Q's about IBM TSM (was Re: HEADSUP: ibcs2 and svr4 compatheaded for history)

[Per Kristian Hove]

[Daniel O'Connor, 2004-06-30]

|  On Wed, 30 Jun 2004 01:11, Paul Mather wrote:
|  > having an empty or missing /compat/linux/etc/mtab file.  Creating a
|  > proper mtab file solves these problems.  One way to do this is via
|  > something like the following:
|  >
|  > 	sed 's/ufs/ext2/' < /etc/fstab > /compat/linux/etc/mtab
|  >
|  > That way, the Linux TSM "sees" your UFS partitions and will
|  > backup/restore to them.
|
|  I wonder if it could work with an LD_PRELOAD or some other linker trickery..

LD_PRELOADing ought to work. The attached file is an example library.
Compile with "gcc -o libmtab.so -shared -fpic libmtab.c" to test
(you'll probably have to add "-ldl" to compile it on Linux, if you
want to test TSM).

This is just a proof-of-concept; you'd probably want to substitue the
system() call with something sane, make sure you only s/ufs/ext2/ in
the third column, etc. Example:

   # cat /etc/mtab
   cat: /etc/mtab: No such file or directory
   # export LD_PRELOAD=$PWD/libmtab.so
   # cat /etc/mtab
   /dev/ad0s1a         /      ext2       rw                1    1
   /dev/ad0s1b         none   swap       sw                0    0
   /dev/ad0s1b         /tmp   mfs        rw,-s=1046528     0    0
   /dev/ad0s1e         /var   ext2       rw                1    2
   /dev/ad0s1f         /usr   ext2       rw                1    2
   /dev/acd0c          /cdrom cd9660     ro,nosuid,nodev,noauto 0    0
   /dev/ad0s2a         /work  ext2       rw                1    1

To be complete, the library should also work with relative pathnames.
Implementing that is left as an exercise for the reader. The example
library doesn't do that:

   # cd /etc; cat mtab
   cat: mtab: No such file or directory


-- 
Per Kristian Hove <Per.Hove at math.ntnu.no>
Chief engineer
Dept. of Mathematical Sciences
Norwegian University of Science and Technology
-------------- next part --------------
#include <stdio.h>
#include <dlfcn.h>
#include <string.h>
#include <limits.h>
#include <fcntl.h>

#ifndef RTLD_NEXT
#define RTLD_NEXT	  ((void *) -1l)
#endif

#define PATH_MTAB "/etc/mtab"

int open(const char *path, int oflag, ...) {
    static int             (*func) (const char *, int, ...);
    int                    fd, fdfstab;
    char tmpfile[] = "/tmp/mtab.XXXXXX";
    char cmd[80];

    if (!func)
	func = (int (*) (const char *, int, ...)) dlsym (RTLD_NEXT, "open");

    if (strcmp(path, PATH_MTAB))
	return func(path, oflag, 0600);

    if ((fd = mkstemp(tmpfile)) < 0) {
	perror("libmtab.so: mkstemp:");
    }
    sprintf(cmd, "sed 's/ufs/ext2/' < /etc/fstab > %s", tmpfile);
    system(cmd);
    unlink(tmpfile);
    return (fd);
}