Re: [PATCH v3 1/3] libxl/cpumap: Add xc_cpumap_[setcpu, clearcpu, testcpu] to complement xc_cpumap_alloc.

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Tue, Mar 24, 2015 at 05:46:04PM +0000, Ian Campbell wrote:
> On Tue, 2015-03-24 at 11:39 -0400, Konrad Rzeszutek Wilk wrote:
> 
> Please make sure you CC all of the toolstack maintainers.
> 
> > +void xc_cpumap_clearcpu(int cpu, xc_cpumap_t map)
> > +{
> > +    clear_bit(cpu, (unsigned long *)map);
> 
> Is it necessary to worry about alignment here, since xc_cpumap_t is
> actually a uint8_t*.
> 
> I'm afraid I think it probably is on ARM at least, which is rather
> tedious.
> 
> Or do we rely on all of these always being dynamically allocated (via
> xc_cpumap_alloc) and therefore "suitably aligned so that it may be
> assigned to a pointer to any type of object"[0]  following calloc ,
> avoids the issue in practice?
> 
> I think we probably do, does anyone disagree with that assessment?


We can also do and not worry about it:

>From 4620f9b35622ddf70db754f87a9114c235eb01de Mon Sep 17 00:00:00 2001
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Date: Tue, 24 Mar 2015 16:23:08 -0400
Subject: [PATCH] swap

---
 tools/libxc/xc_misc.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/tools/libxc/xc_misc.c b/tools/libxc/xc_misc.c
index 7514b84..19a1b18 100644
--- a/tools/libxc/xc_misc.c
+++ b/tools/libxc/xc_misc.c
@@ -94,19 +94,22 @@ xc_cpumap_t xc_cpumap_alloc(xc_interface *xch)
     return calloc(1, sz);
 }
 
+#define BITS_PER_CPUMAP(map) (sizeof(*map) * 8)
+#define CPUMAP_ENTRY(cpu, map) ((map))[(cpu) / BITS_PER_CPUMAP(map)]
+#define CPUMAP_SHIFT(cpu, map) ((cpu) % BITS_PER_CPUMAP(map))
 void xc_cpumap_clearcpu(int cpu, xc_cpumap_t map)
 {
-    clear_bit(cpu, (unsigned long *)map);
+    CPUMAP_ENTRY(cpu, map) &= ~(1U << CPUMAP_SHIFT(cpu, map));
 }
 
 void xc_cpumap_setcpu(int cpu, xc_cpumap_t map)
 {
-    set_bit(cpu, (unsigned long *)map);
+    CPUMAP_ENTRY(cpu, map) |= (1U << CPUMAP_SHIFT(cpu, map));
 }
 
 int xc_cpumap_testcpu(int cpu, xc_cpumap_t map)
 {
-    return test_bit(cpu, (unsigned long *)map);
+    return (CPUMAP_ENTRY(cpu, map) >> CPUMAP_SHIFT(cpu, map)) & 1;
 }
 
 xc_nodemap_t xc_nodemap_alloc(xc_interface *xch)
-- 
2.1.0