bind.rs

use std::fmt;
use std::ffi::{CStr, CString, OsStr};
use std::os::unix::ffi::OsStrExt;
use std::path::Path;

use nix::mount::{MsFlags, mount};

use crate::{OSError, Error};
use crate::util::{path_to_cstring, as_path};
use crate::explain::{Explainable, exists, user};
use crate::remount::Remount;


/// A mount bind definition
///
/// By default bind mount is recursive (it's what you want most of the time).
///
/// Also recursive mounts can be used in user namespaces.
#[derive(Debug, Clone)]
pub struct BindMount {
    source: CString,
    target: CString,
    recursive: bool,
    readonly: bool,
}

impl BindMount {
    /// Create a new, recursive bind mount
    ///
    /// You can disable recursion with a `non_recursive()` method
    pub fn new<A: AsRef<Path>, B: AsRef<Path>>(source: A, target: B)
        -> BindMount
    {
        BindMount {
            source: path_to_cstring(source.as_ref()),
            target: path_to_cstring(target.as_ref()),
            recursive: true,
            readonly: false,
        }
    }
    /// Toggle recursion
    pub fn recursive(mut self, flag: bool) -> BindMount {
        self.recursive = flag;
        self
    }
    /// If set to `true` makes bind-mount readonly
    ///
    /// Few notes:
    ///
    /// 1. This makes additional `mount` call (`Remount().readonly()`)
    /// 2. If remount fails mount bind is left on the filesystem, no cleanup
    ///    is done
    /// 3. If set to `false` is option is no-op (does **not** remount `rw`)
    pub fn readonly(mut self, flag: bool) -> BindMount {
        self.readonly = flag;
        self
    }

    /// Execute a bind mount
    pub fn bare_mount(self) -> Result<(), OSError> {
        let mut flags = MsFlags::MS_BIND;
        if self.recursive {
            flags |= MsFlags::MS_REC;
        }
        if let Err(err) = mount(
            Some(&*self.source),
            &*self.target,
            None::<&CStr>,
            flags,
            None::<&CStr>,
        ) {
            return Err(OSError::from_nix(err, Box::new(self)));
        }
        if self.readonly {
            Remount::new(OsStr::from_bytes(self.target.as_bytes()))
                .bind(true)
                .readonly(true)
                .bare_remount()?;
        }
        Ok(())
    }

    /// Execute a bind mount and explain the error immediately
    pub fn mount(self) -> Result<(), Error> {
        self.bare_mount().map_err(OSError::explain)
    }
}

impl fmt::Display for BindMount {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        if self.recursive {
            write!(fmt, "recursive ")?;
        }
        write!(fmt, "bind mount {:?} -> {:?}",
            as_path(&self.source), as_path(&self.target))
    }
}

impl Explainable for BindMount {
    fn explain(&self) -> String {
        [
            format!("source: {}", exists(as_path(&self.source))),
            format!("target: {}", exists(as_path(&self.target))),
            user().to_string(),
        ].join(", ")
    }
}