On 10/12/21 11:50 PM, Yanling Song wrote:

On Tue, 12 Oct 2021 09:59:30 -0700
Bart Van Assche [off-list ref] wrote:

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Why is it that SG_IO is not sufficient? This is something that should
have been explained in the patch description.

There are two cases that there are no SG devices and SG_IO cannot work.
1. To access raid controller:
a. Raid controller is a scsi host, not a scsi device, so there
is no SG device associated with it.
b. Even there is a scsi device for raid controller, SG_IO
cannot work when something wrong with IO queue and only admin queue can
work;
2. To access the physical disks behinds raid controller:
raid controller only reports VDs to OS and only VDs have SG devices. OS
has no idea about physical disks behinds raid controller and there is no
SG devices associated with physical disks.

Please take a look at the bsg_setup_queue() call in ufs_bsg_probe(). 
That call associates a BSG queue with the UFS host. That queue supports 
requests of type struct ufs_bsg_request. The Fibre Channel transport 
driver does something similar. I believe that this is a better solution 
than introducing entirely new ioctls.

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Additionally, mixing driver-internal and user space definitions in
a single header file is not OK. Definitions of data structures and
ioctls that are needed by user space software should occur in a
header file in the directory include/uapi/scsi/.

Sounds reasonable. But after checking the directory
include/uapi/scsi/, there are only several files in it. It is
expected that there should be many files if developers follow the
rule. Do you know why?

If this rule is not followed, that will be a red flag for the SCSI
maintainer and something that will probably delay upstream acceptance
of this patch.

Since there are not much examples in include/uapi/scsi/, what' your
suggestion on how to put the definitions into the folder? for example,
what's the file name? spraid_ioctrl.h?

How about include/uapi/scsi/spraid.h, since I assume that that header 
file will cover all user space interfaces for interaction with the 
spraid driver?

Thanks,

Bart.