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Re: [Qemu-block] [Qemu-devel] [PATCH 1/2] dma-helpers: explicitly pass a

From: John Snow
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH 1/2] dma-helpers: explicitly pass alignment into dma-helpers
Date: Tue, 11 Oct 2016 11:47:48 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0

On 10/10/2016 03:23 PM, Mark Cave-Ayland wrote:
On 10/10/16 17:34, Eric Blake wrote:

On 10/09/2016 11:43 AM, Mark Cave-Ayland wrote:
The hard-coded default alignment is BDRV_SECTOR_SIZE, however this is not
necessarily the case for all platforms. Use this as the default alignment for
all current callers.

Signed-off-by: Mark Cave-Ayland <address@hidden>

@@ -160,8 +161,8 @@ static void dma_blk_cb(void *opaque, int ret)

-    if (dbs->iov.size & ~BDRV_SECTOR_MASK) {
-        qemu_iovec_discard_back(&dbs->iov, dbs->iov.size & ~BDRV_SECTOR_MASK);
+    if (dbs->iov.size & (dbs->align - 1)) {
+        qemu_iovec_discard_back(&dbs->iov, dbs->iov.size & (dbs->align - 1));

Would it be any smarter to use osdep.h's QEMU_IS_ALIGNED(dbs->iov.size,
dbs->align) and QEMU_ALIGN_DOWN(dbs->iov.size, dbs->align)?
Semantically it is the same, but the macros make it obvious what the
bit-twiddling is doing.

Unless you think that needs a tweak,
Reviewed-by: Eric Blake <address@hidden>

I can't say I feel too strongly about it since there are plenty of other
examples of this style in the codebase, so I'm happy to go with whatever
John/Paolo are most happy with.



I can't pretend I am consistent, but when in doubt use the macro. Not worth a respin IMO, but I think this falls out of my jurisdiction :)

Acked-by: John Snow <address@hidden>

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