github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/pkg/sentry/fs/offset.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  	"math"
    19  
    20  	"github.com/SagerNet/gvisor/pkg/hostarch"
    21  )
    22  
    23  // OffsetPageEnd returns the file offset rounded up to the nearest
    24  // page boundary. OffsetPageEnd panics if rounding up causes overflow,
    25  // which shouldn't be possible given that offset is an int64.
    26  func OffsetPageEnd(offset int64) uint64 {
    27  	end, ok := hostarch.Addr(offset).RoundUp()
    28  	if !ok {
    29  		panic("impossible overflow")
    30  	}
    31  	return uint64(end)
    32  }
    33  
    34  // ReadEndOffset returns an exclusive end offset for a read operation
    35  // so that the read does not overflow an int64 nor size.
    36  //
    37  // Parameters:
    38  // - offset: the starting offset of the read.
    39  // - length: the number of bytes to read.
    40  // - size:   the size of the file.
    41  //
    42  // Postconditions: The returned offset is >= offset.
    43  func ReadEndOffset(offset int64, length int64, size int64) int64 {
    44  	if offset >= size {
    45  		return offset
    46  	}
    47  	end := offset + length
    48  	// Don't overflow.
    49  	if end < offset || end > size {
    50  		end = size
    51  	}
    52  	return end
    53  }
    54  
    55  // WriteEndOffset returns an exclusive end offset for a write operation
    56  // so that the write does not overflow an int64.
    57  //
    58  // Parameters:
    59  // - offset: the starting offset of the write.
    60  // - length: the number of bytes to write.
    61  //
    62  // Postconditions: The returned offset is >= offset.
    63  func WriteEndOffset(offset int64, length int64) int64 {
    64  	return ReadEndOffset(offset, length, math.MaxInt64)
    65  }