From: Martin Wege <martin.l.wege@gmail.com>
To: "cygwin@cygwin.com" <cygwin@cygwin.com>,
Corinna Vinschen <corinna-cygwin@cygwin.com>
Subject: Re: How to fix |mkfifo()| failure if |pathname| is on NFS ? / was: Re: [EXTERNAL] Re: mkfifo: cannot set permissions of 'x.fifo': Not a directory
Date: Sat, 26 Aug 2023 19:58:17 +0200 [thread overview]
Message-ID: <CANH4o6PWnPEcadHX9T1TwaS1gPrT-bN3Yy8av4k2Mjc0WAR7ZA@mail.gmail.com> (raw)
In-Reply-To: <CANH4o6MFsCY4awWmo5vcow4_jZKnkoc8A1C72Ub=2OBuyCkRqA@mail.gmail.com>
On Thu, Aug 24, 2023 at 6:45 PM Martin Wege <martin.l.wege@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
next prev parent reply other threads:[~2023-08-26 17:58 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-07 14:42 Martin Wege
2023-08-07 18:26 ` Brian Inglis
2023-08-07 19:14 ` Corinna Vinschen
2023-08-07 21:14 ` Martin Wege
2023-08-08 8:20 ` Corinna Vinschen
2023-08-08 19:38 ` Martin Wege
2023-08-09 8:01 ` Corinna Vinschen
2023-08-09 9:12 ` Martin Wege
2023-08-09 9:56 ` Corinna Vinschen
2023-08-10 12:49 ` Martin Wege
2023-08-18 4:02 ` Martin Wege
2023-08-18 8:34 ` Corinna Vinschen
2023-08-18 13:14 ` Martin Wege
2023-08-21 4:49 ` Cedric Blancher
2023-08-21 8:37 ` Corinna Vinschen
2023-08-22 14:52 ` [EXTERNAL] " Lavrentiev, Anton (NIH/NLM/NCBI) [C]
2023-08-22 23:05 ` How to fix |mkfifo()| failure if |pathname| is on NFS ? / was: " Roland Mainz
2023-08-24 16:45 ` Martin Wege
2023-08-25 4:25 ` Cedric Blancher
2023-08-26 17:58 ` Martin Wege [this message]
2023-08-25 12:18 ` Corinna Vinschen
2023-08-25 12:25 ` Corinna Vinschen
2023-08-26 11:26 ` Cedric Blancher
2023-08-26 14:15 ` Corinna Vinschen
2023-08-26 17:40 ` Martin Wege
2023-08-26 19:16 ` Brian Inglis
2023-08-25 15:14 ` Roland Mainz
2023-08-26 11:27 ` Cedric Blancher
2023-08-25 23:21 ` Lavrentiev, Anton (NIH/NLM/NCBI) [C]
2023-08-26 14:28 ` Corinna Vinschen
2023-08-26 14:39 ` Lavrentiev, Anton (NIH/NLM/NCBI) [C]
2023-08-26 17:44 ` Documenting Cygwin on NFS, no longer only exchange-medium! " Martin Wege
2023-08-26 19:16 ` Brian Inglis
2023-08-27 12:35 ` Corinna Vinschen
2023-08-28 5:35 ` Cedric Blancher
2023-08-28 10:02 ` Corinna Vinschen
2023-08-28 11:41 ` Joshuah Hurst
[not found] ` <14a692f6-7244-4a7e-a69b-d14521fb01e8@secure-endpoints.com>
2023-08-23 17:39 ` Lavrentiev, Anton (NIH/NLM/NCBI) [C]
2023-08-24 5:28 ` Cedric Blancher
2023-08-24 16:40 ` Martin Wege
2023-08-21 12:12 ` Martin Wege
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