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xen: define BIOVEC_PHYS_MERGEABLE()

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Impact: allow Xen control of bio merging

When running in Xen domain with device access, we need to make sure
the block subsystem doesn't merge requests across pages which aren't
machine physically contiguous.  To do this, we define our own
BIOVEC_PHYS_MERGEABLE.  When CONFIG_XEN isn't enabled, or we're not
running in a Xen domain, this has identical behaviour to the normal
implementation.  When running under Xen, we also make sure the
underlying machine pages are the same or adjacent.

Signed-off-by: Jeremy Fitzhardinge <[email protected]>
Signed-off-by: Konrad Rzeszutek Wilk <[email protected]>
This commit is contained in:
Jeremy Fitzhardinge 2009-02-09 12:05:46 -08:00 • committed by Konrad Rzeszutek Wilk
commit d8e0420603
3 changed files with 27 additions and 1 deletions
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2
drivers/xen/Makefile
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@ -1,4 +1,4 @@
obj-y += grant-table.o features.o events.o manage.o
obj-y += grant-table.o features.o events.o manage.o biomerge.o
obj-y += xenbus/
nostackp := $(call cc-option, -fno-stack-protector)

13
drivers/xen/biomerge.c Normal file
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@ -0,0 +1,13 @@
#include <linux/bio.h>
#include <linux/io.h>
#include <xen/page.h>
bool xen_biovec_phys_mergeable(const struct bio_vec *vec1,
const struct bio_vec *vec2)
{
unsigned long mfn1 = pfn_to_mfn(page_to_pfn(vec1->bv_page));
unsigned long mfn2 = pfn_to_mfn(page_to_pfn(vec2->bv_page));
return __BIOVEC_PHYS_MERGEABLE(vec1, vec2) &&
((mfn1 == mfn2) || ((mfn1+1) == mfn2));
}