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);
}

@@ -761,7 +772,7 @@ static int parse_features(struct dm_arg_set *as, struct multipath *m)
const char *arg_name;

static struct dm_arg _args[] = {
- {0, 6, "invalid number of feature args"},
+ {0, 7, "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"},
};
@@ -787,6 +798,11 @@ static int parse_features(struct dm_arg_set *as, struct multipath *m)
continue;
}

+ if (!strcasecmp(arg_name, "default_hw_handler")) {
+ m->features |= FEATURE_DEFAULT_HW_HANDLER;
+ continue;
+ }
+
if (!strcasecmp(arg_name, "pg_init_retries") &&
(argc >= 1)) {
r = dm_read_arg(_args + 1, as, &m->pg_init_retries, &ti->error);
@@ -1371,7 +1387,8 @@ static int multipath_status(struct dm_target *ti, status_type_t type,
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->features & FEATURE_NO_PARTITIONS));
+ (m->features & FEATURE_NO_PARTITIONS) +
+ (m->features & FEATURE_DEFAULT_HW_HANDLER));
if (m->queue_if_no_path)
DMEMIT("queue_if_no_path ");
if (m->pg_init_retries)
@@ -1380,6 +1397,8 @@ static int multipath_status(struct dm_target *ti, status_type_t type,
DMEMIT("pg_init_delay_msecs %u ", m->pg_init_delay_msecs);
if (m->features & FEATURE_NO_PARTITIONS)
DMEMIT("no_partitions ");
+ if (m->features & FEATURE_DEFAULT_HW_HANDLER)
+ DMEMIT("default_hw_handler ");
}

if (!m->hw_handler_name || type == STATUSTYPE_INFO)
--
1.6.0.2

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I concur with the idea of combining both patches.

Chandra
On Tue, 2012-05-08 at 19:30 +0200, Hannes Reinecke wrote:
> 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


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