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From: rog@speech.kth.se (Roger Lindell)
Newsgroups: comp.sys.apollo
Subject: Re: Perl op.stat failure
Message-ID: <rog.659804117@nebula>
Date: 28 Nov 90 15:36:45 GMT
References: <3071@nosc.NOSC.MIL> <1219@digi.lonestar.org> <1249@digi.lonestar.org>
Sender: news@kth.se  (News Administrator)
Organization: Royal Institute of Technology
Lines: 90

kgallagh@digi.lonestar.org (Kevin Gallagher) writes:

>I tried modifying the op.stat perl script by adding the line

>    close(foo);

>immediately before the invocation of stat.  Now, it did not matter if I ran it
>from my node or some other node, stat always returned 0 as the number of
>links.

[Stuff deleted]

>If I modified the perl op.stat script NOT to open the file before invoking the
>stat command, it always returned 0 links, no matter where I was logged in.

>It appears that, on the Apollo, perl's stat only works correctly if the file
>is opened AND is located on a a disk in the same node where the script is
>executed.  But this is a preliminary guess.  I did not check if the two nodes
>I used were on the same or different rings.  Maybe it works OK if the nodes
>are in the same ring.  But I am puzzled why perl stat always returns 0 links
>when the file is not opened.  Anyway, the problem needs further investigation.
>I briefly searched the perl source this evening and suspect that the file
>doio.c handles the perl stat processing.

>Anyone got a clue what is going on here?

The problem is that perl's stat() is the equivalent to Apollo's fstat() and
to use this function you need a file descriptor as an argument. This means that
the file must be open when you do a stat in perl.

I wrote a small C-program which uses fstat() and reports the number of links
to a file. The source code follows:

	#include <stdio.h>
	#include <sys/file.h>
	#include <sys/types.h>
	#include <sys/stat.h>

	void main(int argc, char **argv)
	{

	  int file_d ;
	  struct stat stat_buffer ;

	  if (argc == 2)
	  {
	    file_d = open(argv[1],O_CREAT|O_RDWR|O_APPEND,0644) ;
	    fstat(file_d,&stat_buffer) ;
	    printf("Number of hard links = %d\n",(int)stat_buffer.st_nlink) ;
	    close(file_d) ;
	  }
	}

When I run this program, and as input gives the name of a nonexistent file, I get
the answer
	Number of hard links = 0
if the disk, on which the file gets created, is not local. If on the other hand I
run this program on the machine that has the disk, I get
	Number of hard links = 1

If I run the program, and as input gives the name of an existing file, I get
the answer
	Number of hard links = 1
independently of if the file is on a local disk or not.

You can try this with perl's op.stat program, add these two lines before the first
open
	open(foo, ">Op.stat.tmp");
	close(foo);

If you do this and then run the op.stat program it will report that everthing is OK,
but since there is an unlink instruction preceding the original open I don't think
that my fix is a "supported" fix.

So the problem seems to be with Apollo's fstat().
Is this a genuine Apollo bug or is this something that is allowed by BSD UNIX?
Why I ask this is because if you read the man page for fstat and look at the BUGS
section it says: 
     Applying fstat to a socket (and thus to a pipe) returns a zeroed buffer,
     except for the blocksize field, and a unique device and inode number.

Roger Lindell



--
Roger Lindell			rog@speech.kth.se
Phone: +46 8 790 75 73		Fax: +46 8 790 78 54
Dept. of Speech Communication and Music Acoustics
Royal Institute of Technology	Sweden