On Thu, Aug 22 2013 at 4:19pm -0400,
Mike Snitzer <snitzer@xxxxxxxxxx> wrote:
> Hi Joe,
>
> Unfortunately this isn't going to work properly. Mikulas suggested a
> new "error-rq" target.
>
> I do like the idea of a single error target that is hybrid (supports
> both bio-based and request-based) but the DM core would need to be
> updated to support this.
>
> Specifically, we'd need to check if the device (and active table) is
> already bio-based or request-based and select the appropriate type. If
> it is a new device, default to selecting bio-based.
>
> There are some wrappers and other logic thoughout DM core that will need
> auditing too.
Here is a patch that should work for your needs (I tested it to work
with 'dmsetup wipe_table' on both request-based and bio-based devices):
From: Mike Snitzer <snitzer@xxxxxxxxxx>
Date: Thu, 22 Aug 2013 18:21:38 -0400
Subject: [PATCH] dm: allow error target to replace either bio-based and request-based targets
In may be useful to switch a request-based table to the "error" target.
Enhance the DM core to allow a single hybrid target to be capable of
handling either bios or requests.
Add a request-based (.map_rq) member to the error target_type and train
dm_table_set_type() to prefer the md's established type (request-based
or bio-based). If the md doesn't have an established type default to
making the hybrid target bio-based.
Cc: Joe Jin <joe.jin@xxxxxxxxxx>
Cc: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
---
drivers/md/dm-table.c | 18 +++++++++++++++++-
drivers/md/dm-target.c | 9 ++++++++-
drivers/md/dm.h | 11 +++++++++++
3 files changed, 36 insertions(+), 2 deletions(-)
Index: linux/drivers/md/dm-table.c
===================================================================
--- linux.orig/drivers/md/dm-table.c
+++ linux/drivers/md/dm-table.c
@@ -864,10 +864,26 @@ static int dm_table_set_type(struct dm_t
struct dm_target *tgt;
struct dm_dev_internal *dd;
struct list_head *devices;
+ unsigned live_md_type;
+
+ dm_lock_md_type(t->md);
+ live_md_type = dm_get_md_type(t->md);
+ dm_unlock_md_type(t->md);
for (i = 0; i < t->num_targets; i++) {
tgt = t->targets + i;
- if (dm_target_request_based(tgt))
+ if (dm_target_hybrid(tgt)) {
+ switch (live_md_type) {
+ case DM_TYPE_NONE:
+ case DM_TYPE_BIO_BASED:
+ bio_based = 1;
+ break;
+ case DM_TYPE_REQUEST_BASED:
+ request_based = 1;
+ break;
+ }
+ }
+ else if (dm_target_request_based(tgt))
request_based = 1;
else
bio_based = 1;
Index: linux/drivers/md/dm-target.c
===================================================================
--- linux.orig/drivers/md/dm-target.c
+++ linux/drivers/md/dm-target.c
@@ -131,12 +131,19 @@ static int io_err_map(struct dm_target *
return -EIO;
}
+static int io_err_map_rq(struct dm_target *ti, struct request *clone,
+ union map_info *map_context)
+{
+ return -EIO;
+}
+
static struct target_type error_target = {
.name = "error",
- .version = {1, 1, 0},
+ .version = {1, 2, 0},
.ctr = io_err_ctr,
.dtr = io_err_dtr,
.map = io_err_map,
+ .map_rq = io_err_map_rq,
};
int __init dm_target_init(void)
Index: linux/drivers/md/dm.h
===================================================================
--- linux.orig/drivers/md/dm.h
+++ linux/drivers/md/dm.h
@@ -91,10 +91,21 @@ int dm_setup_md_queue(struct mapped_devi
#define dm_target_is_valid(t) ((t)->table)
/*
+ * To check whether the target type is bio-based or not (request-based).
+ */
+#define dm_target_bio_based(t) ((t)->type->map != NULL)
+
+/*
* To check whether the target type is request-based or not (bio-based).
*/
#define dm_target_request_based(t) ((t)->type->map_rq != NULL)
+/*
+ * To check whether the target type is a hybrid (capable of being
+ * either request-based or bio-based).
+ */
+#define dm_target_hybrid(t) (dm_target_bio_based(t) && dm_target_request_based(t))
+
/*-----------------------------------------------------------------
* A registry of target types.
*---------------------------------------------------------------*/
--
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