Re: [PATCH v3 00/20] sg: add v4 interface

[James Bottomley <jejb@linux.vnet.ibm.com>]

On Wed, 2019-08-07 at 13:42 +0200, Douglas Gilbert wrote:
> This patchset extends the SCSI generic (sg) driver found in
> lk 5.3 .  The sg driver has a version number which is visible
> via ioctl(SG_GET_VERSION_NUM) and is bumped from 3.5.36 to
> 4.0.03 by this patchset. The additions and changes are
> described in some detail in this long webpage:
>     http://sg.danny.cz/sg/sg_v40.html
> 
> Most new features described in the above webpage are not
> implemented in this patchset.

Since this will be an extension of something that exists both in your
sg driver and in the block bsg interface (and thus needs an
implementation there), I added both linux-block and linux-api to the cc
(the latter because you're adding to an API).

Simply extending sg to use the v4 header protocol in uapi/linux/bsg.h
is fine modulo the code being in the right form.  The problems are the
new ioctls you want to add that would need to be present there as well.
 The specific question being how we support async or non-blocking I/O
on the sg and bsg interfaces.  The standard way we add asynchronous I/O
is supposed to be via .poll on the file descriptor.  you already use
read and write in sg and bsg doesn't have a polling interface, but it
looks like we could use MSG to signal an ioctl is ready to be serviced
for both.  Would shifting to a non-blocking poll based interface for
ioctls remove the need to add these SG_IOSUBMIT/SG_IORECEIVE ioctls
since we could now do everything over blocking or non-blocking SG_IO?

James