Future setup regression caused by 'mkdir: always check-for-existence' commit

[Achim Gratz]

Stephen Provine via cygwin writes:
> After this change (commit b0c033bf3fae810b9e5a5c69f17bd4de63725691),
> the Git for Windows setup (and future Cygwin setups) do not correctly
> configure bash features because the post-install step for configuring
> the /dev directory does not work any more.

Cygwin does not create these directories in postinstall nor does any
package provide them, setup.exe does.  So you can assume the existence
of these directories in Cygwin.

https://cygwin.com/cygwin-ug-net/using-specialnames.html

The /dev/std* links are created by bash postinstall and doing that still
works (and the link shows up in the backing filesystem, not just the
virtual one).

> It used to be that "mkdir -m 755 /dev" would succeed, but now it
> returns a "File exists" error, after which attempts to create the
> 'shm' and 'mqueue' directories fail and the /dev/fd,
> /dev/std{in,out,err} links are not created. This causes some bash
> features to not work. The fix (validated on Git for Windows) would be
> for setups to pre-create this directory outside of the Cygwin
> environment before running the post-install steps.

It seems mkdir gets spooked by the overlay of the virtual /dev over the
real one.  That's clearly a bug that needs fixing, IMHO.
You can work around by using a different path to the same directory (via
/proc/cygdrive, say).

> See
> https://github.com/git-for-windows/git/issues/2291#issuecomment-524433693
> for the in-depth analysis. Note, this is not a current issue in
> Cygwin, but is believed to become a FUTURE issue with the next
> release.

You can test that assumption by doing a fresh install of the current test version of Cygwin
3.1.0, but based on what I see on a system that has been updated to this
version I'd think Cygwin would not trigger this bug.


Regards,
Achim.
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