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Old 05-08-2012, 02:46 PM
Mike Snitzer
 
Default dm-multipath: 'default_hw_handler' feature

On Tue, May 08 2012 at 10:18am -0400,
Hannes Reinecke <hare@suse.de> wrote:

> This patch introduces a 'default_hw_handler' feature for
> dm-mpath. When specifying the feature 'default_hw_handler'
> dm-multipath will be using the currently attached hardware
> handler instead of trying to re-attach with the one
> specified during table creation.
> If no hardware handler is attached the specified hardware
> handler will be used.
>
> Signed-off-by: Hannes Reinecke <hare@suse.de>
> ---
> drivers/md/dm-mpath.c | 25 ++++++++++++++++++++++---
> 1 files changed, 22 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
> index 6d3f2a8..c1ef41d 100644
> --- a/drivers/md/dm-mpath.c
> +++ b/drivers/md/dm-mpath.c
> @@ -57,6 +57,7 @@ struct priority_group {
> };
>
> #define FEATURE_NO_PARTITIONS 1
> +#define FEATURE_DEFAULT_HW_HANDLER 2
>
> /* Multipath context */
> struct multipath {
> @@ -589,14 +590,24 @@ static struct pgpath *parse_path(struct dm_arg_set *as, struct path_selector *ps
>
> if (m->hw_handler_name) {
> struct request_queue *q = bdev_get_queue(p->path.dev->bdev);
> + const char *hw_handler_name = m->hw_handler_name;
>
> - r = scsi_dh_attach(q, m->hw_handler_name);
> + if (m->features & FEATURE_DEFAULT_HW_HANDLER)
> + hw_handler_name = NULL;
> +
> + r = scsi_dh_attach(q, hw_handler_name);
> if (r == -EBUSY) {
> /*
> * Already attached to different hw_handler,
> * try to reattach with correct one.
> */
> scsi_dh_detach(q);
> + r = scsi_dh_attach(q, hw_handler_name);
> + } else if (r == -EINVAL) {
> + /*
> + * No hardware handler attached, use
> + * the specified one.
> + */
> r = scsi_dh_attach(q, m->hw_handler_name);
> }

I like what you've done with the 'default_hw_handler' feature. But
you're not establishing m->hw_handler_name. As such the rest of the
dm-mpath.c code that keys off of m->hw_handler_name (e.g. reinstate_path,
pg_init_done, free_pgpaths) will not work.

Would you be OK with a hybrid of both our approaches? Use your
'default_hw_handler' feature and, rather than pass a NULL name to
scsi_dh_attach, use scsi_dh_attached_handler_name like I provided?

(I don't see a problem with altering m->hw_handler_name to reflect the
scsi_dh that is used by the path.. Babu agreed with this too).

I'd be happy to merge our dm-mpath patches and attribute authorship to
you.

Mike

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Old 05-08-2012, 05:30 PM
Hannes Reinecke
 
Default dm-multipath: 'default_hw_handler' feature

On 05/08/2012 04:46 PM, Mike Snitzer wrote:

On Tue, May 08 2012 at 10:18am -0400,
Hannes Reinecke<hare@suse.de> wrote:


This patch introduces a 'default_hw_handler' feature for
dm-mpath. When specifying the feature 'default_hw_handler'
dm-multipath will be using the currently attached hardware
handler instead of trying to re-attach with the one
specified during table creation.
If no hardware handler is attached the specified hardware
handler will be used.

Signed-off-by: Hannes Reinecke<hare@suse.de>
---
drivers/md/dm-mpath.c | 25 ++++++++++++++++++++++---
1 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 6d3f2a8..c1ef41d 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -57,6 +57,7 @@ struct priority_group {
};

#define FEATURE_NO_PARTITIONS 1
+#define FEATURE_DEFAULT_HW_HANDLER 2

/* Multipath context */
struct multipath {
@@ -589,14 +590,24 @@ static struct pgpath *parse_path(struct dm_arg_set *as, struct path_selector *ps

if (m->hw_handler_name) {
struct request_queue *q = bdev_get_queue(p->path.dev->bdev);
+ const char *hw_handler_name = m->hw_handler_name;

- r = scsi_dh_attach(q, m->hw_handler_name);
+ if (m->features& FEATURE_DEFAULT_HW_HANDLER)
+ hw_handler_name = NULL;
+
+ r = scsi_dh_attach(q, hw_handler_name);
if (r == -EBUSY) {
/*
* Already attached to different hw_handler,
* try to reattach with correct one.
*/
scsi_dh_detach(q);
+ r = scsi_dh_attach(q, hw_handler_name);
+ } else if (r == -EINVAL) {
+ /*
+ * No hardware handler attached, use
+ * the specified one.
+ */
r = scsi_dh_attach(q, m->hw_handler_name);
}


I like what you've done with the 'default_hw_handler' feature. But
you're not establishing m->hw_handler_name. As such the rest of the
dm-mpath.c code that keys off of m->hw_handler_name (e.g. reinstate_path,
pg_init_done, free_pgpaths) will not work.


Ah. True.


Would you be OK with a hybrid of both our approaches? Use your
'default_hw_handler' feature and, rather than pass a NULL name to
scsi_dh_attach, use scsi_dh_attached_handler_name like I provided?


Yes, sure. That sounds like the best approach here.

I'm not _that_ keen on my 'NULL' hw handler name approach, so your idea
of having a function for that looks like a better idea.


(I don't see a problem with altering m->hw_handler_name to reflect the
scsi_dh that is used by the path.. Babu agreed with this too).


Yep.


I'd be happy to merge our dm-mpath patches and attribute authorship to
you.


Oh, cool.
Please do.

Cheers,

Hannes
--
Dr. Hannes Reinecke zSeries & Storage
hare@suse.de +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Markus Rex, HRB 16746 (AG Nürnberg)

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Old 05-08-2012, 05:56 PM
"Moger, Babu"
 
Default dm-multipath: 'default_hw_handler' feature

> -----Original Message-----
> From: Hannes Reinecke [mailto:hare@suse.de]
> Sent: Tuesday, May 08, 2012 12:30 PM
> To: Mike Snitzer
> Cc: dm-devel@redhat.com; Moger, Babu
> Subject: Re: [PATCH 3/3] dm-multipath: 'default_hw_handler' feature
>
> On 05/08/2012 04:46 PM, Mike Snitzer wrote:
> > On Tue, May 08 2012 at 10:18am -0400,
> > Hannes Reinecke<hare@suse.de> wrote:
> >
> >> This patch introduces a 'default_hw_handler' feature for
> >> dm-mpath. When specifying the feature 'default_hw_handler'
> >> dm-multipath will be using the currently attached hardware
> >> handler instead of trying to re-attach with the one
> >> specified during table creation.
> >> If no hardware handler is attached the specified hardware
> >> handler will be used.
> >>
> >> Signed-off-by: Hannes Reinecke<hare@suse.de>
> >> ---
> >> drivers/md/dm-mpath.c | 25 ++++++++++++++++++++++---
> >> 1 files changed, 22 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
> >> index 6d3f2a8..c1ef41d 100644
> >> --- a/drivers/md/dm-mpath.c
> >> +++ b/drivers/md/dm-mpath.c
> >> @@ -57,6 +57,7 @@ struct priority_group {
> >> };
> >>
> >> #define FEATURE_NO_PARTITIONS 1
> >> +#define FEATURE_DEFAULT_HW_HANDLER 2
> >>
> >> /* Multipath context */
> >> struct multipath {
> >> @@ -589,14 +590,24 @@ static struct pgpath *parse_path(struct
> dm_arg_set *as, struct path_selector *ps
> >>
> >> if (m->hw_handler_name) {
> >> struct request_queue *q = bdev_get_queue(p->path.dev-
> >bdev);
> >> + const char *hw_handler_name = m->hw_handler_name;
> >>
> >> - r = scsi_dh_attach(q, m->hw_handler_name);
> >> + if (m->features& FEATURE_DEFAULT_HW_HANDLER)
> >> + hw_handler_name = NULL;
> >> +
> >> + r = scsi_dh_attach(q, hw_handler_name);
> >> if (r == -EBUSY) {
> >> /*
> >> * Already attached to different hw_handler,
> >> * try to reattach with correct one.
> >> */
> >> scsi_dh_detach(q);
> >> + r = scsi_dh_attach(q, hw_handler_name);
> >> + } else if (r == -EINVAL) {
> >> + /*
> >> + * No hardware handler attached, use
> >> + * the specified one.
> >> + */
> >> r = scsi_dh_attach(q, m->hw_handler_name);
> >> }
> >
> > I like what you've done with the 'default_hw_handler' feature. But
> > you're not establishing m->hw_handler_name. As such the rest of the
> > dm-mpath.c code that keys off of m->hw_handler_name (e.g.
> reinstate_path,
> > pg_init_done, free_pgpaths) will not work.
> >
> Ah. True.
>
> > Would you be OK with a hybrid of both our approaches? Use your
> > 'default_hw_handler' feature and, rather than pass a NULL name to
> > scsi_dh_attach, use scsi_dh_attached_handler_name like I provided?
> >
> Yes, sure. That sounds like the best approach here.
>
> I'm not _that_ keen on my 'NULL' hw handler name approach, so your idea
> of having a function for that looks like a better idea.
>
> > (I don't see a problem with altering m->hw_handler_name to reflect the
> > scsi_dh that is used by the path.. Babu agreed with this too).
> >
> Yep.
>
> > I'd be happy to merge our dm-mpath patches and attribute authorship to
> > you.
> >
> Oh, cool.
> Please do.

I am little bit lost with all the patches. From what I understand so far.
Multipath tools will pass following parameters..

hardware_handler "1 alua"
features "1 default_hw_handler"

On seeing the "features", dm will try to detect default handler and will initialize
m-> hw_handler_name. If the feature is not specified then old behavior should
take effect. Or if the dm cannot determine the default handler then also old behavior
should take effect.
If the dm CAN find default handler then parse_hw_handler will skip all the processing.
Is that the summary. Or Did I miss something here.




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