Re: [PATCH 10/23] zfcp: drop duplicate fsf_command from zfcp_fsf_req which is also in QTCB header

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On 11/8/18 3:44 PM, Steffen Maier wrote:
Status read buffers (SRBs, unsolicited notifications) never use a QTCB
[zfcp_fsf_req_create()]. zfcp_fsf_req_send() already uses this to
distinguish SRBs from other FSF request types. We can re-use this method
in zfcp_fsf_req_complete(). Introduce a helper function to make the check
for req->qtcb less magic.

SRBs always are FSF_QTCB_UNSOLICITED_STATUS, so we can hard-code this for
the two trace functions dealing with SRBs.

All other FSF request types have a QTCB and we can get the fsf_command
from there.

zfcp_dbf_hba_fsf_response() and thus zfcp_dbf_hba_fsf_res() are only called
for non-SRB requests so it's safe to dereference the QTCB
[zfcp_fsf_req_complete() returns early on SRB,  else calls
  zfcp_fsf_protstatus_eval() which calls zfcp_dbf_hba_fsf_response()].
In zfcp_scsi_forget_cmnd() we guard the QTCB dereference with a preceding
NULL check and rely on boolean shortcut evaluation.

As a side effect, this causes an alignment hole which we can close in
a later patch after having cleaned up all fields of struct zfcp_fsf_req.
Before:
$ pahole -C zfcp_fsf_req drivers/s390/scsi/zfcp.ko
...
	u32                        status;               /*   136     4 */
	u32                        fsf_command;          /*   140     4 */
	struct fsf_qtcb *          qtcb;                 /*   144     8 */
...
After:
$ pahole -C zfcp_fsf_req drivers/s390/scsi/zfcp.ko
...
	u32                        status;               /*   136     4 */
	/* XXX 4 bytes hole, try to pack */
	struct fsf_qtcb *          qtcb;                 /*   144     8 */
...

Signed-off-by: Steffen Maier <maier@xxxxxxxxxxxxx>
Reviewed-by: Benjamin Block <bblock@xxxxxxxxxxxxx>
---
  drivers/s390/scsi/zfcp_dbf.c  |  8 ++++----
  drivers/s390/scsi/zfcp_dbf.h  |  4 ++--
  drivers/s390/scsi/zfcp_def.h  |  7 +++++--
  drivers/s390/scsi/zfcp_fsf.c  | 14 ++++++--------
  drivers/s390/scsi/zfcp_scsi.c |  4 +++-
  5 files changed, 20 insertions(+), 17 deletions(-)

Reviewed-by: Hannes Reinecke <hare@xxxxxxxx>

Cheers,

Hannes
--
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@xxxxxxx			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)



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