github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/pkg/sentry/vfs/lock.go (about)

     1  // Copyright 2020 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package vfs
    16  
    17  import (
    18  	"github.com/SagerNet/gvisor/pkg/abi/linux"
    19  	"github.com/SagerNet/gvisor/pkg/context"
    20  	fslock "github.com/SagerNet/gvisor/pkg/sentry/fs/lock"
    21  	"github.com/SagerNet/gvisor/pkg/syserror"
    22  )
    23  
    24  // FileLocks supports POSIX and BSD style locks, which correspond to fcntl(2)
    25  // and flock(2) respectively in Linux. It can be embedded into various file
    26  // implementations for VFS2 that support locking.
    27  //
    28  // Note that in Linux these two types of locks are _not_ cooperative, because
    29  // race and deadlock conditions make merging them prohibitive. We do the same
    30  // and keep them oblivious to each other.
    31  //
    32  // +stateify savable
    33  type FileLocks struct {
    34  	// bsd is a set of BSD-style advisory file wide locks, see flock(2).
    35  	bsd fslock.Locks
    36  
    37  	// posix is a set of POSIX-style regional advisory locks, see fcntl(2).
    38  	posix fslock.Locks
    39  }
    40  
    41  // LockBSD tries to acquire a BSD-style lock on the entire file.
    42  func (fl *FileLocks) LockBSD(ctx context.Context, uid fslock.UniqueID, ownerID int32, t fslock.LockType, block fslock.Blocker) error {
    43  	if fl.bsd.LockRegion(uid, ownerID, t, fslock.LockRange{0, fslock.LockEOF}, block) {
    44  		return nil
    45  	}
    46  
    47  	// Return an appropriate error for the unsuccessful lock attempt, depending on
    48  	// whether this is a blocking or non-blocking operation.
    49  	if block == nil {
    50  		return syserror.ErrWouldBlock
    51  	}
    52  	return syserror.ERESTARTSYS
    53  }
    54  
    55  // UnlockBSD releases a BSD-style lock on the entire file.
    56  //
    57  // This operation is always successful, even if there did not exist a lock on
    58  // the requested region held by uid in the first place.
    59  func (fl *FileLocks) UnlockBSD(uid fslock.UniqueID) {
    60  	fl.bsd.UnlockRegion(uid, fslock.LockRange{0, fslock.LockEOF})
    61  }
    62  
    63  // LockPOSIX tries to acquire a POSIX-style lock on a file region.
    64  func (fl *FileLocks) LockPOSIX(ctx context.Context, uid fslock.UniqueID, ownerPID int32, t fslock.LockType, r fslock.LockRange, block fslock.Blocker) error {
    65  	if fl.posix.LockRegion(uid, ownerPID, t, r, block) {
    66  		return nil
    67  	}
    68  
    69  	// Return an appropriate error for the unsuccessful lock attempt, depending on
    70  	// whether this is a blocking or non-blocking operation.
    71  	if block == nil {
    72  		return syserror.ErrWouldBlock
    73  	}
    74  	return syserror.ERESTARTSYS
    75  }
    76  
    77  // UnlockPOSIX releases a POSIX-style lock on a file region.
    78  //
    79  // This operation is always successful, even if there did not exist a lock on
    80  // the requested region held by uid in the first place.
    81  func (fl *FileLocks) UnlockPOSIX(ctx context.Context, uid fslock.UniqueID, r fslock.LockRange) error {
    82  	fl.posix.UnlockRegion(uid, r)
    83  	return nil
    84  }
    85  
    86  // TestPOSIX returns information about whether the specified lock can be held, in the style of the F_GETLK fcntl.
    87  func (fl *FileLocks) TestPOSIX(ctx context.Context, uid fslock.UniqueID, t fslock.LockType, r fslock.LockRange) (linux.Flock, error) {
    88  	return fl.posix.TestRegion(ctx, uid, t, r), nil
    89  }