github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/vdso/seqlock.h (about)

     1  // Copyright 2018 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  // Low level raw interfaces to the sequence counter used by the VDSO.
    16  #ifndef VDSO_SEQLOCK_H_
    17  #define VDSO_SEQLOCK_H_
    18  
    19  #include <stdint.h>
    20  
    21  #include "vdso/barrier.h"
    22  #include "vdso/compiler.h"
    23  
    24  namespace vdso {
    25  
    26  inline int32_t read_seqcount_begin(const uint64_t* s) {
    27    uint64_t seq = *s;
    28    read_barrier();
    29    return seq & ~1;
    30  }
    31  
    32  inline int read_seqcount_retry(const uint64_t* s, uint64_t seq) {
    33    read_barrier();
    34    return unlikely(*s != seq);
    35  }
    36  
    37  }  // namespace vdso
    38  
    39  #endif  // VDSO_SEQLOCK_H_