linux-ext4 - Re: [GIT PULL] ext4 bug fixes for 4.2-rc2

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Date:	Sun, 12 Jul 2015 10:20:56 +0200
From:	Jörg-Volker Peetz <jvpeetz@....de>
To:	Theodore Ts'o <tytso@....edu>
CC:	linux-ext4@...r.kernel.org
Subject: Re: [GIT PULL] ext4 bug fixes for 4.2-rc2

Theodore Ts'o wrote on 07/11/2015 23:06:
> On Sat, Jul 11, 2015 at 02:07:10PM +0200, Jörg-Volker Peetz wrote:
<snip>
> I knew about the fact that you couldn't disable lazytime.  The issue
> is that nolazytime is getting intercepted by the 2.26.2 version of
> mount, so ext4 never sees it.  But if we interpret the lack of the
> lazytime flag in the mount flags passed in from the system call, then
> we would *always* disable the lazytime flag if the file system is
> remounted using a pre-2.26.2 version of mount.  Since a huge number of
> Ubuntu LTS and Debian stable users (and probably a bunch of older
> Fedora users as well) will be using an older version of mount, I
> decided that best compromise is was to allow lazytime to be enabled
> using a 2.26.2+ version of mount via remount, but not to allow
> lazytime to be disabled.  With a pre-2.26.2 version of mount, you'll
> be able to enable or disable lazytime.
> 
O.k. Thanks for the explanation.

> As far as switching atime modes using remount, this is working for me.
> I'm testing with both a 2.25.2 version of mount as found in Debian
> Jessie, as well as 2.26.2 version of mount using Debian Stretch.  
> 
> 
> The issue not being able to change the atime, relatime, and noatime
> flags is a similar issue.  In pre-2.26.2 versions of mount, the atime,
> relatime, and noatime strings were passed to the kernel, which would
> then interpret the strings and the manipulate the 
> 
> 
>> # strace -o /tmp/st mount -o remount,relatime /home
>> # grep ^mount /tmp/st
>> mount("/dev/sda2", "/home", 0x1543780, MS_REMOUNT|MS_RELATIME|MS_NOATIME,
>> "nobarrier,errors=remount-ro") = 0
> 
> "MS_REMOUNT|MS_RELATIME|MS_NOATIME" looks wrong.  Here's what I'm
> seeing on my system:
> 
> # strace -o /tmp/st mount -o remount,relatime /dev/sda3
> # grep sda3 /proc/mounts
> /dev/sda3 / ext4 rw,lazytime,relatime,errors=remount-ro,data=ordered 0 0
> # grep MS_REMOUNT /tmp/st
> mount("/dev/sda3", "/", 0x1148230, MS_REMOUNT|MS_RELATIME|0x2000000, "errors=remount-ro") = 0
> # strace -o /tmp/st mount -o remount,noatime /dev/sda3
> # grep sda3 /proc/mounts
> /dev/sda3 / ext4 rw,lazytime,noatime,errors=remount-ro,data=ordered 0 0
> # grep MS_REMOUNT /tmp/st
> mount("/dev/sda3", "/", 0x1458230, MS_REMOUNT|MS_NOATIME|0x2000000, "errors=remount-ro") = 0
> # mount --version
> mount from util-linux 2.26.2 (libmount 2.26.0: selinux, assert, debug)
> # dpkg -l mount
> Desired=Unknown/Install/Remove/Purge/Hold
> | Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
> |/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
> ||/ Name                Version        Architecture   Description
> +++-===================-==============-==============-===========================================
> ii  mount               2.26.2-6       amd64          Tools for mounting and manipulating filesys
> 
>     				       		      - Ted
On my Debian stretch/sid systems there is:

# mount --version
mount from util-linux 2.26.2 (libmount 2.26.0: selinux, assert, debug)

# dpkg -l mount libmount1 libblkid1 libc6 libselinux1
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name           Version      Architecture Description
+++-==============-============-============-=================================
ii  libblkid1:amd6 2.26.2-6     amd64        block device id library
ii  libc6:amd64    2.19-18      amd64        GNU C Library: Shared libraries
ii  libmount1:amd6 2.26.2-6     amd64        device mounting library
ii  libselinux1:am 2.3-2+b1     amd64        SELinux runtime shared libraries
ii  mount          2.26.2-6     amd64        Tools for mounting and manipulati

I'm using kernel 4.1.2 plus two of your patches, but get the same output on a
system with a standard Debian kernel linux-image-4.0.0-2-amd64.
-- 
Regards,
Jörg.

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