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Re: file corruption during emacs build on XFS logical volume

To: Linux XFS <linux-xfs@xxxxxxxxxxx>
Subject: Re: file corruption during emacs build on XFS logical volume
From: Sean Neakums <sneakums@xxxxxxxx>
Date: Fri, 04 Jan 2002 18:28:10 +0000
In-reply-to: <6u666ikn5n.fsf@zork.zork.net> (Sean Neakums's message of "Fri, 04 Jan 2002 18:04:52 +0000")
Mail-followup-to: Linux XFS <linux-xfs@xxxxxxxxxxx>
References: <1010141444.1992.3.camel@pyewacket> <1010164935.1945.8.camel@UberGeek> <6u666ikn5n.fsf@zork.zork.net>
Sender: owner-linux-xfs@xxxxxxxxxxx
User-agent: Gnus/5.090004 (Oort Gnus v0.04) Emacs/21.1 (i386-debian-linux-gnu)
begin  Sean Neakums quotation:

> begin  Austin Gonyou quotation:
>
>> No, It does not guarantee. Also, if you're not on the same Inode the
>> file time is different, etc, it's possible to have different md5sums. A
>> basic size and file comparison is probably best for what you want to do.
>
> The md5sum of a file is based on its contents only.  The inode has
> nothing to do with it.
>
>> Something you can do to test what I'm talking about is copy each of your
>> dumps to another name, binfilexyz.1 or something, then compare it's
>> md5sum against the original. Those should be the only time they match.  
>
> I'm not sure exaclty what you mean by this.  The name of the file is
> irrelevant in the computation of the md5sum.

In Emacs' case, there's a niggle with this: if there's already an
emacs-21.1.1 file there, it'll dump as emacs-21.1.2, and the dumped
file will have that version embedded in it.  The script I was using to
generate the ms5sum was aware of this, and deleted the dumped files
before each dump, so that the dump always happened to the name
emacs-21.1.1.  However, there  is a variable, emacs-build-time, which
contains the exact time the dump occurred.  So md5sums are no use anyway.

Funnily, the last file dump I did worked correctly at the time, but is
now segfaulting, some hours later.

I was doing the dumps while running three instances of this program,
which I hacked up in a hurry, to generate lots of dirty pages and
actual I/O:  http://zork.net/~sneakums/io-test.c

I wonder if the pages that are modified by the dump are not being
written to disk correctly?  This last dump was in a D state for a few
minutes while the three io-test instances were running, but it did
complete and seemingly start up correctly a few minutes after I killed
them.

-- 
 /////////////////  |                  | The spark of a pin
<sneakums@xxxxxxxx> |  (require 'gnu)  | dropping, falling feather-like.
 \\\\\\\\\\\\\\\\\  |                  | There is too much noise.


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