Cygwin pathconf() query filesystem kernel data? Re: How does Cygwin detect MSFT NFSv3 file system? Re: Weird (path) problems with cygwin test release 3.5.0-0.384.g9939aa7d0945.x86_64 ...

[Martin Wege]

On Tue, Aug 22, 2023 at 12:07 AM Brian Inglis <Brian.Inglis@shaw.ca> wrote:
>
> On 2023-08-21 06:03, Martin Wege via Cygwin wrote:
> > On Sat, Aug 19, 2023 at 7:50 PM Brian Inglis <Brian.Inglis@shaw.ca> wrote:
> >>
> >> On 2023-08-18 07:09, Martin Wege via Cygwin wrote:
> >>> On Fri, Aug 18, 2023 at 10:44 AM Corinna Vinschen via Cygwin
> >>> <cygwin@cygwin.com> wrote:
> >>>>
> >>>> On Aug 17 20:49, Martin Wege via Cygwin wrote:
> >>>>> On Mon, Aug 14, 2023 at 10:56 PM Corinna Vinschen via Cygwin
> >>>>> <cygwin@cygwin.com> wrote:
> >>>>>> and the result is the same.  Note that Cygwin supports MSFT NFSv3 but
> >>>>>> not CITI NFSv4.1 internally.  No gurantee that Cygwin always does what
> >>>>>> is necessary for that other NFS.
> >>>>>
> >>>>> 1. How does Cygwin detect whether something is a MSFT NFSv3, or not?
> >>>>> Cygwin /bin/mount lists the CITI NFSv4.1 as 'nfs', so there *IS*
> >>>>> something which detects that?
> >>>>
> >>>> The filesystem name returned by NtQueryVolumeInformationFile is "NFS".
> >>>> If any other NFS returns the same filesystem name, it will be treated
> >>>> just like MSFT NFSv3.
> >>>>
> >>>>> 2. Are Cygwin soft link handing depend on MSFT NFSv3 or not, i.e. does
> >>>>> the Cygwin soft link code behave differently for MSFT NFSv3 file
> >>>>> systems?
> >>>>
> >>>> Yes.  NFS doesn't support symlink creation and symlink reading via
> >>>> the usual functions, because Windows symlinks are created as reparse
> >>>> points.  NFS doesn't support reparse points.  So the developers of
> >>>> the MSFT NFS client had to invent their own way to create and
> >>>> read NFS symlinks:
> >>>>
> >>>> https://sourceware.org/git/?p=newlib-cygwin.git;a=blob;f=winsup/cygwin/path.cc;hb=HEAD#l1719
> >>>>
> >>>> https://sourceware.org/git/?p=newlib-cygwin.git;a=blob;f=winsup/cygwin/path.cc;hb=HEAD#l2750
> >>>>
> >>>>> 3. Does Cygwin implement the pathconf() api?
> >>>>
> >>>> Yes.  Surprisingly, you can check this yourself by just calling the
> >>>> function and trying to compile your code.
> >>>
> >>> Apologies, how do we say in German? "Ich sollte meine Frage konkretisieren:"
> >>>
> >>> Does the Cygwin implementation of pathconf() support query data of the
> >>> underlying filesystem based on data from the kernel, as UNIX does? So
> >>> pathconf() returns different values for NTFS, ReFS, or Windows builtin
> >>> NFSv3?
> >>>
> >>> I am asking, because as far as I know the Linux implementation is not
> >>> a syscall, and instead glibc guesses values based on builtin static
> >>> data, and whatever fstatfs() has to offer. Compared to that UNIX
> >>> (Solaris, AIX, HPUX, ...) have pathconf() as a syscall, and actually
> >>> ask the filesystem itself.
> >>
> >> Many library functions are implemented as documented either in the Cygwin
> >> packages cygwin-doc and man-pages-posix available for installation; and use as
> >> e.g. `man 3p fpathconf`, also available online at:
> >> https://pubs.opengroup.org/onlinepubs/9699919799/functions/fpathconf.html or
> >> https://man7.org/linux/man-pages/man3/fpathconf.3p.html
> >> and for comparison and reference we make Cygwin package man-pages-linux
> >> available for installation; and use as e.g. `man -m linux 3 fpathconf`, also
> >> available online at:
> >>
> >>          https://man7.org/linux/man-pages/man3/fpathconf.3.html
> >>
> >> suggestions for setup are in the package announcements made every 9-12 weeks
> >> when the latest Linux man-pages package is released and updated on Cygwin.
> >>
> >> Please also note that the getconf(1) program is installed as part of Cygwin and
> >> can access f/pathconf variables associated with a pathname argument, as shown in
> >> getconf(1) `man 1 getconf` and getconf(1p) `man 1p getconf`.
> >
> > Thanks, but my question was about the Cygwin *implementation*: Does it
> > distinguish between NTFS, REFS, FAT, NFS? Does it use data obtained
> > from the Windows kernel at runtime, or does it rely on static data
> > compiled into the cygwin.dll library?
>
> My suggestion was to encourage you to try out the command on the relevant
> filesystems, or feel free to check out the repo and the implementation.

Where in the git is the implementation of pathconf()?

Thanks,
Martin