Document the mount.linux module

Also, deprecate a few flags that should not be used by userland.

Author: asomers

src/mount/linux.rs

@@ -1,9 +1,9 @@
-#![allow(missing_docs)]
 use crate::errno::Errno;
 use crate::{NixPath, Result};
 use libc::{self, c_int, c_ulong};
 
 libc_bitflags!(
+    /// Used with [`mount`].
     pub struct MsFlags: c_ulong {
         /// Mount read-only
         MS_RDONLY;
@@ -27,36 +27,80 @@ libc_bitflags!(
         MS_NODIRATIME;
         /// Linux 2.4.0 - Bind directory at different place
         MS_BIND;
+        /// Move an existing mount to a new location
         MS_MOVE;
+        /// Used to create a recursive bind mount.
         MS_REC;
+        /// Suppress the display of certain kernel warning messages.
         MS_SILENT;
+        /// VFS does not apply the umask
         MS_POSIXACL;
+        /// The resulting mount cannot subsequently be bind mounted.
         MS_UNBINDABLE;
+        /// Make this mount point private.
         MS_PRIVATE;
+        /// If this is a shared mount point that is a member of a peer group
+        /// that  contains  other  members, convert it to a slave mount.
         MS_SLAVE;
+        /// Make  this mount point shared.
         MS_SHARED;
+        /// When a file on this filesystem is accessed,  update  the  file's
+        /// last  access  time (atime) only if the current value of atime is
+        /// less than or equal to the file's last modification time  (mtime) or
+        /// last  status change time (ctime).
         MS_RELATIME;
+        /// Mount request came from within the kernel
+        #[deprecated(since = "0.27.0", note = "Should only be used in-kernel")]
         MS_KERNMOUNT;
+        /// Update inode I_version field
         MS_I_VERSION;
+        /// Always  update  the  last access time (atime) when files on this
+        /// filesystem are accessed.
         MS_STRICTATIME;
+        /// Reduce on-disk updates of inode timestamps (atime, mtime, ctime) by
+        /// maintaining these changes only in memory.
         MS_LAZYTIME;
+        #[deprecated(since = "0.27.0", note = "Should only be used in-kernel")]
+        #[allow(missing_docs)]  // Not documented in Linux
         MS_ACTIVE;
+        #[deprecated(since = "0.27.0", note = "Should only be used in-kernel")]
+        #[allow(missing_docs)]  // Not documented in Linux
         MS_NOUSER;
+        #[allow(missing_docs)]  // Not documented in Linux; possibly kernel-only
         MS_RMT_MASK;
+        #[allow(missing_docs)]  // Not documented in Linux; possibly kernel-only
         MS_MGC_VAL;
+        #[allow(missing_docs)]  // Not documented in Linux; possibly kernel-only
         MS_MGC_MSK;
     }
 );
 
 libc_bitflags!(
+    /// Used with [`umount2].
     pub struct MntFlags: c_int {
+        /// Attempt to unmount even if still in use, aborting pending requests.
         MNT_FORCE;
+        /// Lazy unmount.  Disconnect the file system immediately, but don't
+        /// actually unmount it until it ceases to be busy.
         MNT_DETACH;
+        /// Mark the mount point as expired.
         MNT_EXPIRE;
+        /// Don't dereference `target` if it is a symlink.  
         UMOUNT_NOFOLLOW;
     }
 );
 
+/// Mount a file system.
+///
+/// # Arguments
+/// - `source`  -   Specifies the file system.  e.g. `/dev/sd0`.
+/// - `target` -    Specifies the destination.  e.g. `/mnt`.
+/// - `fstype` -    The file system type, e.g. `ext4`.
+/// - `flags` -     Optional flags controlling the mount.
+/// - `data` -      Optional file system specific data.
+///
+/// # See Also
+/// [`mount`](https://man7.org/linux/man-pages/man2/mount.2.html)
 pub fn mount<
     P1: ?Sized + NixPath,
     P2: ?Sized + NixPath,
@@ -99,13 +143,17 @@ pub fn mount<
     Errno::result(res).map(drop)
 }
 
+/// Unmount the file system mounted at `target`.
 pub fn umount<P: ?Sized + NixPath>(target: &P) -> Result<()> {
     let res =
         target.with_nix_path(|cstr| unsafe { libc::umount(cstr.as_ptr()) })?;
 
     Errno::result(res).map(drop)
 }
 
+/// Unmount the file system mounted at `target`.
+///
+/// See also [`umount`](https://man7.org/linux/man-pages/man2/umount.2.html)
 pub fn umount2<P: ?Sized + NixPath>(target: &P, flags: MntFlags) -> Result<()> {
     let res = target.with_nix_path(|cstr| unsafe {
         libc::umount2(cstr.as_ptr(), flags.bits)