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// Copyright 2020 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package lock provides POSIX and BSD style file locking for VFS2 file
// implementations.
//
// The actual implementations can be found in the lock package under
// sentry/fs/lock.
package vfs
import (
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/context"
fslock "gvisor.dev/gvisor/pkg/sentry/fs/lock"
"gvisor.dev/gvisor/pkg/syserror"
)
// FileLocks supports POSIX and BSD style locks, which correspond to fcntl(2)
// and flock(2) respectively in Linux. It can be embedded into various file
// implementations for VFS2 that support locking.
//
// Note that in Linux these two types of locks are _not_ cooperative, because
// race and deadlock conditions make merging them prohibitive. We do the same
// and keep them oblivious to each other.
type FileLocks struct {
// bsd is a set of BSD-style advisory file wide locks, see flock(2).
bsd fslock.Locks
// posix is a set of POSIX-style regional advisory locks, see fcntl(2).
posix fslock.Locks
}
// LockBSD tries to acquire a BSD-style lock on the entire file.
func (fl *FileLocks) LockBSD(uid fslock.UniqueID, t fslock.LockType, block fslock.Blocker) error {
if fl.bsd.LockRegion(uid, t, fslock.LockRange{0, fslock.LockEOF}, block) {
return nil
}
return syserror.ErrWouldBlock
}
// UnlockBSD releases a BSD-style lock on the entire file.
//
// This operation is always successful, even if there did not exist a lock on
// the requested region held by uid in the first place.
func (fl *FileLocks) UnlockBSD(uid fslock.UniqueID) {
fl.bsd.UnlockRegion(uid, fslock.LockRange{0, fslock.LockEOF})
}
// LockPOSIX tries to acquire a POSIX-style lock on a file region.
func (fl *FileLocks) LockPOSIX(ctx context.Context, fd *FileDescription, uid fslock.UniqueID, t fslock.LockType, start, length uint64, whence int16, block fslock.Blocker) error {
rng, err := computeRange(ctx, fd, start, length, whence)
if err != nil {
return err
}
if fl.posix.LockRegion(uid, t, rng, block) {
return nil
}
return syserror.ErrWouldBlock
}
// UnlockPOSIX releases a POSIX-style lock on a file region.
//
// This operation is always successful, even if there did not exist a lock on
// the requested region held by uid in the first place.
func (fl *FileLocks) UnlockPOSIX(ctx context.Context, fd *FileDescription, uid fslock.UniqueID, start, length uint64, whence int16) error {
rng, err := computeRange(ctx, fd, start, length, whence)
if err != nil {
return err
}
fl.posix.UnlockRegion(uid, rng)
return nil
}
func computeRange(ctx context.Context, fd *FileDescription, start uint64, length uint64, whence int16) (fslock.LockRange, error) {
var off int64
switch whence {
case linux.SEEK_SET:
off = 0
case linux.SEEK_CUR:
// Note that Linux does not hold any mutexes while retrieving the file
// offset, see fs/locks.c:flock_to_posix_lock and fs/locks.c:fcntl_setlk.
curOff, err := fd.Seek(ctx, 0, linux.SEEK_CUR)
if err != nil {
return fslock.LockRange{}, err
}
off = curOff
case linux.SEEK_END:
stat, err := fd.Stat(ctx, StatOptions{Mask: linux.STATX_SIZE})
if err != nil {
return fslock.LockRange{}, err
}
off = int64(stat.Size)
default:
return fslock.LockRange{}, syserror.EINVAL
}
return fslock.ComputeRange(int64(start), int64(length), off)
}
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