Why does Cygwin always use absolute paths instead of OBJECT_ATTRIBUTES.RootDirectory?

[Jakob Bohm]

On 04/02/2026 23:50, Dan Shelton via Cygwin wrote:
> On Wed, 4 Feb 2026 at 22:37, Brian Inglis via Cygwin <cygwin@cygwin.com> wrote:
>> On 2026-02-04 14:17, Dan Shelton via Cygwin wrote:
>>> Why does Cygwin always use absolute paths instead of
>>> OBJECT_ATTRIBUTES.RootDirectory in NtOpenFile(),
>>> NtSetInformationFile() for rename and hardlinks
>>>
>>> This slows down Cygwin path lookups a lot, and with lots of path
>>> elements each lookup with a relative RootDirectory might be a lot
>>> faster, e.g. for openat(), linkat(), renameat().
>> Because volunteers' spare time is limited, and performance is good enough for
>> those who might do the work:
> Please do not slap me. That hurt.
>
> My question is about whether there are any technical issues which
> prevent OBJECT_ATTRIBUTES.RootDirectory from being used in Cygwin for
> openat().
>
> 2nd question: Is OBJECT_ATTRIBUTES.RootDirectory really a root, and
> you cannot do cd ..?
>
Take a look at the openat(3P) function, it seems to be what you are 
looking for.

Enjoy

Jakob
-- 
Jakob Bohm, CIO, Partner, WiseMo A/S.  https://www.wisemo.com
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