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[Qemu-devel] Fixing dma-helper qiov truncation

From: Mark Cave-Ayland
Subject: [Qemu-devel] Fixing dma-helper qiov truncation
Date: Wed, 7 Sep 2016 08:31:41 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Icedove/45.2.0

Now that the 2.8 tree is open, I'd like to resurrect this earlier patch
to switch the macio controller over to the new byte-aligned DMA helpers:

The first patch in the series is a hack to work around the issue that
byte-aligned qiovs are being truncated with the existing code. git blame
shows that this code was introduced by this commit:

commit 58f423fbd5f7f435e8dc56dfa565b043d20d1e1b
Author: Kevin Wolf <address@hidden>
Date:   Wed Jul 9 19:17:30 2014 +0200

    dma-helpers: Fix too long qiov

    If the size of the scatter/gather list isn't a multiple of 512, the
    number of sectors for the block layer request is rounded down, resulting
    in a qiov that doesn't match the request length. Truncate the qiov
to the
    new length of the request.

    This fixes the IDE qtest case /x86_64/ide/bmdma/short_prdt.

    Signed-off-by: Kevin Wolf <address@hidden>
    Reviewed-by: Eric Blake <address@hidden>

Kevin/Paolo - what should be the correct behaviour here given that the
underlying APIs are now byte-aligned?



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