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    SubjectRe: [PATCH] virtio config_ops refactoring
    On Thursday 08 November 2007 13:41:16 Anthony Liguori wrote:
    > 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).

    Huh? Take a look at the drivers, this simply isn't true. Do you have
    evidence that it will be true later?

    Plus your code will be smaller doing a single writeb/readb loop than trying to
    do a switch statement.

    > 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.

    You already do; the status register fills this role. For example, you can't
    tell what features a guest understands until it updates the status register.

    Hope that clarifies,
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      Last update: 2007-11-08 23:27    [W:0.021 / U:1.648 seconds]
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