From: Mike Snitzer A SCSI device handler might get attached to a device during the initial device scan. We do not necessarily want to override this when loading a multipath table, so this patch adds a new multipath feature argument "retain_attached_hw_handler". During SCSI device scan all loaded SCSI device handlers will be consulted for a match (via scsi_dh's provided .match). If a match is found that device handler will be attached. We need a way to have userspace multipathd's provided 'hw_handler' not override the already attached hardware handler. When specifying the new feature 'retain_attached_hw_handler' multipath will 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 still be used. 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. Depends upon commit 7e8a74b177f17d100916b6ad415450f7c9508691 ("[SCSI] scsi_dh: add scsi_dh_attached_handler_name"). Signed-off-by: Mike Snitzer Tested-by: Babu Moger Reviewed-by: Chandra Seetharaman Acked-by: Hannes Reinecke Signed-off-by: Alasdair G Kergon --- drivers/md/dm-mpath.c | 47 +++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 41 insertions(+), 6 deletions(-) Index: linux/drivers/md/dm-mpath.c =================================================================== --- linux.orig/drivers/md/dm-mpath.c +++ linux/drivers/md/dm-mpath.c @@ -85,6 +85,7 @@ 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 retain_attached_hw_handler:1; /* If there's already a hw_handler present, don't change it. */ unsigned pg_init_retries; /* Number of times to retry pg_init */ unsigned pg_init_count; /* Number of times pg_init called */ @@ -568,6 +569,8 @@ static struct pgpath *parse_path(struct int r; struct pgpath *p; struct multipath *m = ti->private; + struct request_queue *q = NULL; + const char *attached_handler_name; /* we need at least a path arg */ if (as->argc < 1) { @@ -586,13 +589,37 @@ static struct pgpath *parse_path(struct goto bad; } - if (m->hw_handler_name) { - struct request_queue *q = bdev_get_queue(p->path.dev->bdev); + if (m->retain_attached_hw_handler || m->hw_handler_name) + q = bdev_get_queue(p->path.dev->bdev); + + if (m->retain_attached_hw_handler) { + attached_handler_name = scsi_dh_attached_handler_name(q, GFP_KERNEL); + if (attached_handler_name) { + /* + * Reset hw_handler_name to match the attached handler + * and clear any hw_handler_params associated with the + * ignored handler. + * + * NB. This modifies the table line to show the actual + * handler instead of the original table passed in. + */ + kfree(m->hw_handler_name); + m->hw_handler_name = attached_handler_name; + + kfree(m->hw_handler_params); + m->hw_handler_params = NULL; + } + } + if (m->hw_handler_name) { + /* + * Increments scsi_dh reference, even when using an + * already-attached handler. + */ r = scsi_dh_attach(q, m->hw_handler_name); if (r == -EBUSY) { /* - * Already attached to different hw_handler, + * Already attached to different hw_handler: * try to reattach with correct one. */ scsi_dh_detach(q); @@ -760,7 +787,7 @@ static int parse_features(struct dm_arg_ 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"}, }; @@ -781,6 +808,11 @@ static int parse_features(struct dm_arg_ continue; } + if (!strcasecmp(arg_name, "retain_attached_hw_handler")) { + m->retain_attached_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); @@ -1364,13 +1396,16 @@ static int multipath_status(struct dm_ta 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->retain_attached_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->retain_attached_hw_handler) + DMEMIT("retain_attached_hw_handler "); } if (!m->hw_handler_name || type == STATUSTYPE_INFO) @@ -1656,7 +1691,7 @@ out: *---------------------------------------------------------------*/ static struct target_type multipath_target = { .name = "multipath", - .version = {1, 4, 0}, + .version = {1, 5, 0}, .module = THIS_MODULE, .ctr = multipath_ctr, .dtr = multipath_dtr,