Re: [ndctl PATCH 7/7] daxctl: add systemd service and udev rule for auto-onlining

["Verma, Vishal L" <vishal.l.verma@intel.com>]

On Fri, 2021-09-17 at 11:10 -0700, Dan Williams wrote:
> On Tue, Aug 31, 2021 at 2:05 AM Vishal Verma <vishal.l.verma@intel.com> wrote:
> > 
> > Install a helper script that calls daxctl-reconfigure-device with the
> > new 'check-config' option for a given device. This is meant to be called
> > via a systemd service.
> > 
> > Install a systemd service that calls the above wrapper script with a
> > daxctl device passed in to it via the environment.
> > 
> > Install a udev rule that is triggered for every daxctl device, and
> > triggers the above oneshot systemd service.
> > 
> > Together, these three things work such that upon boot, whenever a daxctl
> > device is found, udev triggers a device-specific systemd service called,
> > for example:
> > 
> >   daxdev-reconfigure@-dev-dax0.0.service
> 
> I'm thinking the service would be called daxdev-add, because it is
> servicing KOBJ_ADD events, or is the convention to name the service
> after what it does vs what it services?

I don't know of a convention - but 'what it does' seemed more natural
for a service than 'when it's called'. It also correlates better with
usual system service names (i.e. they are named after what they do).

> 
> Also, I'm curious why would "dax0.0" be in the service name, shouldn't
> this be scanning all dax devices and internally matching based on the
> config file?

Systemd black magic? the dax0.0 doesn't come from anything I configure
- that's just how systemd's 'instantiated services' work. Each newly
added device gets it's own service tied to a unique identifier for the
device. For these, it happens to be /dev/dax0.0, which gets escaped to
-dev-dax0.0.

More reading here:
http://0pointer.de/blog/projects/instances.html

> 
> > 
> > This initiates a daxctl-reconfigure-device with a config lookup for the
> > 'dax0.0' device. If the config has an '[auto-online <unique_id>]'
> > section, it uses the information in that to set the operating mode of
> > the device.
> > 
> > If any device is in an unexpected status, 'journalctl' can be used to
> > view the reconfiguration log for that device, for example:
> > 
> >   journalctl --unit daxdev-reconfigure@-dev-dax0.0.service
> 
> There will be a log per-device, or only if there is a service per
> device? My assumption was that this service is firing off for all
> devices so you would need to filter the log by the device-name if you
> know it... or maybe I'm misunderstanding how this udev service works.

There will be both a log and a service per device - the unit file we
supply/install is essentially a template for these instantiated
services, but the actual service kicked off is <foo>@<device-
id>.service

> 
> > 
> > Update the RPM spec file to include the newly added files to the RPM
> > build.
> > 
> > Cc: QI Fuli <qi.fuli@fujitsu.com>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
> > ---
> >  configure.ac                       |  9 ++++++++-
> >  daxctl/90-daxctl-device.rules      |  1 +
> >  daxctl/Makefile.am                 | 10 ++++++++++
> >  daxctl/daxdev-auto-reconfigure.sh  |  3 +++
> >  daxctl/daxdev-reconfigure@.service |  8 ++++++++
> >  ndctl.spec.in                      |  3 +++
> >  6 files changed, 33 insertions(+), 1 deletion(-)
> >  create mode 100644 daxctl/90-daxctl-device.rules
> >  create mode 100755 daxctl/daxdev-auto-reconfigure.sh
> >  create mode 100644 daxctl/daxdev-reconfigure@.service
> > 
> > diff --git a/configure.ac b/configure.ac
> > index 9e1c6db..df6ab10 100644
> > --- a/configure.ac
> > +++ b/configure.ac
> > @@ -160,7 +160,7 @@ AC_CHECK_FUNCS([ \
> > 
> >  AC_ARG_WITH([systemd],
> >         AS_HELP_STRING([--with-systemd],
> > -               [Enable systemd functionality (monitor). @<:@default=yes@:>@]),
> > +               [Enable systemd functionality. @<:@default=yes@:>@]),
> >         [], [with_systemd=yes])
> > 
> >  if test "x$with_systemd" = "xyes"; then
> > @@ -183,6 +183,13 @@ daxctl_modprobe_data=daxctl.conf
> >  AC_SUBST([daxctl_modprobe_datadir])
> >  AC_SUBST([daxctl_modprobe_data])
> > 
> > +AC_ARG_WITH(udevrulesdir,
> > +    [AS_HELP_STRING([--with-udevrulesdir=DIR], [udev rules.d directory])],
> > +    [UDEVRULESDIR="$withval"],
> > +    [UDEVRULESDIR='${prefix}/lib/udev/rules.d']
> > +)
> > +AC_SUBST(UDEVRULESDIR)
> > +
> >  AC_ARG_WITH([keyutils],
> >             AS_HELP_STRING([--with-keyutils],
> >                         [Enable keyutils functionality (security).  @<:@default=yes@:>@]), [], [with_keyutils=yes])
> > diff --git a/daxctl/90-daxctl-device.rules b/daxctl/90-daxctl-device.rules
> > new file mode 100644
> > index 0000000..ee0670f
> > --- /dev/null
> > +++ b/daxctl/90-daxctl-device.rules
> > @@ -0,0 +1 @@
> > +ACTION=="add", SUBSYSTEM=="dax", TAG+="systemd", ENV{SYSTEMD_WANTS}="daxdev-reconfigure@$env{DEVNAME}.service"
> > diff --git a/daxctl/Makefile.am b/daxctl/Makefile.am
> > index f30c485..d53bdcf 100644
> > --- a/daxctl/Makefile.am
> > +++ b/daxctl/Makefile.am
> > @@ -28,3 +28,13 @@ daxctl_LDADD =\
> >         $(UUID_LIBS) \
> >         $(KMOD_LIBS) \
> >         $(JSON_LIBS)
> > +
> > +bin_SCRIPTS = daxdev-auto-reconfigure.sh
> > +CLEANFILES = $(bin_SCRIPTS)
> > +
> > +udevrulesdir = $(UDEVRULESDIR)
> > +udevrules_DATA = 90-daxctl-device.rules
> > +
> > +if ENABLE_SYSTEMD_UNITS
> > +systemd_unit_DATA = daxdev-reconfigure@.service
> > +endif
> > diff --git a/daxctl/daxdev-auto-reconfigure.sh b/daxctl/daxdev-auto-reconfigure.sh
> > new file mode 100755
> > index 0000000..f6da43f
> > --- /dev/null
> > +++ b/daxctl/daxdev-auto-reconfigure.sh
> > @@ -0,0 +1,3 @@
> > +#!/bin/bash
> > +
> > +daxctl reconfigure-device --check-config "${1##*/}"
> > diff --git a/daxctl/daxdev-reconfigure@.service b/daxctl/daxdev-reconfigure@.service
> > new file mode 100644
> > index 0000000..451fef1
> > --- /dev/null
> > +++ b/daxctl/daxdev-reconfigure@.service
> > @@ -0,0 +1,8 @@
> > +[Unit]
> > +Description=Automatic daxctl device reconfiguration
> > +Documentation=man:daxctl-reconfigure-device(1)
> > +
> > +[Service]
> > +Type=forking
> > +GuessMainPID=false
> > +ExecStart=/bin/sh -c "exec daxdev-auto-reconfigure.sh %I"
> 
> Why is the daxdev-auto-reconfigure.sh indirection needed? Can this not be:
> 
> ExecStart=daxctl reconfigure-device -C %I
> 
> ...if the format of %l is the issue I think it would be good for
> reconfigure-device to be tolerant of this format.