chore: rid of fs2

fs2 was introduced in PR #500, but we actually don't really need that
much from it. This commit removes the extra dependency in favor of doing
the same directly. I think this is pretty-much equivalent to inlining
the code.

nomt/Cargo.toml

@@ -29,7 +29,6 @@ lru = "0.12.3"
 libc = "0.2.155"
 criterion = { version = "0.3", optional = true }
 thread_local = "1.1.8"
-fs2 = "0.4.3"
 cfg-if = "1.0.0"
 
 [target.'cfg(target_os="linux")'.dependencies]

nomt/src/store/flock.rs

@@ -5,8 +5,6 @@ use std::{
     path::Path,
 };
 
-use fs2::FileExt as _;
-
 /// Represents a cross-platform advisory lock on a directory.
 pub struct Flock {
     lock_fd: File,
@@ -22,19 +20,18 @@ impl Flock {
             .create(true)
             .open(lock_path)?;
 
-        match lock_fd.try_lock_exclusive() {
+        match crate::sys::unix::try_lock_exclusive(&lock_fd) {
             Ok(_) => Ok(Self { lock_fd }),
-            Err(_) => {
-                let err = fs2::lock_contended_error();
-                anyhow::bail!("Failed to lock directory: {err}");
+            Err(e) => {
+                anyhow::bail!("Failed to lock directory: {e}");
             }
         }
     }
 }
 
 impl Drop for Flock {
     fn drop(&mut self) {
-        if let Err(e) = self.lock_fd.unlock() {
+        if let Err(e) = crate::sys::unix::unlock(&self.lock_fd) {
             eprintln!("Failed to unlock directory lock: {e}");
         }
     }

nomt/src/sys/unix.rs

@@ -1,2 +1,23 @@
 //! Common Unix definitions.
 
+use std::{fs::File, os::fd::AsRawFd as _};
+
+pub fn try_lock_exclusive(file: &File) -> std::io::Result<()> {
+    unsafe {
+        if libc::flock(file.as_raw_fd(), libc::LOCK_EX | libc::LOCK_NB) == -1 {
+            Err(std::io::Error::last_os_error())
+        } else {
+            Ok(())
+        }
+    }
+}
+
+pub fn unlock(file: &File) -> std::io::Result<()> {
+    unsafe {
+        if libc::flock(file.as_raw_fd(), libc::LOCK_UN) == -1 {
+            Err(std::io::Error::last_os_error())
+        } else {
+            Ok(())
+        }
+    }
+}