On Tue, 30 Dec 2014, Christoph Hellwig wrote: > > The only limits usb-storage imposes on max_sectors are those needed to > > work around bugs in the devices' USB bridges. (Okay, there's also > > something for tape drive devices, but it probably doesn't belong in > > usb-storage -- it should be handled by the SCSI tape driver.) > > > > If the ATA layer needs to set a limit on max_sectors, why doesn't it > > simply go ahead and do so? > > Because the ATA layer doesn't control the device, the bridge does. > And it seems like it doesn't communicate the maximum transfer size > properly. _Is_ there any way to communicate the maximum transfer size? I'm not aware of any SCSI command for it. It isn't part of the USB mass-storage spec. usb-storage has no clear idea what sort of device lies on the other side of the USB bridge. It might be an ATA drive, it might be a flash drive, it might not be a disk at all -- usb-storage does its best not to know or care. If you think that usb-storage needs to set a maximum transfer size for disk drives, it won't be hard to write a patch. But what about all the other possible transports? Will they each have to implement the same transfer limit? If so, shouldn't the limit be set up from a more central location, such as the sd driver? Why not have sd always set max_sectors_kb to 32767 if it isn't already smaller? Would that cause any problems? Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
