dm mpath: add retry pg init

From: Dave Wysochanski <[email protected]>

This patch allows a failed path group initialisation command to be retried.

It adds a generic MP_RETRY flag and a "pg_init_retries" feature to device-mapper multipath which limits the number of retries.

1. A hw handler sends a path initialization command to the storage and the command completes with an error code indicating the command should be retried.

2. The hardware handler calls dm_pg_init_complete() with MP_RETRY set in err_flags to ask the dm multipath core to retry.

3. If the retry limit has not been exceeded, pg_init() is retried. Otherwise fail_path() is called.

If you are using the userspace multipath-tools or device-mapper-multipath package, you can set pg_init_retries in the 'device' section of your /etc/multipath.conf file. For example:

features "2 pg_init_retries 7"

The number of PG retries attempted is reported in the 'dmsetup status' output.

---

[AGK TODO: Perform a fresh review of the state machine changes related to dm_pg_init_complete.]

 drivers/md/dm-hw-handler.h |    1 
 drivers/md/dm-mpath.c      |   81 +++++++++++++++++++++++++++++++++++++--------
 2 files changed, 68 insertions(+), 14 deletions(-)

Index: linux-2.6.23/drivers/md/dm-hw-handler.h
===================================================================
@@ -58,5 +58,6 @@ unsigned dm_scsi_err_handler(struct hw_h
 #define MP_FAIL_PATH 1
 #define MP_BYPASS_PG 2
 #define MP_ERROR_IO  4	/* Don't retry this I/O */
+#define MP_RETRY 8
 
 #endif