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// Copyright 2018 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package fs
import (
"math"
"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
)
// OffsetPageEnd returns the file offset rounded up to the nearest
// page boundary. OffsetPageEnd panics if rounding up causes overflow,
// which shouldn't be possible given that offset is an int64.
func OffsetPageEnd(offset int64) uint64 {
end, ok := usermem.Addr(offset).RoundUp()
if !ok {
panic("impossible overflow")
}
return uint64(end)
}
// ReadEndOffset returns an exclusive end offset for a read operation
// so that the read does not overflow an int64 nor size.
//
// Parameters:
// - offset: the starting offset of the read.
// - length: the number of bytes to read.
// - size: the size of the file.
//
// Postconditions: The returned offset is >= offset.
func ReadEndOffset(offset int64, length int64, size int64) int64 {
if offset >= size {
return offset
}
end := offset + length
// Don't overflow.
if end < offset || end > size {
end = size
}
return end
}
// WriteEndOffset returns an exclusive end offset for a write operation
// so that the write does not overflow an int64.
//
// Parameters:
// - offset: the starting offset of the write.
// - length: the number of bytes to write.
//
// Postconditions: The returned offset is >= offset.
func WriteEndOffset(offset int64, length int64) int64 {
return ReadEndOffset(offset, length, math.MaxInt64)
}
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