73 lines
2.6 KiB
Go
73 lines
2.6 KiB
Go
// Copyright 2020 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package lock provides POSIX and BSD style file locking for VFS2 file
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// implementations.
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//
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// The actual implementations can be found in the lock package under
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// sentry/fs/lock.
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package lock
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import (
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fslock "gvisor.dev/gvisor/pkg/sentry/fs/lock"
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"gvisor.dev/gvisor/pkg/syserror"
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)
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// FileLocks supports POSIX and BSD style locks, which correspond to fcntl(2)
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// and flock(2) respectively in Linux. It can be embedded into various file
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// implementations for VFS2 that support locking.
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//
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// Note that in Linux these two types of locks are _not_ cooperative, because
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// race and deadlock conditions make merging them prohibitive. We do the same
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// and keep them oblivious to each other.
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type FileLocks struct {
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// bsd is a set of BSD-style advisory file wide locks, see flock(2).
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bsd fslock.Locks
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// posix is a set of POSIX-style regional advisory locks, see fcntl(2).
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posix fslock.Locks
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}
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// LockBSD tries to acquire a BSD-style lock on the entire file.
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func (fl *FileLocks) LockBSD(uid fslock.UniqueID, t fslock.LockType, block fslock.Blocker) error {
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if fl.bsd.LockRegion(uid, t, fslock.LockRange{0, fslock.LockEOF}, block) {
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return nil
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}
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return syserror.ErrWouldBlock
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}
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// UnlockBSD releases a BSD-style lock on the entire file.
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//
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// This operation is always successful, even if there did not exist a lock on
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// the requested region held by uid in the first place.
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func (fl *FileLocks) UnlockBSD(uid fslock.UniqueID) {
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fl.bsd.UnlockRegion(uid, fslock.LockRange{0, fslock.LockEOF})
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}
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// LockPOSIX tries to acquire a POSIX-style lock on a file region.
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func (fl *FileLocks) LockPOSIX(uid fslock.UniqueID, t fslock.LockType, rng fslock.LockRange, block fslock.Blocker) error {
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if fl.posix.LockRegion(uid, t, rng, block) {
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return nil
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}
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return syserror.ErrWouldBlock
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}
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// UnlockPOSIX releases a POSIX-style lock on a file region.
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//
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// This operation is always successful, even if there did not exist a lock on
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// the requested region held by uid in the first place.
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func (fl *FileLocks) UnlockPOSIX(uid fslock.UniqueID, rng fslock.LockRange) {
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fl.posix.UnlockRegion(uid, rng)
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}
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