mirror of https://github.com/octoleo/restic.git
54 lines
1.1 KiB
Go
54 lines
1.1 KiB
Go
//go:build !windows
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// +build !windows
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package restorer
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import "bytes"
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// WriteAt writes p to f.File at offset. It tries to do a sparse write
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// and updates f.size.
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func (f *partialFile) WriteAt(p []byte, offset int64) (n int, err error) {
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if !f.sparse {
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return f.File.WriteAt(p, offset)
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}
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n = len(p)
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// Skip the longest all-zero prefix of p.
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// If it's long enough, we can punch a hole in the file.
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skipped := zeroPrefixLen(p)
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p = p[skipped:]
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offset += int64(skipped)
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switch {
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case len(p) == 0:
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// All zeros, file already big enough. A previous WriteAt or
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// Truncate will have produced the zeros in f.File.
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default:
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var n2 int
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n2, err = f.File.WriteAt(p, offset)
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n = skipped + n2
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}
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return n, err
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}
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// zeroPrefixLen returns the length of the longest all-zero prefix of p.
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func zeroPrefixLen(p []byte) (n int) {
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// First skip 1kB-sized blocks, for speed.
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var zeros [1024]byte
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for len(p) >= len(zeros) && bytes.Equal(p[:len(zeros)], zeros[:]) {
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p = p[len(zeros):]
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n += len(zeros)
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}
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for len(p) > 0 && p[0] == 0 {
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p = p[1:]
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n++
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}
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return n
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}
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