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Re: May device identifier be changed without reboot?

Cross-posted to 2 groups.

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"Richard Kettlewell"  wrote in message 
news:87ehvdjicl.fsf@araminta.anjou.terraraq.org.uk...

> Alex Vinokur <alex.vinokur@gmail.com> writes:
>> May 'st.st_dev of the same file (that wasn't removed)' be changed
>> between reboots?
>
> Yes, provided you're prepared to stretch "not removed" a bit.
>
> Suppose the file is on one of several external USB hard disks.  Unmount
> and detach them all, then re-attach them in a different order.  What was
> formerly /dev/sdc may now be /dev/sdd, and so on.  The st_dev of the
> file will differ accordingly.



Thanks.

Does it mean the ftok() function has bug in design on Linux?

-------------------------------------------

From 
http://groups.google.com/group/comp.unix.programmer/msg/9dc05598257bdbb6

CentOS glibc-2.5-65.src.rpm source code:
/* sysvipc/ftok.c */
key_t
ftok (pathname, proj_id)
     const char *pathname;
     int proj_id;
{
  struct stat64 st;
  key_t key;


  if (__xstat64 (_STAT_VER, pathname, &st) < 0)
    return (key_t) -1;


  key = ((st.st_ino & 0xffff) | ((st.st_dev & 0xff) << 16)
         | ((proj_id & 0xff) << 24));


  return key;



}
------------------------------------------

==========================================
From http://linux.about.com/library/cmd/blcmdl3_ftok.htm

The resulting value is the same for all pathnames that name the same file, 
when the same value of proj_id is used.
==========================================

Alex

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Thread

[Linux] May device identifier be changed without reboot? Alex Vinokur <alex.vinokur@gmail.com> - 2012-01-04 20:53 -0800
  Re: [Linux] May device identifier be changed without reboot? Rainer Weikusat <rweikusat@mssgmbh.com> - 2012-01-05 16:01 +0000
    Re: [Linux] May device identifier be changed without reboot? Barry Margolin <barmar@alum.mit.edu> - 2012-01-05 21:24 -0500
      Re: [Linux] May device identifier be changed without reboot? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2012-01-06 07:02 +0000
        Re: [Linux] May device identifier be changed without reboot? "Alex Vinokur" <alexvn@users.sourceforge.net> - 2012-01-06 10:21 +0200
        Re: May device identifier be changed without reboot? Alex Vinokur <alex.vinokur@gmail.com> - 2012-01-06 00:14 -0800
          Re: May device identifier be changed without reboot? Richard Kettlewell <rjk@greenend.org.uk> - 2012-01-06 09:22 +0000
            Re: May device identifier be changed without reboot? "Alex Vinokur" <alexvn@users.sourceforge.net> - 2012-01-06 11:34 +0200
              Re: May device identifier be changed without reboot? Barry Margolin <barmar@alum.mit.edu> - 2012-01-06 07:57 -0500
              Re: May device identifier be changed without reboot? Kaz Kylheku <kaz@kylheku.com> - 2012-01-06 16:06 +0000
                Re: May device identifier be changed without reboot? Alex Vinokur <alex.vinokur@gmail.com> - 2012-01-06 10:17 -0800
  Re: [Linux] May device identifier be changed without reboot? Tim Roberts <timr@probo.com> - 2012-01-05 22:43 -0800

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