {
+    let matches: clap::ArgMatches = uu_app().try_get_matches_from(args)?;
+    let mountpoint = matches.get_one::<String>("mountpoint").unwrap();
+    let file = File::open(mountpoint)?;
+    let metadata = file.metadata()?;
+    if !metadata.is_dir() {
+        return Err(UIoError::new(io::ErrorKind::InvalidData, "not a directory"));
+    }
+
+    let (op_name, op_code) = if matches.get_flag("freeze") {
+        ("freeze", linux_raw_sys::ioctl::FIFREEZE)
+    } else {
+        ("unfreeze", linux_raw_sys::ioctl::FITHAW)
+    };
+
+    if unsafe { libc::ioctl(file.as_raw_fd(), op_code.into(), 0) } < 0 {
+        uucore::show_error!(
+            "failed to {} the filesystem: {}",
+            op_name,
+            UIoError::from(io::Error::last_os_error())
+        );
+    }
+    Ok(())
+}
+
+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("freeze")
+                .short('f')
+                .long("freeze")
+                .help("freeze the filesystem")
+                .action(ArgAction::SetTrue),
+        )
+        .arg(
+            Arg::new("unfreeze")
+                .short('u')
+                .long("unfreeze")
+                .help("unfreeze the filesystem")
+                .action(ArgAction::SetTrue),
+        )
+        .arg(
+            Arg::new("mountpoint")
+                .help("mountpoint of the filesystem")
+                .required(true)
+                .action(ArgAction::Set),
+        )
+        .group(
+            ArgGroup::new("action")
+                .required(true)
+                .args(["freeze", "unfreeze"]),
+        )
+}
+
+#[cfg(not(target_os = "linux"))]
+#[uucore::main]
+pub fn uumain(args: impl uucore::Args) -> UResult<()> {
+    let _matches: clap::ArgMatches = uu_app().try_get_matches_from(args)?;
+
+    Err(uucore::error::USimpleError::new(
+        1,
+        "`fsfreeze` is available only on Linux.",
+    ))
+}

src/uu/fsfreeze/src/main.rs

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