On Thu, Aug 24, 2023 at 6:45 PM Martin Wege <martin.l.w...@gmail.com> wrote:
>
> On Wed, Aug 23, 2023 at 1:06 AM Roland Mainz via Cygwin
> <cygwin@cygwin.com> wrote:
> >
> > On Tue, Aug 22, 2023 at 4:52 PM Lavrentiev, Anton (NIH/NLM/NCBI) [C]
> > via Cygwin <cygwin@cygwin.com> wrote:
> > > > FIFOs which don't make *any* sense
> > > > ... FWIW, a remote NFS fileystem.
> > >
> > > I got an impression that the OP is trying to deploy something (maybe the
> > > entire Cygwin) onto an
> > > NFS share. So the named FIFO "file" is also created in there.
> >
> > I agree with that impression. This is basically what large sites
> > (universities etc) do with UNIX and Linux: The machines mount an
> > user's ${HOMR} directory via automounter over NFS, and users are
> > discouraged (e.g. grumpy admin visiting you in person, blocking all
> > escape routes... =:-) ) from using the machine's local filesystems (in
> > Cygwin's case that includes "C:"!).
> >
> > In that case people want to use |mkfifo()|/|mkfifoat()| and/or
> > /usr/bin/mkfifo in their home directory, and don't expect that it does
> > not work.
> >
> > But that is what happens on Cygwin 3.4.8 right now, if someone tries
> > to do a |mkfifo()| on a NFS home directory (tested with MS NFSv3 and
> > CITI NFSv4 clients):
> > |mkfifo()| succeeds, but the resulting inode is *NOT* a FIFO as requested
> >
> > Example (/cygdrive/h/ is my home directory shared from my Linux machine):
> > ---- snip ----
> > roland_mainz@winkrakra1 /cygdrive/h/work/cygwin_mkfifo_on_nfs
> > $ uname -a
> > CYGWIN_NT-10.0-19045 winkrakra1 3.4.8-1.x86_64 2023-08-17 17:02 UTC
> > x86_64 Cygwin
> >
> > roland_mainz@winkrakra1 /cygdrive/h/work/cygwin_mkfifo_on_nfs
> > $ mount
> > C:/cygwin64/bin on /usr/bin type ntfs (binary,auto)
> > C:/cygwin64/lib on /usr/lib type ntfs (binary,auto)
> > C:/cygwin64 on / type ntfs (binary,auto)
> > C: on /cygdrive/c type ntfs (binary,posix=0,user,noumount,auto)
> > H: on /cygdrive/h type nfs (binary,posix=0,user,noumount,auto)
> >
> > roland_mainz@winkrakra1 /cygdrive/h/work/cygwin_mkfifo_on_nfs
> > $ ls -l
> > total 1
> > -rw-rw-rw- 1 Unix_User+0 Unix_Group+0 330 Aug 22 23:58
> > cygwin_mkfifo_on_nfs.c
> >
> > roland_mainz@winkrakra1 /cygdrive/h/work/cygwin_mkfifo_on_nfs
> > $ cat -n cygwin_mkfifo_on_nfs.c
> > 1 #include <stdlib.h>
> > 2 #include <stdio.h>
> > 3 #include <stdio.h>
> > 4 #include <errno.h>
> > 5 #include <sys/types.h>
> > 6 #include <sys/stat.h>
> > 7
> > 8 int main(int ac, char *av[])
> > 9 {
> > 10 (void)puts("# start");
> > 11
> > 12 if
> > (mkfifo("/cygdrive/h/work/cygwin_mkfifo_on_nfs/myfifo.fifo", 0) != 0)
> > 13 perror("mkfifo failed");
> > 14 (void)puts("# done.");
> > 15 return EXIT_SUCCESS;
> > 16 }
> > 17
> >
> > roland_mainz@winkrakra1 /cygdrive/h/work/cygwin_mkfifo_on_nfs
> > $ gcc -g cygwin_mkfifo_on_nfs.c
> >
> > roland_mainz@winkrakra1 /cygdrive/h/work/cygwin_mkfifo_on_nfs
> > $ ./a
> > # start
> > # done.
> >
> > roland_mainz@winkrakra1 /cygdrive/h/work/cygwin_mkfifo_on_nfs
> > $ ls -l
> > total 68
> > -rwxr-xr-x 1 Unix_User+0 Unix_Group+0 66951 Aug 23 00:12 a.exe
> > -rw-rw-rw- 1 Unix_User+0 Unix_Group+0 330 Aug 22 23:58
> > cygwin_mkfifo_on_nfs.c
> > lrwxrwxrwx 1 Unix_User+0 Unix_Group+0 11 Aug 23 00:12 myfifo.fifo
> > -> ':\0:c4:1000'
> >
> > roland_mainz@winkrakra1 /cygdrive/h/work/cygwin_mkfifo_on_nfs
> > $ cat <myfifo.fifo
> > -bash: myfifo.fifo: No such file or directory
> > ---- snip ----
> >
> > Note that Cygwin does not interpret the file |myfifo.fifo| as FIFO,
> > instead it comes back as a symlink "myfifo.fifo -> ':\0:c4:1000'".
> >
> > AFAIK there are (at least) these two options to fix the problems:
> > 1. Check whether the filesystem for the fifos path is NFS
> > (cgywin.dll's |fs.fs_is_nfs()|), and if it is a symlink check if it
> > starts with ':\0:c4:' (assuming "c4" is the prefix for inodes created
> > with |mkfifo()|). If this condition is |true|, then cygwin |stat()|,
> > |open()| etc. should treat this inode as FIFO.
> > 2. Check whether the filesystem for the fifos path is NFS
> > (cgywin.dll's |fs.fs_is_nfs()|), and then just refuse |mkfifo()| with
> > |ENOSYS| (not implemented)
> >
> > Better algorithm for [1] might be to check whether the inode is a
> > symlink, and then do a |fs.fs_is_nfs()| on the symlinks |pathname|,
> > assuming this is more performant.
>
> We would like to see option 1 implemented, maybe as an option in the
> CYGWIN environment variable
> (CYGWIN=nfs_emulate_dev_special_files_as_symlink ?)
One problem I see is how we can set machine-wide defaults, as the
CYGWIN variable is only inherited from process to process, and
/usr/bin/env - myprog will start myprog with an empty environment.
So if there is no way to set machine-wide defaults, I would prefer to
have the nfs_emulate_dev_special_files_as_symlink enabled by default.
Thanks,
Martin
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