Re: Struct with unaligned fields

From	James Kuyper <jameskuyper@verizon.net>
Newsgroups	comp.lang.c
Subject	Re: Struct with unaligned fields
Date	2013-08-23 16:15 -0400
Organization	Self
Message-ID	<5217C2F7.4040604@verizon.net> (permalink)
References	<kv5jvm$7mk$1@dont-email.me> <kv5vgt$cj2$1@dont-email.me> <kv7j0j$a96$1@dont-email.me> <kv7lcm$ll4$1@dont-email.me> <kv8clj$mn5$1@dont-email.me>

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On 08/23/2013 03:20 PM, James Harris wrote:
...
> From this and other comments you have made I think you may be thinking of 
> these awkward fields as being external to the running system - i.e. read it 
> once and then forget about the original. That is true of some. But others 
> may form elements of the running system. At least if there's a chance of a 
> user program accessing any one of these fields we've been talking about I 
> cannot just maintain my own copy until the whole thing is written back to 
> disk. If I did, user programs would see inconsistent values.

Reading the FAT and updating it should always be hidden from the
ordinary user by system routines of some kind, and those routines must
be carefully designed to coordinate with each other to avoid the
potential problems you're referring to. If you're writing some of that
system code, you need to think a lot more carefully about the design
than you have currently seem to have done. If you're not writing such
code, you should not be able to modify the real FAT, all you should be
able to modify is a copy of it, so the problem you're worried about
shouldn't be possible.

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Struct with unaligned fields "James Harris" <james.harris.1@gmail.com> - 2013-08-22 19:06 +0100
  Re: Struct with unaligned fields glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2013-08-22 18:18 +0000
  Re: Struct with unaligned fields James Kuyper <jameskuyper@verizon.net> - 2013-08-22 14:57 -0400
    Re: Struct with unaligned fields "James Harris" <james.harris.1@gmail.com> - 2013-08-22 21:05 +0100
      Re: Struct with unaligned fields James Kuyper <jameskuyper@verizon.net> - 2013-08-22 16:45 -0400
      Re: Struct with unaligned fields Keith Thompson <kst-u@mib.org> - 2013-08-22 15:12 -0700
    Re: Struct with unaligned fields glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2013-08-22 22:22 +0000
    Re: Struct with unaligned fields Les Cargill <lcargill99@comcast.com> - 2013-08-22 22:07 -0500
  Re: Struct with unaligned fields Stephen Sprunk <stephen@sprunk.org> - 2013-08-22 14:13 -0500
    Re: Struct with unaligned fields Les Cargill <lcargill99@comcast.com> - 2013-08-22 22:08 -0500
      Re: Struct with unaligned fields "James Harris" <james.harris.1@gmail.com> - 2013-08-23 09:36 +0100
        Re: Struct with unaligned fields Les Cargill <lcargill99@comcast.com> - 2013-08-23 12:48 -0500
    Re: Struct with unaligned fields "James Harris" <james.harris.1@gmail.com> - 2013-08-23 09:34 +0100
      Re: Struct with unaligned fields Stephen Sprunk <stephen@sprunk.org> - 2013-08-23 04:47 -0500
        Re: Struct with unaligned fields "James Harris" <james.harris.1@gmail.com> - 2013-08-23 15:31 +0100
          Re: Struct with unaligned fields Stephen Sprunk <stephen@sprunk.org> - 2013-08-23 13:31 -0500
            Re: Struct with unaligned fields "James Harris" <james.harris.1@gmail.com> - 2013-08-23 20:46 +0100
            Re: Struct with unaligned fields glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2013-08-23 20:48 +0000
  Re: Struct with unaligned fields Jorgen Grahn <grahn+nntp@snipabacken.se> - 2013-08-22 20:01 +0000
    Re: Struct with unaligned fields "James Harris" <james.harris.1@gmail.com> - 2013-08-23 12:54 +0100
      Re: Struct with unaligned fields Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-08-23 08:17 -0400
      Re: Struct with unaligned fields Jorgen Grahn <grahn+nntp@snipabacken.se> - 2013-08-23 20:00 +0000
      Re: Struct with unaligned fields Tim Rentsch <txr@alumni.caltech.edu> - 2013-08-24 16:50 -0700
  Re: Struct with unaligned fields "BartC" <bc@freeuk.com> - 2013-08-22 21:59 +0100
    Re: Struct with unaligned fields Keith Thompson <kst-u@mib.org> - 2013-08-22 15:02 -0700
    Re: Struct with unaligned fields Tim Rentsch <txr@alumni.caltech.edu> - 2013-08-24 16:42 -0700
  Re: Struct with unaligned fields Siri Cruise <chine.bleu@yahoo.com> - 2013-08-22 14:21 -0700
  Re: Struct with unaligned fields Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-08-22 17:23 -0400
    Re: Struct with unaligned fields "James Harris" <james.harris.1@gmail.com> - 2013-08-23 13:03 +0100
      Re: Struct with unaligned fields Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-08-23 08:43 -0400
        Re: Struct with unaligned fields "James Harris" <james.harris.1@gmail.com> - 2013-08-23 20:20 +0100
          Re: Struct with unaligned fields James Kuyper <jameskuyper@verizon.net> - 2013-08-23 16:15 -0400
          Re: Struct with unaligned fields Ian Collins <ian-news@hotmail.com> - 2013-08-24 11:47 +1200
            Re: Struct with unaligned fields "James Harris" <james.harris.1@gmail.com> - 2013-08-24 14:01 +0100
              Re: Struct with unaligned fields Robert Wessel <robertwessel2@yahoo.com> - 2013-08-24 14:26 -0500
                Re: Struct with unaligned fields Ian Collins <ian-news@hotmail.com> - 2013-08-25 08:55 +1200
                Re: Struct with unaligned fields Robert Wessel <robertwessel2@yahoo.com> - 2013-08-25 04:17 -0500
                Re: Struct with unaligned fields Ian Collins <ian-news@hotmail.com> - 2013-08-25 21:22 +1200
                Re: Struct with unaligned fields Stephen Sprunk <stephen@sprunk.org> - 2013-08-24 16:16 -0500
                Re: Struct with unaligned fields Robert Wessel <robertwessel2@yahoo.com> - 2013-08-25 04:43 -0500
                Re: Struct with unaligned fields David Thompson <dave.thompson2@verizon.net> - 2013-08-28 22:27 -0400
                Re: Struct with unaligned fields Stephen Sprunk <stephen@sprunk.org> - 2013-08-29 14:30 -0500
                Re: Struct with unaligned fields Robert Wessel <robertwessel2@yahoo.com> - 2013-08-29 16:41 -0500
      Re: Struct with unaligned fields "BartC" <bc@freeuk.com> - 2013-08-23 23:55 +0100
  Re: Struct with unaligned fields Les Cargill <lcargill99@comcast.com> - 2013-08-22 22:05 -0500
    Re: Struct with unaligned fields Stephen Sprunk <stephen@sprunk.org> - 2013-08-23 00:29 -0500
      Re: Struct with unaligned fields Les Cargill <lcargill99@comcast.com> - 2013-08-23 12:53 -0500
        Re: Struct with unaligned fields Stephen Sprunk <stephen@sprunk.org> - 2013-08-23 15:15 -0500
          Re: Struct with unaligned fields Les Cargill <lcargill99@comcast.com> - 2013-08-23 22:14 -0500
            Re: Struct with unaligned fields Ian Collins <ian-news@hotmail.com> - 2013-08-24 16:24 +1200
              Re: Struct with unaligned fields Les Cargill <lcargill99@comcast.com> - 2013-08-23 23:47 -0500
            Re: Struct with unaligned fields Keith Thompson <kst-u@mib.org> - 2013-08-24 01:16 -0700
              Re: Struct with unaligned fields Les Cargill <lcargill99@comcast.com> - 2013-08-24 09:45 -0500
                Re: Struct with unaligned fields Keith Thompson <kst-u@mib.org> - 2013-08-24 13:52 -0700
                Re: Struct with unaligned fields Tim Prince <tprince@computer.org> - 2013-08-24 17:07 -0400
                Re: Struct with unaligned fields Les Cargill <lcargill99@comcast.com> - 2013-08-24 16:35 -0500
                Re: Struct with unaligned fields Ian Collins <ian-news@hotmail.com> - 2013-08-25 09:51 +1200
                Re: Struct with unaligned fields Keith Thompson <kst-u@mib.org> - 2013-08-24 16:04 -0700
                Re: Struct with unaligned fields Les Cargill <lcargill99@comcast.com> - 2013-08-24 21:03 -0500
          Re: Struct with unaligned fields Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-08-24 08:22 -0400
  Re: Struct with unaligned fields Nobody <nobody@nowhere.com> - 2013-08-23 17:51 +0100
  Re: Struct with unaligned fields falk@rahul.net (Edward A. Falk) - 2013-08-24 01:43 +0000

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