Before the change:

% go test -v -run  '^TestMkdirAll$'
=== RUN   TestMkdirAll
/tmp is a directory
Mkdir /tmp/_TestMkdirAll_
Mkdir /tmp/_TestMkdirAll_/dir
Mkdir /tmp/_TestMkdirAll_/dir/.
Mkdir /tmp/_TestMkdirAll_/dir/./dir2
/tmp/_TestMkdirAll_/dir/./dir2 is a directory
/tmp/_TestMkdirAll_/dir/./dir2/file is a file
/tmp/_TestMkdirAll_/dir/./dir2/file is a file
--- PASS: TestMkdirAll (0.01s)
PASS
ok  	os	0.052s

After the change:

% go test -v -run  '^TestMkdirAll$'
=== RUN   TestMkdirAll
/tmp/ is a directory
Mkdir /tmp/_TestMkdirAll_/
Mkdir /tmp/_TestMkdirAll_/dir/
Mkdir /tmp/_TestMkdirAll_/dir/./
Mkdir /tmp/_TestMkdirAll_/dir/./dir2
/tmp/_TestMkdirAll_/dir/./dir2 is a directory
/tmp/_TestMkdirAll_/dir/./dir2/file is a file
/tmp/_TestMkdirAll_/dir/./dir2/ is a directory
Mkdir /tmp/_TestMkdirAll_/dir/./dir2/file/
Mkdir /tmp/_TestMkdirAll_/dir/./dir2/file/subdir
--- FAIL: TestMkdirAll (0.02s)
	path_test.go:67: MkdirAll "/tmp/_TestMkdirAll_/dir/./dir2/file/subdir" returned wrong error path: "/tmp/_TestMkdirAll_/dir/dir2/file/subdir" not "/tmp/_TestMkdirAll_/dir/dir2/file"
FAIL
exit status: 'os.test 374140: 1'
FAIL	os	0.057s

This issues emphases a specific behavior on Plan 9. It can be reproduced this way:

% mkdir -p /tmp/_TestMkdirAll_/dir/./dir2
% > /tmp/_TestMkdirAll_/dir/./dir2/file
% mkdir /tmp/_TestMkdirAll_/dir/./dir2/file/
% mkdir /tmp/_TestMkdirAll_/dir/./dir2/file
mkdir: /tmp/_TestMkdirAll_/dir/./dir2/file already exists

Mkdir("file") will return an error, while Mkdir("file/") won't.

@0intro I filled #23902 yesterday about this. I have no idea how to fix this on plan9. Do you want me to revert CL 86295 ? Or should we adjust CL 86295 to do nothing on plan9?

Alex

Sorry, it seems I've missed your issue.

I'm not sure how to fix this issue properly on Plan 9 yet. Should we change the behavior of the fstat syscall in the Plan 9 kernel? Should we remove trailing slashes in the implementation of os.Stat or dirstat on Plan 9?

I think the safest change for now would be to add an exception for Plan 9 in the implementation of os.MkdirAll, so we get the same behavior as before. I'll propose a CL.

Sorry, it seems I've missed your issue.

No worries. Sorry for breaking plan9 build.

I think the safest change for now would be to add an exception for Plan 9 in the implementation of os.MkdirAll, so we get the same behavior as before.

I was going to suggest the same,

I'll propose a CL.

Thank you. Feel free to put me as a reviewer. I will push +2 button if I am not in bed.

Alex

MkdirAll is now being called with a trailing slash on the path. In the case where the path exists and is a file, the "fast path" code will now be bypassed -- on all platforms, not just Plan 9 -- because the Stat in line 22 returns error "not a directory", and therefore the dir.IsDir call will never be executed.

The Plan 9 misbehaviour is actually independent of the trailing slash -- the underlying system call

create(path, OREAD, DMDIR | mode)

doesn't return an error if path exists and is a file, whether or not it ends in a slash.

In the altered MkdirAll, it might be a good idea to check the error from the first Stat with IsNotexist, to reinstate the fast path in the case of a file.

But I think we should workaround the underlying Plan 9 problem by having syscall.Mkdir check for pre-existing path, and not relying on the system call to do it right.

Change https://golang.org/cl/95055 mentions this issue: os: fix MkdirAll on Plan 9

@millerresearch Yes, you're right. Could you submit a CL?

We could also just revert CL 86295 and I will try to find different fix for CL CL 86295.
What do you think?

Alex

@0intro, I think the change should be runtime.GOOS != "windows" instead of runtime.GOOS == "plan9", because the stat behaviour is common to other platforms: when the the path ends with a slash but the named file is not a directory, stat returns a "not a directory" error instead of just reporting the file exists.

Independent of this correction, I think I have a workaround for the silly Plan 9 behaviour of syscall.Mkdir, so I'll submit a CL for that.

Change https://golang.org/cl/94777 mentions this issue: syscall: ensure Mkdir(path) on Plan 9 fails if path exists

Change https://golang.org/cl/95095 mentions this issue: os: fix fast path in MkdirAll

I've replaced CL 95055 by CL 95095 with a more general subject and description.

Change https://golang.org/cl/95255 mentions this issue: path: use OS-specific function in MkdirAll, don't always keep trailing slash