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Re: [Qemu-devel] Re: [PATCH 2 of 5] add can_dma/post_dma for direct IO

From: Avi Kivity
Subject: Re: [Qemu-devel] Re: [PATCH 2 of 5] add can_dma/post_dma for direct IO
Date: Tue, 16 Dec 2008 19:09:37 +0200
User-agent: Thunderbird (X11/20081119)

Blue Swirl wrote:
 I don't understand.  It's not a device that needs bouncing, it's a
particular transfer.  This could be either due to the transfer targeting
mmio, or due to the transfer requiring a transformation.

Should the bouncing be something more much complex, for example
negotiated between the devices? Or maybe the devices set up a
transforming and non-transforming channel (which the other end should
be able to transform some more) and use them as needed?

Yes.  We already have two cases:

- may do partial request: useful for block storage where requests can be huge - need full request: networking, where you can't send or receive half a packet; on the other hand, packets are small (even with tso)

You're adding a third case, always bounce, when the data undergoes a transformation which can't happen in-place.

error compiling committee.c: too many arguments to function

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