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Groups > comp.os.linux.development.apps > #207

Re: mmap unuseable for interactive application?

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Peter <excessphase@gmail.com> writes:
> On Jul 18, 11:17 am, Rainer Weikusat <rweiku...@mssgmbh.com> wrote:
>> Rainer Weikusat <rweiku...@mssgmbh.com> writes:
>> > Peter <excessph...@gmail.com> writes:
>> >> On Jul 18, 7:42 am, Rainer Weikusat <rweiku...@mssgmbh.com> wrote:
>> >>> 'Again' -- the solution to your 'problem' is to use the existing
>> >>> system facilities (which have existed 'since a long time') to
>> >>> coordinate use of shared resources by independent applications and not
>> >>> to whine about the fact that a lot of filesystems exists which don't
>> >>> work like the Windows file system.
>>
>> >> OK -- educate me!
>> >> What are the "existing system facilities" to prevent users from
>> >> accessing some file?
>>
>> > cd /
>> > rm -rf *
>>
>> > There is still some chance that a user might manage to access one of
>> > his own files while deletion is in progress but since this won't be
>> > reproducible, you can afterwards claim that it didn't happen.
>>
>> For sake of completeness: Linux supports (and has supported for
>> years, I was already using this facility with 2.4) a mechanism called
>> 'leases' for regular files (documented in fcntl(2)) which can be used
>> by a process in order to get notified when an otherwise unrelated
>> process is about to gain write or read access to a file (meaning, has
>> just called open w/ a specific mode) or has made a truncate call
>> conflicting with the lease and while this doesn't provide 'exclusive
>> open' it could be used to adapt a memory mapping of some file some
>> other process just messed with.
>
>
> So if you're using this feature,
> you get on signal before instead of one after your file has been
> changed by somebody else.

Precisely: The kernel will notify an 'interested process' that a
write or read access to some file of interest is about to happen in
order to enable some kind of sensible reaction to that. This was
(AFAIK) added on behalf or by the Samba people, specifically in order
to help with 'file sharing for Windows clients' (and 'network
filesystems' in general).

> This sounds to me rather like an accident than the design of an
> engineer

The reason for this is that anything which wasn't designed by a
Microsoft employee appears to be wrong to you and vice versa.
But that's just a bad habit and perfectly curable.

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mmap unuseable for interactive application? Peter <excessphase@gmail.com> - 2011-07-16 16:23 -0700
  Re: mmap unuseable for interactive application? Richard Kettlewell <rjk@greenend.org.uk> - 2011-07-17 10:52 +0100
    Re: mmap unuseable for interactive application? pacman@kosh.dhis.org (Alan Curry) - 2011-07-17 20:59 +0000
      Re: mmap unuseable for interactive application? Peter <excessphase@gmail.com> - 2011-07-17 14:05 -0700
        Re: mmap unuseable for interactive application? Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-07-18 12:45 +0100
          Re: mmap unuseable for interactive application? Peter <excessphase@gmail.com> - 2011-07-18 07:30 -0700
            Re: mmap unuseable for interactive application? Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-07-18 15:42 +0100
              Re: mmap unuseable for interactive application? Peter <excessphase@gmail.com> - 2011-07-18 07:46 -0700
                Re: mmap unuseable for interactive application? Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-07-18 15:50 +0100
                Re: mmap unuseable for interactive application? Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-07-18 19:17 +0100
                Re: mmap unuseable for interactive application? Peter <excessphase@gmail.com> - 2011-07-18 12:49 -0700
                Re: mmap unuseable for interactive application? Peter <excessphase@gmail.com> - 2011-07-18 12:51 -0700
                Re: mmap unuseable for interactive application? Peter <excessphase@gmail.com> - 2011-07-18 13:08 -0700
                Re: mmap unuseable for interactive application? Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-07-18 22:24 +0100
                Re: mmap unuseable for interactive application? Peter <excessphase@gmail.com> - 2011-07-18 15:04 -0700
                Re: mmap unuseable for interactive application? Peter <excessphase@gmail.com> - 2011-07-18 15:21 -0700
                Re: mmap unuseable for interactive application? Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-07-19 13:59 +0100
              Re: mmap unuseable for interactive application? Peter <excessphase@gmail.com> - 2011-07-18 07:50 -0700
      Re: mmap unuseable for interactive application? Richard Kettlewell <rjk@greenend.org.uk> - 2011-07-18 10:59 +0100
        Re: mmap unuseable for interactive application? pacman@kosh.dhis.org (Alan Curry) - 2011-07-18 20:14 +0000
  Re: mmap unuseable for interactive application? Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-07-17 19:40 +0100
    Re: mmap unuseable for interactive application? Peter <excessphase@gmail.com> - 2011-07-17 14:11 -0700
      Re: mmap unuseable for interactive application? Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-07-18 12:46 +0100
    Re: mmap unuseable for interactive application? Peter <excessphase@gmail.com> - 2011-07-17 14:13 -0700
      Re: mmap unuseable for interactive application? Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-07-18 13:49 +0100
        Re: mmap unuseable for interactive application? Peter <excessphase@gmail.com> - 2011-07-18 07:37 -0700

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