[dm-devel] [PATCH 1/2] libmultipath: hwtable: new defaults for NVMe

[Benjamin Marzinski]

On Wed, Jun 01, 2022 at 10:26:27PM +0200, mwilck at suse.com wrote:
> From: Martin Wilck <mwilck at suse.com>
> 
> So far we were using the general defaults (pgpolicy = FAILOVER,
> pgfailback = -FAILBACK_MANUAL). Xosé's late patches were setting this to
> either MULTIBUS or ANA, and -FAILBACK_IMMEDIATE, respectively
> for most specific arrays. At the same time, some vendors don't like
> seeing their NVMe arrays listed specifically in the multipath-tools
> hwtable.
> 
> IMO it makes sense to change the general defaults.
> 
> detect_prio is the default, and we probe for ANA support. Thus prio
> will be "ana" for arrays that support it, and "const" otherwise.
> With "const", GROUP_BY_PRIO degenerates to MULTIBUS, and pgfailback
> won't happen anyway. This way, our defaults match most Xosé's new entries. The
> only devices for which this patch changes behavior (from FAILOVER to MULTIBUS)
> are those generic devices that aren't listed, and don't support ANA.
> 
> I considered changing the default for no_path_retry, too, but decided against
> it. The default is "fail", and users who dislike that will need to change it.
> no_path_retry is more a policy setting than a hardware property, anyway.

I agree that these new defaults are sensible, but this patch will cause
some user's arrays to change configuration when they update.  I'm not
against doing this at all, but this is one of those patches that
distributions need to take some care with, so that they can make this
change at a sensible time.

So, unless there are other objections, I'm O.k. with this patch set, I
just wanted to point this out.

-Ben

> ---
>  libmultipath/hwtable.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/libmultipath/hwtable.c b/libmultipath/hwtable.c
> index 39daadc..e0dce84 100644
> --- a/libmultipath/hwtable.c
> +++ b/libmultipath/hwtable.c
> @@ -90,7 +90,8 @@ static struct hwentry default_hw[] = {
>  		.product       = ".*",
>  		.uid_attribute = DEFAULT_NVME_UID_ATTRIBUTE,
>  		.checker_name  = NONE,
> -		.retain_hwhandler = RETAIN_HWHANDLER_OFF,
> +		.pgpolicy      = GROUP_BY_PRIO,
> +		.pgfailback    = -FAILBACK_IMMEDIATE,
>  	},
>  	/*
>  	 * Apple
> -- 
> 2.36.1