On Feb 4 23:50, Dan Shelton via Cygwin wrote: > On Wed, 4 Feb 2026 at 22:37, Brian Inglis via Cygwin <[email protected]> > 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().
Yes. Obviously it would be nice to be able to use relative paths and a dir handle with openat and friends, but there are a few technical reasons not to do that: - Relative paths are length restricted. They can only contain up to 256 chars. - Relative paths can't contain ".." and ".", so you can't do something like openat (dirfd, "../myfile", ...) without changing the path to an absolute path. - Relative paths could cross Cygwin symlinks and Cygwin mount points. - Relative paths could just as well cross virtual FS boundaries, like /proc, /dev/. - Last but not least, the underlying path_conv class doesn't handle directory handle relative paths. The history of this function is just as old as Cygwin itself, about 30 years. I took a stab at rewriting the function a couple of times in the last couple of years but never got around to any workable code before giving up. It's a pretty convoluted piece of code and writing a drop-in replacement is a multi-month job. This very much collides with my day job, which isn't Cygwin-related at all. > 2nd question: Is OBJECT_ATTRIBUTES.RootDirectory really a root, and > you cannot do cd ..? If I understand your question correctly, yes. Because of the second bullet point above. Corinna -- Problem reports: https://cygwin.com/problems.html FAQ: https://cygwin.com/faq/ Documentation: https://cygwin.com/docs.html Unsubscribe info: https://cygwin.com/ml/#unsubscribe-simple
