[5758] in Athena Bugs
A bug with AFS on the PMAX
daemon@ATHENA.MIT.EDU (geoff@ATHENA.MIT.EDU)
Fri Aug 17 18:52:46 1990
From: geoff@ATHENA.MIT.EDU
To: bugs@ATHENA.MIT.EDU
Cc: geoff@ATHENA.MIT.EDU
Date: Fri, 17 Aug 90 18:52:21 EDT
Program with which you had the problem: test program supplied below.
Name of person who discovered the bug:
Their MIT phone number:
Their MIT address:
Their Athena Login ID:geoff
Name of consultant reporting bug:
------------------------------------------------------------------------
A brief synopsis of the problem: seeking to end of file by using a 3rd
argument of "2" (relative to EOF) to lseek or fseek on a file accessed
via AFS on a PMAX is equivalent to using a 3rd argument of "0"
(relative to start of file).
------------------------------------------------------------------------
Please describe the problem in detail (mention any necessary files or
commands that may be involved, on which machine the bug happened, and what
the program did that was wrong): running the test program and then
catting temp.line will produce this output normally:
first line of text
second line
but when run on an AFS file system on a PMAX (e.g. hodge), produces
this output:
second line
f text
------------------------------------------------------------------------
Repeat by (please enter a set of commands which will allow us to
repeat the bug):
rlogin hodge
cd /tmp
/afs/sipb/user/geoff/decmipsbin/afs; cat temp.line
cd /afs/sipb/user/$USER # or some other AFS-mounted directory
/afs/sipb/user/geoff/decmipsbin/afs; cat temp.line
# note the differences in output
------------------------------------------------------------------------
Fix (if you know what it is): sorry.
--- test program follows ---
/*
* demo AFS bug: lseek(f,o,2)==lseek(f,o,0) /Geoff Collyer
* run this program, then "cat temp.line" and note the garble.
*/
#include <stdio.h>
#define TEMPFILE "temp.line" /* in current dir. to ease use */
#define LINE1 "first line of text\n"
#define LINE2 "second line\n"
#define STRLEN(s) (sizeof(s) - 1)
#ifndef SEEK_SET
#define SEEK_SET 0
#define SEEK_END 2
#endif
/* imports */
extern long lseek();
main()
{
register int fd;
fd = creat(TEMPFILE, 0666);
if (fd < 0) {
perror(TEMPFILE);
exit(1);
} else
(void) close(fd);
fd = open(TEMPFILE, 2); /* read/write */
if (fd < 0) {
perror(TEMPFILE);
exit(1);
}
if (write(fd, LINE1, STRLEN(LINE1)) != STRLEN(LINE1) ||
lseek(fd, 0L, SEEK_END) < 0 || /* no-op, in theory */
write(fd, LINE2, STRLEN(LINE2)) != STRLEN(LINE2) ||
close(fd) < 0)
fprintf(stderr, "error writing %s\n", TEMPFILE);
exit(0);
}
