github.com/MerlinKodo/gvisor@v0.0.0-20231110090155-957f62ecf90e/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/MerlinKodo/gvisor/pkg/abi/linux"
    19  	"github.com/MerlinKodo/gvisor/pkg/context"
    20  	"github.com/MerlinKodo/gvisor/pkg/errors/linuxerr"
    21  	fslock "github.com/MerlinKodo/gvisor/pkg/sentry/fsimpl/lock"
    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 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 bool) error {
    43  	if err := fl.bsd.LockRegion(ctx, uid, ownerID, t, fslock.LockRange{0, fslock.LockEOF}, false, block); err == nil || err == linuxerr.ErrWouldBlock {
    44  		return err
    45  	}
    46  	return linuxerr.ERESTARTSYS
    47  }
    48  
    49  // UnlockBSD releases a BSD-style lock on the entire file.
    50  //
    51  // This operation is always successful, even if there did not exist a lock on
    52  // the requested region held by uid in the first place.
    53  func (fl *FileLocks) UnlockBSD(uid fslock.UniqueID) {
    54  	fl.bsd.UnlockRegion(uid, fslock.LockRange{0, fslock.LockEOF})
    55  }
    56  
    57  // LockPOSIX tries to acquire a POSIX-style lock on a file region.
    58  func (fl *FileLocks) LockPOSIX(ctx context.Context, uid fslock.UniqueID, ownerPID int32, t fslock.LockType, r fslock.LockRange, block bool) error {
    59  	_, ofd := uid.(*FileDescription)
    60  	if err := fl.posix.LockRegion(ctx, uid, ownerPID, t, r, ofd, block); err == nil || err == linuxerr.ErrWouldBlock {
    61  		return err
    62  	}
    63  	return linuxerr.ERESTARTSYS
    64  }
    65  
    66  // UnlockPOSIX releases a POSIX-style lock on a file region.
    67  //
    68  // This operation is always successful, even if there did not exist a lock on
    69  // the requested region held by uid in the first place.
    70  func (fl *FileLocks) UnlockPOSIX(ctx context.Context, uid fslock.UniqueID, r fslock.LockRange) error {
    71  	fl.posix.UnlockRegion(uid, r)
    72  	return nil
    73  }
    74  
    75  // TestPOSIX returns information about whether the specified lock can be held, in the style of the F_GETLK fcntl.
    76  func (fl *FileLocks) TestPOSIX(ctx context.Context, uid fslock.UniqueID, t fslock.LockType, r fslock.LockRange) (linux.Flock, error) {
    77  	_, ofd := uid.(*FileDescription)
    78  	return fl.posix.TestRegion(ctx, uid, t, r, ofd), nil
    79  }