Re: [PATCH] udevadm-info: Don't access sysfs 'resource<N>' files
From: BjÃrn Mork
Date: Mon Mar 18 2013 - 13:21:08 EST
Alex Williamson <alex.williamson@xxxxxxxxxx> writes:
> At least for KVM the kernel fix is the addition of the vfio driver which
> gives us a non-sysfs way to do this. If this problem was found a few
> years later and we were ready to make the switch I'd support just
> removing these resource files. In the meantime we have userspace that
> depends on this interface, so I'm open to suggestions how to fix it.
I am puzzled by a couple of things in this discussion:
1) do you seriously mean that a userspace application (any, not just
udevadm or qemu or whatever) should be able to read and write these
registers while the device is owned by a driver? How is that ever
going to work?
2) is it really so that a device can be so fundamentally screwed up by
reading some registers, that a later driver probe cannot properly
I would have thought that the solution to all this was to return -EINVAL
on any attemt to read or write these files while a driver is bound to
the device. If userspace is going to use the API, then the application
better unbind any driver first.
Or? Am I missing something here?
> If we want to blacklist this specific device, that's fine, but as others
> have pointed out it's really a class problem. Perhaps we report 1 byte
> extra for the file length where EOF-1 is an enable byte? Is there
> anything else in file ops that we could use to make it slightly more
> complicated than open(), read() to access the device? Thanks,
If there really are devices which cannot handle reading at all, and
cannot be reset to a sane state by later driver initialization, then a
blacklist could be added for those devices. This should not be a common
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