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Re: [dm-devel] [PATCH v2 4/5] dm mpath: add 'default_hw_handler' feature



Mike,

> -----Original Message-----
> From: Mike Snitzer [mailto:snitzer redhat com]
> Sent: Tuesday, May 08, 2012 4:56 PM
> To: dm-devel redhat com
> Cc: agk redhat com; hare suse de; Moger, Babu; sekharan us ibm com;
> Mike Snitzer
> Subject: [PATCH v2 4/5] dm mpath: add 'default_hw_handler' feature
> 
> From: Hannes Reinecke <hare suse de>
> 
> When specifying the feature 'default_hw_handler' multipath will be use
> the currently attached hardware handler instead of trying to attach the
> one specified during table load.  If no hardware handler is attached the
> specified hardware handler will be used.

I am trying to test these patches right now.  What is the expectation from
Multipath tools for this to work correctly.  Do I have to pass following 
Parameters?

hardware_handler "1 alua"  
features "1 default_hw_handler"
 
It appears to me that the first line will forcibly load the alua handler even if
the default handler is different. 

> 
> Leverages scsi_dh_attach's ability to increment the scsi_dh's reference
> count if the same scsi_dh name is provided when attaching -- currently
> attached scsi_dh name is determined with scsi_dh_attached_handler_name.
> 
> Signed-off-by: Hannes Reinecke <hare suse de>
> Signed-off-by: Mike Snitzer <snitzer redhat com>
> ---
>  drivers/md/dm-mpath.c |   27 +++++++++++++++++++++++----
>  1 files changed, 23 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
> index c351607..0fc6849 100644
> --- a/drivers/md/dm-mpath.c
> +++ b/drivers/md/dm-mpath.c
> @@ -84,6 +84,7 @@ struct multipath {
>  	unsigned queue_io:1;		/* Must we queue all I/O? */
>  	unsigned queue_if_no_path:1;	/* Queue I/O if last path fails? */
>  	unsigned saved_queue_if_no_path:1; /* Saved state during
> suspension */
> +	unsigned use_default_hw_handler:1; /* Use attached device
> handler */
> 
>  	unsigned pg_init_retries;	/* Number of times to retry pg_init
> */
>  	unsigned pg_init_count;		/* Number of times pg_init
> called */
> @@ -567,6 +568,7 @@ static struct pgpath *parse_path(struct dm_arg_set
> *as, struct path_selector *ps
>  	int r;
>  	struct pgpath *p;
>  	struct multipath *m = ti->private;
> +	struct request_queue *q = NULL;
> 
>  	/* we need at least a path arg */
>  	if (as->argc < 1) {
> @@ -585,9 +587,18 @@ static struct pgpath *parse_path(struct dm_arg_set
> *as, struct path_selector *ps
>  		goto bad;
>  	}
> 
> -	if (m->hw_handler_name) {
> -		struct request_queue *q = bdev_get_queue(p->path.dev-
> >bdev);
> +	if (m->use_default_hw_handler || m->hw_handler_name)
> +		q = bdev_get_queue(p->path.dev->bdev);
> +
> +	if (m->use_default_hw_handler) {
> +		const char *attached_handler_name =
> scsi_dh_attached_handler_name(q);
> +		if (attached_handler_name) {
> +			kfree(m->hw_handler_name);
> +			m->hw_handler_name =
> kstrdup(attached_handler_name, GFP_KERNEL);
> +		}
> +	}
> 
> +	if (m->hw_handler_name) {
>  		r = scsi_dh_attach(q, m->hw_handler_name);
>  		if (r == -EBUSY) {
>  			/*
> @@ -759,7 +770,7 @@ static int parse_features(struct dm_arg_set *as,
> struct multipath *m)
>  	const char *arg_name;
> 
>  	static struct dm_arg _args[] = {
> -		{0, 5, "invalid number of feature args"},
> +		{0, 6, "invalid number of feature args"},
>  		{1, 50, "pg_init_retries must be between 1 and 50"},
>  		{0, 60000, "pg_init_delay_msecs must be between 0 and
> 60000"},
>  	};
> @@ -780,6 +791,11 @@ static int parse_features(struct dm_arg_set *as,
> struct multipath *m)
>  			continue;
>  		}
> 
> +		if (!strcasecmp(arg_name, "default_hw_handler")) {
> +			m->use_default_hw_handler = 1;
> +			continue;
> +		}
> +
>  		if (!strcasecmp(arg_name, "pg_init_retries") &&
>  		    (argc >= 1)) {
>  			r = dm_read_arg(_args + 1, as, &m->pg_init_retries,
> &ti->error);
> @@ -1363,13 +1379,16 @@ static int multipath_status(struct dm_target *ti,
> status_type_t type,
>  	else {
>  		DMEMIT("%u ", m->queue_if_no_path +
>  			      (m->pg_init_retries > 0) * 2 +
> -			      (m->pg_init_delay_msecs !=
> DM_PG_INIT_DELAY_DEFAULT) * 2);
> +			      (m->pg_init_delay_msecs !=
> DM_PG_INIT_DELAY_DEFAULT) * 2 +
> +			      m->use_default_hw_handler);
>  		if (m->queue_if_no_path)
>  			DMEMIT("queue_if_no_path ");
>  		if (m->pg_init_retries)
>  			DMEMIT("pg_init_retries %u ", m->pg_init_retries);
>  		if (m->pg_init_delay_msecs !=
> DM_PG_INIT_DELAY_DEFAULT)
>  			DMEMIT("pg_init_delay_msecs %u ", m-
> >pg_init_delay_msecs);
> +		if (m->use_default_hw_handler)
> +			DMEMIT("default_hw_handler ");
>  	}
> 
>  	if (!m->hw_handler_name || type == STATUSTYPE_INFO)
> --
> 1.7.4.4



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