On Tue 24-04-18 11:50:28, Joe Lawrence wrote:
> On 04/23/2018 10:43 AM, Joe Lawrence wrote:
> > On Fri, Apr 20, 2018 at 02:56:05PM +0200, Libor Pechacek wrote:
> >> On Thu 12-04-18 10:54:31, Joe Lawrence wrote:
> >>> + fi
> >>> + echo "$ret" > /dev/kmsg
> >>> +}
> >>> +
> >>> +# unload_mod(modname) - unload a kernel module
> >>> +# modname - module name to unload
> >>> +function unload_mod() {
> >>> + local mod="$1"
> >>> +
> >>> + # Wait for module reference count to clear ...
> >>> + local i=0
> >>> + while [[ $(cat /sys/module/"$mod"/refcnt) != "0" ]]; do
> >>> + i=$((i+1))
> >>> + if [[ $i -eq $MAX_RETRIES ]]; then
> >>> + die "failed to unload module $mod (refcnt)"
> >>> + fi
> >>> + sleep $RETRY_INTERVAL
> >>> + done
> >>
> >> The repeating pattern of "while <some test>; do <count>; if <count beyond
> >> max
> >> retries>; then <die>..." seems to ask for encapsulation.
> >>
> >
> > Yeah I definitely agree. I think at some point I had acquired
> > bash-fatigue; I wasn't sure how to cleanly wrap <some test> around that
> > extra logic. In C, I could do something clever with macros or a
> > callback function. My bash scripting isn't great, so I copied and
> > pasted my way through it. Suggestions welcome.
> >
>
> Okay, here's what I came up with... first off, do you prefer this kind
> of transition check vs. looking only at a specific module?
>
> # check_transition() - verify that no livepatch transition in effect
> function check_transition() {
> grep -q '^1$' /sys/kernel/livepatch/*/transition 2>/dev/null
> }
Elegant!
> then wrap the retry/timeout logic like:
>
> # retry_cmd(cmd) - loop a command until it is successful or
> # $MAX_RETRIES, sleeping $RETRY_INTERVAL in
> # between tries
> # cmd - command and its arguments to run
> function retry_cmd() {
> local cmd="$*"
> local i=0
> while eval "$cmd"; do
> i=$((i+1))
> [[ $i -eq $MAX_RETRIES ]] && return 1
> sleep $RETRY_INTERVAL
> done
> return 0
> }
>
> and the callers to something like:
>
> # wait_for_transition() - wait until all livepatch transitions clear
> function wait_for_transition() {
> retry_cmd check_transition ||
> die "failed to complete transition"
> }
My idea was to make the die() part of the retry loop. This implementation is,
however, more flexible.
> I can create similar check() functions to eval for sysfs file existence,
> file content, reference count, etc. to remove all the other
> retry/timeout loops.
I think check_*() functions can be avoided for trivial tests. retry_cmd() can
be passed a more complex command string than a single function name.
Regarding naming, I'd say wait_false() or similar would better describe what
retry_cmd() does.
Libor
--
Libor Pechacek
SUSE Labs
