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Re: [Xen-devel] blktap2: Depend on XEN_BLKDEV_BACKEND

To: Jan Beulich <JBeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] blktap2: Depend on XEN_BLKDEV_BACKEND
From: Simon Horman <horms@xxxxxxxxxxxx>
Date: Wed, 31 Mar 2010 19:50:08 +1100
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On Wed, Mar 31, 2010 at 09:13:06AM +0100, Jan Beulich wrote:
> >>> Simon Horman <horms@xxxxxxxxxxxx> 31.03.10 08:51 >>>
> >blktap2 needs blktap_prep_foreign.
> >This dependency ensures that if XEN_BLKDEV_BACKEND is a module
> >then blktap2 is too. Otherwise the following build error will occur:
> >
> >drivers/built-in.o: In function `blktap_prep_foreign':
> >/home/horms/projects/xen/hg/linux-2.6.18-xen.hg/drivers/xen/blktap2/device.c:448:
> >undefined reference to `blkback_pagemap_read'
> >make: *** [.tmp_vmlinux1] Error 1
> >
> >Signed-off-by: Simon Horman <horms@xxxxxxxxxxxx>
> NAK: blkback_pagemap_read() & Co don't even live in blkbk.ko,
> they're in their own module, the config option for which gets auto-
> selected. Perhaps you're not using an up-to-date tree?

Sorry, I must have had an old version of the tree at some point.
But the problem I'm seeing still seems to exist in the latest tree.
The following seems to resolve it.

From: Simon Horman <horms@xxxxxxxxxxxx>

blktap2: Depend on XEN_BLKDEV_BACKEND

blktap2 needs blktap_prep_foreign.
This dependency ensures that if CONFIG_XEN_BLKBACK_PAGEMAP is a module
then blktap2 is too. Otherwise the following build error will occur:

drivers/built-in.o: In function `blktap_prep_foreign':
undefined reference to `blkback_pagemap_read'
make: *** [.tmp_vmlinux1] Error 1

Signed-off-by: Simon Horman <horms@xxxxxxxxxxxx>

Index: linux-2.6.18-xen.hg/drivers/xen/Kconfig
--- linux-2.6.18-xen.hg.orig/drivers/xen/Kconfig        2010-03-31 
15:45:07.000000000 +0900
+++ linux-2.6.18-xen.hg/drivers/xen/Kconfig     2010-03-31 15:45:12.000000000 
@@ -65,8 +65,7 @@ config XEN_BLKDEV_TAP
        tristate "Block-device tap backend driver 2"
-       depends on XEN_BACKEND
-       default XEN_BACKEND
          The block tap driver is an alternative to the block back driver 
           and allows VM block requests to be redirected to userspace through

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