os: MkdirAll fails on Windows with extended volume name syntax

[ncw]

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

go version devel +18bcc7c285 Tue Jun 23 14:32:35 2020 +0000 linux/amd64

Does this issue reproduce with the latest release?

Yes, the above is latest tip

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

Tested with Windows 10 with a binary cross compiled from Linux.

Here is go env from the Windows box (which isn't running go-tip as I don't know how to compile it on Windows!)

go env Output

set GO111MODULE=
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\Dev\AppData\Local\go-build
set GOENV=C:\Users\Dev\AppData\Roaming\go\env
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\Dev\go
set GOPRIVATE=
set GOPROXY=https://proxy.golang.org,direct
set GOROOT=c:\go
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLDIR=c:\go\pkg\tool\windows_amd64
set GCCGO=gccgo
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=C:\Users\Dev\AppData\Local\Temp\go-build801995766=/tmp/go-build -gno-record-gcc-switches

What did you do?

I ran this program

package main

import (
	"fmt"
	"os"
)

func main() {
	for _, arg := range os.Args[1:] {
		fmt.Printf("About to MkdirAll(%q)\n", arg)
		err := os.MkdirAll(arg, 0777)
		if err != nil {
			fmt.Printf("...Returned error: %v\n", err)
		} else {
			fmt.Printf("...OK\n")
		}
	}
}

With the extended volume name from mountvol.exe (run mountvol to see the extended name for your disk)

I ran

mkdirall.exe \\?\Volume{97bb9c9b-0000-0000-0000-402400000000}\go-test

What did you expect to see?

I expected this to create the go-test directory on C:

What did you see instead?

Z:\>mkdirall.exe \\?\Volume{97bb9c9b-0000-0000-0000-402400000000}\go-test
About to MkdirAll("\\\\?\\Volume{97bb9c9b-0000-0000-0000-402400000000}\\go-test")
...Returned error: mkdir \\?: The filename, directory name, or volume label syntax is incorrect.

Note that this succeeds if the directory already exists

Z:\>mkdir \\?\Volume{97bb9c9b-0000-0000-0000-402400000000}\mkdir-test

Z:\>dir \\?\Volume{97bb9c9b-0000-0000-0000-402400000000}\mkdir-test
 Volume in drive \\?\Volume{97bb9c9b-0000-0000-0000-402400000000} has no label.
 Volume Serial Number is 464C-ABA7

 Directory of \\?\Volume{97bb9c9b-0000-0000-0000-402400000000}\mkdir-test

23/06/2020  17:41    <DIR>          .
23/06/2020  17:41    <DIR>          ..
               0 File(s)              0 bytes
               2 Dir(s)   9,107,767,296 bytes free

Z:\>mkdirall.exe \\?\Volume{97bb9c9b-0000-0000-0000-402400000000}\mkdir-test
About to MkdirAll("\\\\?\\Volume{97bb9c9b-0000-0000-0000-402400000000}\\mkdir-test")
...OK

This may be related to #22230

[cagedmantis]

At first glance, it certainly seems related to #22230

[cagedmantis]

/cc @rsc @robpike @ianlancetaylor @bradfitz @griesemer

[ianlancetaylor]

CC @alexbrainman

[networkimprov]

Related: #39786

cc @bcmills

[ericwj]

Consider weighing in on #40104 to see issues like this finally be resolved once and forever.

[gopherbot]

Change https://go.dev/cl/517015 mentions this issue: os: make MkdirAll support volume names