Add a Statfs::flags method

It returns the mount flags on the BSDs.  On Linux, it returns a slightly
different set of flags.

CHANGELOG.md

@@ -6,6 +6,8 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 ## [Unreleased] - ReleaseDate
 ### Added
 
+- Added a 'Statfs::flags' method.
+  ([#1849](https://github.com/nix-rust/nix/pull/1849))
 - Added `NSFS_MAGIC` FsType on Linux and Android.
   ([#1829](https://github.com/nix-rust/nix/pull/1829))
 - Added `sched_getcpu` on platforms that support it.

src/sys/statfs.rs

@@ -10,6 +10,14 @@ use std::ffi::CStr;
 use cfg_if::cfg_if;
 
 use crate::{NixPath, Result, errno::Errno};
+#[cfg(any(target_os = "dragonfly",
+          target_os = "freebsd",
+          target_os = "macos",
+          target_os = "netbsd",
+          target_os = "openbsd"))]
+use crate::mount::MntFlags;
+#[cfg(target_os = "linux")]
+use crate::sys::statvfs::FsFlags;
 
 /// Identifies a mounted file system
 #[cfg(target_os = "android")]
@@ -374,6 +382,26 @@ impl Statfs {
         self.0.f_bsize
     }
 
+    /// Get the mount flags
+    #[cfg(any(target_os = "dragonfly",
+              target_os = "freebsd",
+              target_os = "macos",
+              target_os = "netbsd",
+              target_os = "openbsd"))]
+    #[cfg_attr(docsrs, doc(cfg(all())))]
+    pub fn flags(&self) -> MntFlags {
+        MntFlags::from_bits_truncate(self.0.f_flags as i32)
+    }
+
+    /// Get the mount flags
+    // The f_flags field exists on Android and Fuchsia too, but without man
+    // pages I can't tell if it can be cast to FsFlags.
+    #[cfg(target_os = "linux")]
+    #[cfg_attr(docsrs, doc(cfg(all())))]
+    pub fn flags(&self) -> FsFlags {
+        FsFlags::from_bits_truncate(self.0.f_flags as libc::c_ulong)
+    }
+
     /// Maximum length of filenames
     #[cfg(any(target_os = "freebsd", target_os = "openbsd"))]
     #[cfg_attr(docsrs, doc(cfg(all())))]
@@ -641,16 +669,24 @@ impl Statfs {
 
 impl Debug for Statfs {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        f.debug_struct("Statfs")
-            .field("optimal_transfer_size", &self.optimal_transfer_size())
-            .field("block_size", &self.block_size())
-            .field("blocks", &self.blocks())
-            .field("blocks_free", &self.blocks_free())
-            .field("blocks_available", &self.blocks_available())
-            .field("files", &self.files())
-            .field("files_free", &self.files_free())
-            .field("filesystem_id", &self.filesystem_id())
-            .finish()
+        let mut ds = f.debug_struct("Statfs");
+        ds.field("optimal_transfer_size", &self.optimal_transfer_size());
+        ds.field("block_size", &self.block_size());
+        ds.field("blocks", &self.blocks());
+        ds.field("blocks_free", &self.blocks_free());
+        ds.field("blocks_available", &self.blocks_available());
+        ds.field("files", &self.files());
+        ds.field("files_free", &self.files_free());
+        ds.field("filesystem_id", &self.filesystem_id());
+        #[cfg(any(target_os = "dragonfly",
+                  target_os = "freebsd",
+                  target_os = "macos",
+                  target_os = "linux",
+                  target_os = "netbsd",
+                  target_os = "openbsd"))]
+        ds.field("flags", &self.flags());
+        ds.finish()
+
     }
 }