Re: [PATCH v4 10/11] libmultipath: don't try to set hwhandler if it is retained

["Benjamin Marzinski" <bmarzins@redhat.com>]

On Thu, Jun 22, 2017 at 04:59:12PM +0200, Martin Wilck wrote:
> Setting a device handler only works if retain_attached_hw_handler
> is 'no', or if the kernel didn't auto-assign a handler. If this
> is not the case, don't even attempt to set a different handler.
> 
> This requires reading the sysfs "dh_state" path attribute.
> 
> Signed-off-by: Martin Wilck <mwilck@suse.com>

ACK

-Ben

> ---
>  libmultipath/configure.c |  8 +++++++-
>  libmultipath/propsel.c   | 35 +++++++++++++++++++++++++++++++++++
>  2 files changed, 42 insertions(+), 1 deletion(-)
> 
> diff --git a/libmultipath/configure.c b/libmultipath/configure.c
> index 74b6f52a..03874f47 100644
> --- a/libmultipath/configure.c
> +++ b/libmultipath/configure.c
> @@ -275,15 +275,21 @@ int setup_map(struct multipath *mpp, char *params, int params_size)
>  
>  	/*
>  	 * properties selectors
> +	 *
> +	 * Ordering matters for some properties:
> +	 * - features after no_path_retry and retain_hwhandler
> +	 * - hwhandler after retain_hwhandler
> +	 * No guarantee that this list is complete, check code in
> +	 * propsel.c if in doubt.
>  	 */
>  	conf = get_multipath_config();
>  	select_pgfailback(conf, mpp);
>  	select_pgpolicy(conf, mpp);
>  	select_selector(conf, mpp);
> -	select_hwhandler(conf, mpp);
>  	select_no_path_retry(conf, mpp);
>  	select_retain_hwhandler(conf, mpp);
>  	select_features(conf, mpp);
> +	select_hwhandler(conf, mpp);
>  	select_rr_weight(conf, mpp);
>  	select_minio(conf, mpp);
>  	select_mode(conf, mpp);
> diff --git a/libmultipath/propsel.c b/libmultipath/propsel.c
> index d609394e..a86207a0 100644
> --- a/libmultipath/propsel.c
> +++ b/libmultipath/propsel.c
> @@ -19,8 +19,10 @@
>  #include "discovery.h"
>  #include "dict.h"
>  #include "util.h"
> +#include "sysfs.h"
>  #include "prioritizers/alua_rtpg.h"
>  #include <inttypes.h>
> +#include <libudev.h>
>  
>  pgpolicyfn *pgpolicies[] = {
>  	NULL,
> @@ -342,9 +344,42 @@ out:
>  	return 0;
>  }
>  
> +static int get_dh_state(struct path *pp, char *value, size_t value_len)
> +{
> +	struct udev_device *ud;
> +
> +	if (pp->udev == NULL)
> +		return -1;
> +
> +	ud = udev_device_get_parent_with_subsystem_devtype(
> +		pp->udev, "scsi", "scsi_device");
> +	if (ud == NULL)
> +		return -1;
> +
> +	return sysfs_attr_get_value(ud, "dh_state", value, value_len);
> +}
> +
>  int select_hwhandler(struct config *conf, struct multipath *mp)
>  {
>  	char *origin;
> +	struct path *pp;
> +	/* dh_state is no longer than "detached" */
> +	char handler[12];
> +	char *dh_state;
> +	int i;
> +
> +	dh_state = &handler[2];
> +	if (mp->retain_hwhandler != RETAIN_HWHANDLER_OFF) {
> +		vector_foreach_slot(mp->paths, pp, i) {
> +			if (get_dh_state(pp, dh_state, sizeof(handler) - 2) > 0
> +			    && strcmp(dh_state, "detached")) {
> +				memcpy(handler, "1 ", 2);
> +				mp->hwhandler = handler;
> +				origin = "(setting: retained by kernel driver)";
> +				goto out;
> +			}
> +		}
> +	}
>  
>  	mp_set_hwe(hwhandler);
>  	mp_set_conf(hwhandler);
> -- 
> 2.13.1