72 lines
2.1 KiB
Go
72 lines
2.1 KiB
Go
package main
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import (
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"fmt"
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"os"
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)
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// PathInfo describes a source/dest path as seen locally by whichever
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// process (control agent, sink, source-stream) actually opens it.
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type PathInfo struct {
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Exists bool
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IsDevice bool
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Size int64
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}
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// alignmentFor returns the offset/length alignment a path's handle requires
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// for positioned reads and writes. Linux block devices accept ordinary
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// buffered pread/pwrite at any alignment, so there is nothing to round to.
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func alignmentFor(string) int64 { return 1 }
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// canElevate reports whether a permission failure opening a device is worth
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// retrying under `sudo` (see --sudo).
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func canElevate() bool { return true }
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func statPath(path string) (PathInfo, error) {
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fi, err := os.Stat(path)
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if err != nil {
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if os.IsNotExist(err) {
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return PathInfo{Exists: false}, nil
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}
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return PathInfo{}, err
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}
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mode := fi.Mode()
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isDevice := mode&os.ModeDevice != 0 && mode&os.ModeCharDevice == 0
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size := fi.Size()
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if isDevice {
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sz, err := blockDeviceSize(path)
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if err != nil {
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return PathInfo{}, fmt.Errorf("stat block device %s: %w", path, err)
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}
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size = sz
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}
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return PathInfo{Exists: true, IsDevice: isDevice, Size: size}, nil
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}
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// prepareDest makes the destination ready to receive exactly targetSize
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// bytes: a regular file is created if missing and truncated (grown or
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// shrunk) to targetSize; a block device is only validated to be large
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// enough (it can't be resized) — the caller is expected to have already
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// capped targetSize at the device's own size when it is the limiting side.
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func prepareDest(path string, targetSize int64) error {
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info, err := statPath(path)
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if err != nil {
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return err
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}
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if info.Exists && info.IsDevice {
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if targetSize > info.Size {
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return fmt.Errorf("destination device %s is only %d bytes, need %d", path, info.Size, targetSize)
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}
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return nil
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}
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f, err := os.OpenFile(path, os.O_CREATE|os.O_WRONLY, 0644)
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if err != nil {
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return fmt.Errorf("open/create %s: %w", path, err)
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}
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defer f.Close()
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if err := f.Truncate(targetSize); err != nil {
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return fmt.Errorf("truncate %s to %d: %w", path, targetSize, err)
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}
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return nil
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}
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