github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/pkg/sentry/fs/dirent_cache_limiter.go (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  package fs
    16  
    17  import (
    18  	"fmt"
    19  
    20  	"github.com/SagerNet/gvisor/pkg/sync"
    21  )
    22  
    23  // DirentCacheLimiter acts as a global limit for all dirent caches in the
    24  // process.
    25  //
    26  // +stateify savable
    27  type DirentCacheLimiter struct {
    28  	mu    sync.Mutex `state:"nosave"`
    29  	max   uint64
    30  	count uint64 `state:"zerovalue"`
    31  }
    32  
    33  // NewDirentCacheLimiter creates a new DirentCacheLimiter.
    34  func NewDirentCacheLimiter(max uint64) *DirentCacheLimiter {
    35  	return &DirentCacheLimiter{max: max}
    36  }
    37  
    38  func (d *DirentCacheLimiter) tryInc() bool {
    39  	d.mu.Lock()
    40  	if d.count >= d.max {
    41  		d.mu.Unlock()
    42  		return false
    43  	}
    44  	d.count++
    45  	d.mu.Unlock()
    46  	return true
    47  }
    48  
    49  func (d *DirentCacheLimiter) dec() {
    50  	d.mu.Lock()
    51  	if d.count == 0 {
    52  		panic(fmt.Sprintf("underflowing DirentCacheLimiter count: %+v", d))
    53  	}
    54  	d.count--
    55  	d.mu.Unlock()
    56  }