RE: [PATCH v2] usb-storage: Add a limitation for blk_queue_max_hw_sectors()

[Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>]

Hi Alan,

> From: Alan Stern, Sent: Wednesday, July 3, 2019 11:20 PM
> 
> On Wed, 3 Jul 2019, Yoshihiro Shimoda wrote:
<snip>
> > IIUC, usb-storage driver should take care of calling blk_queue_ APIs anyway because:
> >
> >  - As Christoph mentioned before on the email [1], usb-storage has a special
> >    max_sectors quirk for tape and SuperSpeed devices.
> >  - Since blk_queue_* APIs don't take device structure pointer, the block layer
> >    cannot call any DMA mapping APIs. So, even if any other DMA fields are copied,
> >    the behavior is not changed.
> 
> Although the blk_queue_* APIs don't take device structure pointers, the
> SCSI layer does know about devices.  And since it is the SCSI layer
> which creates the request queue, changing the DMA fields should change
> the behavior.
> 
> However, you are correct that usb-storage has to call the blk_queue_*
> APIs anyway.  So I guess your patch is the right thing to do after all.
> 
> Acked-by: Alan Stern <stern@rowland.harvard.edu>

Thank you very much for your Acked-by!

Greg, if possible, would you merge this patch into v5.2?

Best regards,
Yoshihiro Shimoda

> I still think that copying the DMA fields would be a good idea, though.
> 
> Alan Stern
> 
> > [1]
> > https://www.spinics.net/lists/linux-usb/msg181527.html
> >
> > What do you think?
> >
> > Best regards,
> > Yoshihiro Shimoda
> >
> > > So what I would like to see is a new subroutine -- perhaps in the
> > > driver core -- that copies the DMA fields from one struct device to
> > > another.  Then we could call this subroutine in usb_alloc_dev() and
> > > usb_set_configuration() instead of copying the information manually.
> > >
> > > Greg and Christoph, does that make sense?
> > >
> > > Yoshihiro, would you like to write a patch that does this?
> > >
> > > Alan Stern