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