fix: gate posix_fallocate to Linux OS

`posix_fallocate` is not available on Mac.

Author: austinhartzheim

src/utils.rs

@@ -1,18 +1,18 @@
 use std::fs::File;
 use std::io;
-#[cfg(unix)]
+#[cfg(target_os = "linux")]
 use std::os::fd::AsRawFd;
 
 /// Set the length of the file to the specified length.
 pub(crate) fn set_len(file: &File, len: i64) -> Result<(), io::Error> {
-    // On Unix platforms, `.set_len()` may not return an error of the disk is full, so we allocate
+    // On Linux platforms, `.set_len()` may not return an error of the disk is full, so we allocate
     // the entire file to ensure space is available.
-    #[cfg(unix)]
+    #[cfg(target_os = "linux")]
     match unsafe { libc::posix_fallocate(file.as_raw_fd(), 0, len) } {
         0 => Ok(()),
         err => Err(io::Error::from_raw_os_error(err)),
     }
     // Support for non-Linux platforms is best-effort.
-    #[cfg(not(unix))]
-    data_file.set_len(STATE_SIZE).map_err(FailedStateRead)
+    #[cfg(not(target_os = "linux"))]
+    file.set_len(leng).map_err(FailedStateRead)
 }