dear nick,
i have tried a sync after the remount, but that did not help. what helped
is dropping the cache by echoing 3 to /proc/sys/vm/drop_caches, but this
still didnt solve the problem in 100%, only in 95% of the cases.
But when i read the device with
# dd if=/dev/ram0 iflag=direct ...
then it worked. I think this bypassed some caches, and thus read the
actual data.
But a sad result is that I experienced with it, and only with ramdisk does
it work as expected. for example with a logical volume it behaves in the
wrong way.
thanks in advance,
Kojedzinszky Richard
TvNetWork Nyrt.
E-mail: krichy (at) tvnetwork [dot] hu
PGP: 0x24E79141
Fingerprint = 6847 ECFF EF58 0C09 18A5 16CF 270F 0C6F 24E7 9141
On Wed, 15 Oct 2008, Nick Piggin wrote:
Date: Wed, 15 Oct 2008 06:16:44 +0200
From: Nick Piggin <npiggin@xxxxxxx>
To: Richard Kojedzinszky <krichy@xxxxxxxxxxxx>
Cc: linux-ext4@xxxxxxxxxxxxxxx
Subject: Re: minix/ext2 + rd problem
Hi,
Thanks for reporting this.
On Tue, Oct 14, 2008 at 04:43:55PM +0200, Richard Kojedzinszky wrote:
dear all,
I got an embedded system, where I use ramdisk, minix on it as a filesystem
for /etc. With kernels 2.4 and with 2.6.19 kernels also, the following
code did exactly what i wanted, creating an image of the /etc without
unmounting it:
# mount -o remount,ro /etc
# cat /dev/ram0 > /tmp/image
# mount -o remount,rw /etc
And then I had a consistent image from /etc in /tmp/image.
This worked still with kernel version 2.6.23.14, but nowadays i upgraded
to 2.6.26.2, and noticed that the little code didnt work anymore. I wrote
a simple test script for checking, and reproducing the issue, which is
also attached. Unfortunately this does not work with ext2 also.
my linux version is:
Linux version 2.6.26 (root@xxxxxxxxxxxxxxxxxxx) (gcc version 4.2.4 (Debian
4.2.4-3)) #27 SMP PREEMPT Tue Oct 14 15:19:30 CEST 2008
i use debian lenny/sid.
Were there any intended change that made this behaviour change or was it
by an accident?
That shouldn't have been changed on purpose, unless it is doing something
funny that worked by accident before.
/dev/ram will behave much more like any other block device now (with brd)
wheras previously it was probably more coherent between filesystem and
block device node. Hmm, does all the filesystems cache get written back
before remount ro return?
Could you try sticking a sync after remount,ro?
Thanks,
Nick
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