On Mon, Jun 20, 2011 at 10:46:08AM +1000, Ryan Mallon wrote: > On 20/06/11 10:42, Matthew Wilcox wrote: >> On Mon, Jun 20, 2011 at 09:02:17AM +1000, Ryan Mallon wrote: >>> There are drivers where this makes sense. For example an FPGA device >>> with a proprietary register layout on the memory bus can be done this >>> way. The FPGA can simply be mapped in user-space via /dev/mem and >>> handled there. If the device requires no access other than memory bus >>> reads and writes then writing a custom char device driver just to get an >>> mmap function seems a bit overkill. >> Calling a 30 line device driver "overkill" might in itself be overkill? >> > I mean overkill in the sense of having to write the driver at all. Why > write a 30 line driver just to re-implement some functionality of > /dev/mem? Because it pushes the tradeoff in the right direction. Somebody wants to do something weird is a little inconvenienced vs protecting the vast majority of users from some security escalation problems. Besides, if you have a real bus with discoverable regions (like PCI BARs), the bus should have sysfs entries like /sys/bus/pci/devices/0000\:06\:06.0/resource0 that can be mmaped. Then there's no need for a device driver at all, *and* the privilege escalation isn't achievable. Of course, most embedded architectures have crap discoverability. -- Matthew Wilcox Intel Open Source Technology Centre "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step." -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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