Re: [PATCH 8/8 v2] xfs/189: systemd monitoring of /etc/fstab sucks

["Darrick J. Wong" <djwong@kernel.org>]

On Fri, Jun 03, 2022 at 11:54:13AM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> On a recently upgraded system, xfs/189 still works just fine, but
> every test run after it now gets spammed from mount/systemd
> like so:
> 
> xfs/189 [not run] noattr2 mount option not supported on /dev/vdc
> xfs/190 1s ... mount: (hint) your fstab has been modified, but systemd still uses
>        the old version; use 'systemctl daemon-reload' to reload.
>  1s
> xfs/192 3s ... mount: (hint) your fstab has been modified, but systemd still uses
>        the old version; use 'systemctl daemon-reload' to reload.
>  2s
> xfs/193 2s ... mount: (hint) your fstab has been modified, but systemd still uses
>        the old version; use 'systemctl daemon-reload' to reload.
>  2s
> xfs/194 1s ... mount: (hint) your fstab has been modified, but systemd still uses
>        the old version; use 'systemctl daemon-reload' to reload.
> 
> This is because xfs/189 modifies /etc/fstab during the test, then
> restores it to it's original condition so there's nothing to update.
> However, systemd is sees that the mtime of /etc/fstab has changed,
> and assumes they sky has fallen and so everything must be reloaded
> from scratch to silence the unnecessary "hint".
> 
> We can avoid this clumsiness by capturing the mtime of /etc/fstab
> before we modify it, and restore it afterwards and that means
> systemd doesn't even notice that we've being playing around with
> /etc/fstab.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> V2:
> - use systemctl daemon-reload instead of mtime futzing as Darrick
>   suggested.

Looks good,
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> 
>  tests/xfs/189 | 26 +++++++++++++++++++++++++-
>  1 file changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/tests/xfs/189 b/tests/xfs/189
> index e601881a..bc7ccca5 100755
> --- a/tests/xfs/189
> +++ b/tests/xfs/189
> @@ -32,6 +32,23 @@
>  #
>  # <---- Normal programming is resumed ---->
>  #
> +# <---- Bbbzzzzzzztttt ---->
> +#
> +# < systemd enters the chat >
> +#
> +# xfs/189 [not run] noattr2 mount option not supported on /dev/vdc
> +# xfs/190 1s ... mount: (hint) your fstab has been modified, but systemd still uses
> +#        the old version; use 'systemctl daemon-reload' to reload.
> +#  1s
> +#  xfs/192 3s ... mount: (hint) your fstab has been modified, but systemd still uses
> +#        the old version; use 'systemctl daemon-reload' to reload.
> +#
> +# mount/systemd sees that /etc/fstab has changed (because mtime changed)
> +# and so it whines that systemd needs updating on every mount from this point
> +# onwards. Yes, that's totally obnoxious behaviour from mount/systemd but we
> +# have to work around it.
> +#
> +# < systemd leaves the chat >
>  #
>  . ./common/preamble
>  _begin_fstest mount auto quick
> @@ -190,6 +207,10 @@ ENDL
>  # Example fstab entry
>  # /dev/sdb2            /mnt/scratch1        xfs       defaults 0 0
>  #
> +# Note that to avoid mnt/systemd whining about /etc/fstab being modified, we
> +# need to ensure that it reloads it's state once we restore the fstab to
> +# original.
> +#
>  _add_scratch_fstab()
>  {
>  	# comment out any existing SCRATCH_DEV
> @@ -201,7 +222,7 @@ _add_scratch_fstab()
>  
>  _modify_scratch_fstab()
>  {
> -	opts=$1
> +	local opts=$1
>  
>  	# modify our fstab entry that we added
>  	# modify opts by looking for last word which has non-space chars
> @@ -215,6 +236,9 @@ _putback_scratch_fstab()
>  
>  	# remove the one we added at the end
>  	$SED_PROG -i "/# $tag/d" /etc/fstab
> +
> +	# stop mount/systemd whining that /etcfstab was changed.
> +	command -v systemctl > /dev/null 2>&1 && systemctl daemon-reload
>  }
>  
>  # Import common functions.
> -- 
> Dave Chinner
> david@fromorbit.com