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save: Use dd with the notrunc & fsync and postpone truncation #3814

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Merged
JoeKar merged 2 commits into from
Aug 12, 2025
Merged

save: Use dd with the notrunc & fsync and postpone truncation #3814

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87ce573
save: gofmt
JoeKar Jul 23, 2025
165a5a4
save: Use `dd` with the `notrunc` & `fsync` option
JoeKar Jul 22, 2025
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32 changes: 23 additions & 9 deletions internal/buffer/save.go
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@ import (
const LargeFileThreshold = 50000

type wrappedFile struct {
name string
writeCloser io.WriteCloser
withSudo bool
screenb bool
Expand Down Expand Up @@ -83,7 +84,13 @@ func openFile(name string, withSudo bool) (wrappedFile, error) {
var sigChan chan os.Signal

if withSudo {
cmd = exec.Command(config.GlobalSettings["sucmd"].(string), "dd", "bs=4k", "of="+name)
conv := "notrunc"
// TODO: both platforms do not support dd with conv=fsync yet
if !(runtime.GOOS == "illumos" || runtime.GOOS == "netbsd") {
conv += ",fsync"
}

cmd = exec.Command(config.GlobalSettings["sucmd"].(string), "dd", "bs=4k", "conv="+conv, "of="+name)
writeCloser, err = cmd.StdinPipe()
if err != nil {
return wrappedFile{}, err
Expand Down Expand Up @@ -113,7 +120,18 @@ func openFile(name string, withSudo bool) (wrappedFile, error) {
}
}

return wrappedFile{writeCloser, withSudo, screenb, cmd, sigChan}, nil
return wrappedFile{name, writeCloser, withSudo, screenb, cmd, sigChan}, nil
}

func (wf wrappedFile) Truncate() error {
if wf.withSudo {
// we don't need to stop the screen here, since it is still stopped
// by openFile()
// truncate might not be available on every platfom, so use dd instead
cmd := exec.Command(config.GlobalSettings["sucmd"].(string), "dd", "count=0", "of="+wf.name)
return cmd.Run()
}
return wf.writeCloser.(*os.File).Truncate(0)
}

func (wf wrappedFile) Write(b *Buffer) (int, error) {
Expand All @@ -134,12 +152,9 @@ func (wf wrappedFile) Write(b *Buffer) (int, error) {
eol = []byte{'\n'}
}

if !wf.withSudo {
f := wf.writeCloser.(*os.File)
err := f.Truncate(0)
if err != nil {
return 0, err
}
err := wf.Truncate()
if err != nil {
return 0, err
}

// write lines
Expand Down Expand Up @@ -374,7 +389,6 @@ func (b *Buffer) safeWrite(path string, withSudo bool, newFile bool) (int, error
}
}()


// Try to backup first before writing
backupName, err := b.writeBackup(path)
if err != nil {
Expand Down
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