Re: [hackers] [sbase] [PATCH] mkfifo: Simplify -m handling

From: Richard Ipsum <richardipsum_AT_fastmail.co.uk>
Date: Fri, 14 Jun 2019 09:57:10 +0100

On Thu, Jun 13, 2019 at 05:27:37PM -0700, Michael Forney wrote:
> Thanks for looking this over.
>
> On 2019-06-13, Richard Ipsum <richardipsum_AT_fastmail.co.uk> wrote:
> > I might be wrong but I think this will cause a subtle change in
> > behaviour since the umask is needed to correctly interpret the mode
> > string. One example that's documented in chmod(1p) is "-w" vs "a-w".
> > "a-w" removes all write perms, but "-w" removes only the permissions
> > that weren't filtered by the mask. This could explain why this
> > is currently being done in two separate steps.
>
> umask(0) sets the mask to 0 and returns the old mask, so I think the
> mode is interpreted the same way before and after this change
> (getumask() is even implemented as two calls to umask, returning the
> result of the first call).

Ah right, I read this thinking the mask passed to the mode string
parser would be 0, but obviously it's not. So you pass the existing
mode while setting the mask to 0 so that you can use the final mode
as the argument to mkfifo, and get rid of the chmod call, nice.

Thanks,
Richard
Received on Fri Jun 14 2019 - 10:57:10 CEST