Messages in this thread | | | Date | Wed, 07 Nov 2007 20:41:16 -0600 | From | Anthony Liguori <> | Subject | Re: [PATCH] virtio config_ops refactoring |
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Rusty Russell wrote: > On Thursday 08 November 2007 04:30:50 Anthony Liguori wrote: >> I would prefer that the virtio API not expose a little endian standard. >> I'm currently converting config->get() ops to ioreadXX depending on the >> size which already does the endianness conversion for me so this just >> messes things up. I think it's better to let the backend deal with >> endianness since it's trivial to handle for both the PCI backend and the >> lguest backend (lguest doesn't need to do any endianness conversion). > > -ETOOMUCHMAGIC. We should either expose all the XX interfaces (but this isn't > a high-speed interface, so let's not) or not "sometimes" convert endianness. > Getting surprises because a field happens to be packed into 4 bytes is > counter-intuitive.
Then I think it's necessary to expose the XX interfaces. Otherwise, the backend has to deal with doing all register operations at a per-byte granularity which adds a whole lot of complexity on a per-device basis (as opposed to a little complexity once in the transport layer).
You really want to be able to rely on multi-byte atomic operations too when setting values. Otherwise, you need another register to just to signal when it's okay for the device to examine any given register.
Regards,
Anthony Liguori
> Since your most trivial implementation is to do a byte at a time, I don't > think you have a good argument on that basis either. > > Cheers, > Rusty.
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