os: SMB not respecting calls to os.Chtimes (from windows)

[spf13]

Mentioned in #31880

What version of Go are you using (go version)?

$ go version go1.12.7 windows/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
amd64

windows

What did you do?

I wrote a program that copies media files from one location to another and sets the ctime and mtime to the original file timestamp. The program copies a file and changes the date using io.Copy(destFile, srcFile) then calls os.Chtimes(dest, t.AccessTime(), t.ModTime()) to set the dates.

What did you expect to see?

The dates to change to the dates provided... or an error at least. This silently fails.

What did you see instead?

It works appropriately in most cases, but when copying from a windows machine to a Linux SMB server the destination date is always set to now instead of changing to the src date.

It works from Windows to Windows and from Mac to Mac. I haven't tried other combinations yet.

[julieqiu]

/cc @bradfitz @ianlancetaylor

[alexbrainman]

I could reproduce this problem, but only in very special circumstances.

I could not reproduce the problem, if I do file time stamp reading from Windows. I used both os.File.Stat and shelling out with cmd.exe /c dir ... for every test program I tried, and time stamps are as expected. I could only reproduce this problem, if I create file from Windows Go program, and then use stat or ls -l command on Linux to view created file times.

I managed reproduce the problem with this program https://play.golang.org/p/OVLuYilFE7E

But, if I add f.Close() after line 39, the problem goes away.

I can also make problem go away, if I add

        err = f.Sync()
        if err != nil {
                t.Fatal(err)
        }

after line 39.

I don't know @spf13 what your problem is (you did not provide your program), but I suspect that Samba updates modtime when file is written to, but writes might be buffered on the client side. On the other hand, Samba Windows SetFileTime API implementation (Go uses SetFileTime to implement os.Chtimes) is not buffered.

I am not sure if there is anything more we could do here.

Alex

[zhucan]

@spf13 Is there some way to solve it?