linux-support 0.0.25

Comprehensive Linux support for namespaces, cgroups, processes, scheduling, parsing /proc, parsing /sys, signals, hyper threads, CPUS, NUMA nodes, unusual file descriptors, PCI devices and much, much more
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// This file is part of linux-support. It is subject to the license terms in the COPYRIGHT file found in the top-level directory of this distribution and at https://raw.githubusercontent.com/lemonrock/linux-support/master/COPYRIGHT. No part of linux-support, including this file, may be copied, modified, propagated, or distributed except according to the terms contained in the COPYRIGHT file.
// Copyright © 2020 The developers of linux-support. See the COPYRIGHT file in the top-level directory of this distribution and at https://raw.githubusercontent.com/lemonrock/linux-support/master/COPYRIGHT.


/// Per open file description leasing.
///
/// Leases are relinquished when all open file descriptors for a file are closed.
pub trait Leasing: AsRawFd + Seek + FileExt
{
	/// Acquires a whole of file lease.
	///
	/// An unprivileged process may take out a lease only on a file whose user identifier (owner) matches the filesystem user identifier (fsuid) of the process.
	/// A process with the `CAP_LEASE` capability may take out leases on arbitrary files.
	///
	/// Returns `true` if the lease was acquired or `false` if a signal interrupted whilst waiting to acquire a lease.
	#[inline(always)]
	fn acquire_lease(&self, lease: Lease) -> bool
	{
		let result = unsafe { fcntl(self.as_raw_fd(), F_SETLEASE, lease as i32) };

		if likely!(result == 0)
		{
			true
		}
		else if likely!(result == -1)
		{
			match errno().0
			{
				EINTR => false,
				EBADF => panic!("fd is not an open file descriptor"),
				EINVAL => panic!("operation is invalid"),

				unexpected @ _ => panic!("Unexpected error {} from fcntl()", unexpected)
			}
		}
		else
		{
			unreachable_code(format_args!("Unexpected result {} from fcntl()", result))
		}
	}

	/// Releases a file lease.
	///
	/// Returns `true` if the lease was released or `false` if a signal interrupted whilst waiting to release a lease.
	#[inline(always)]
	fn release_lease(&self) -> bool
	{
		let result = unsafe { fcntl(self.as_raw_fd(), F_SETLEASE, F_UNLCK) };

		if likely!(result == 0)
		{
			true
		}
		else if likely!(result == -1)
		{
			match errno().0
			{
				EINTR => false,
				EBADF => panic!("fd is not an open file descriptor"),
				EINVAL => panic!("operation is invalid"),

				unexpected @ _ => panic!("Unexpected error {} from fcntl()", unexpected)
			}
		}
		else
		{
			unreachable_code(format_args!("Unexpected result {} from fcntl()", result))
		}
	}

	/// Releases a file lease.
	///
	/// Returns `Some` if this open file description holds a lease or `None` if it doesn't.
	/// Returns an error if interupted by a signal.
	#[inline(always)]
	fn get_current_lease(&self) -> Result<Option<Lease>, ()>
	{
		use self::Lease::*;

		match unsafe { fcntl(self.as_raw_fd(), F_GETLEASE) }
		{
			F_RDLCK => Ok(Some(Read)),
			F_WRLCK => Ok(Some(Write)),
			F_UNLCK => Ok(None),

			-1 => match errno().0
			{
				EINTR => Err(()),
				EBADF => panic!("fd is not an open file descriptor"),
				EINVAL => panic!("operation is invalid"),

				unexpected @ _ => panic!("Unexpected error {} from fcntl()", unexpected)
			},

			result @ _ => panic!("Unexpected result {} from fcntl()", result)
		}
	}
}