sdk/fidl/fuchsia.io2/locking.fidl

// Copyright 2020 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

library fuchsia.io2;

using zx;

/// Advisory locking protocol.
///
/// This protocol is intended to be composed into the |File| protocol to
/// provide support for advisory locking.
///
/// Advisory locks are purely advisory. They do not prevent actual read or
/// write operations from occurring on the file, either through this
/// connection or through other connections.
///
/// These primitives are designed to support the flock() and fcntl(),
/// specifically F_SETLK, F_SETLKW, and F_GETLK, functionality that code
/// running on Fuchsia expects from other operating systems.
protocol AdvisoryLocking {
    /// Acquires an advisory lock on the underlying file.
    ///
    /// The lock lasts until either this connection is closed or
    /// this method is called with |AdvisoryLockType.UNLOCK| to release the lock
    /// explicitly.
    ///
    /// Advisory locks are purely advisory. They do not prevent actual read or
    /// write operations from occurring on the file, either through this
    /// connection or through other connections.
    ///
    /// This method requires the following rights:
    ///
    /// * [`Rights.READ_BYTES`] if `request.type` is [`AdvisoryLockType.READ`].
    /// * [`Rights.WRITE_BYTES`] if `request.type` is
    ///   [`AdvisoryLockType.WRITE`].
    ///
    /// # Errors
    ///
    /// * `ZX_ERR_BAD_STATE` The specified type of lock cannot be acquired. For
    ///   example, another connection might hold a conflicting lock type.
    /// * `ZX_ERR_NOT_SUPPORTED` This file does not support advisory locking.
    /// * `ZX_ERR_ACCESS_DENIED` This connection does not have sufficient rights
    ///   to acquire the given type of lock.
    [Transitional]
    AdvisoryLock(AdvisoryLockRequest request) -> () error zx.status;
};

/// A type of advisory lock.
///
/// Used with [`AdvisoryLocking.AdvisoryLock`].
enum AdvisoryLockType : uint32 {
    /// Zero or more connections can hold read locks on a file simultaneously.
    READ = 1;

    /// At most one connection can hold a write lock on a file simultaneously.
    /// When a write lock is held on a file, no other types of locks can be held
    /// on that file.
    WRITE = 2;

    /// The region specifies a region to be unlocked.
    UNLOCK = 3;
};

/// A range within a file associated with an advisory lock.
///
/// The range can extend beyond the end of the file but cannot extend beyond
/// the beginning of the file.
struct AdvisoryLockRange {
    /// The location in the file from which [`offset`] is computed.
    SeekOrigin origin;

    /// The start of the byte range, expressed as an offset from [`origin`].
    /// Cannot be negative if [`origin`] is [`SeekOrigin.START`].
    int64 offset;

    /// The length of the byte range in bytes.
    ///
    /// If the length is zero, then the byte range exends until the end of the
    /// file, regardless of how large the file becomes.
    ///
    /// If the length is negative, the byte range includes the bytes `offset` +
    /// `length` up to, and including, `offset` - 1, provided this range does
    /// not extend beyond the beginning of the file.
    int64 length;
};

table AdvisoryLockRequest {
    /// The type of lock to be acquired.
    ///
    /// If this field is absent, the [`AdvisoryLock`] method will fail
    /// with ZX_ERR_INVALID_ARGS.
    1: AdvisoryLockType type;

    /// The byte range within the file to be locked. See [`AdvisoryLockRange`]
    /// for semantics.
    ///
    /// If this field is absent, the range defaults to the entire file.
    2: AdvisoryLockRange range;

    /// Whether the file should wait reply to the [`AdvisoryLock`]
    /// method until the requested lock can be acquired.
    ///
    /// If this field is absent, the file will not wait.
    3: bool wait;
};