[PATCH 5/9] xen: sched: make implementing .alloc_pdata optional

[Dario Faggioli <dario.faggioli@citrix.com>]

The .alloc_pdata hook of the scheduler interface is
called, in schedule_cpu_switch(), unconditionally,
for all schedulers.

This forces even schedulers that do not require any
actual allocation of per-pCPU data to:
 - contain an implementation of the hook;
 - return some artificial non-NULL value to make
   such a caller happy.

This changes allows schedulers that do not need per-pCPU
allocations to avoid implementing the hook. It also
kills such artificial implementation from the ARINC653
scheduler (and, while there, it nukes .free_pdata from
there too, which is equally useless).

Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
---
Cc: George Dunlap <george.dunlap@eu.citrix.com>
Cc: Robert VanVossen <robert.vanvossen@dornerworks.com>
Cc: Josh Whitehead <josh.whitehead@dornerworks.com>
---
 xen/common/sched_arinc653.c |   31 -------------------------------
 xen/common/schedule.c       |    6 +++---
 2 files changed, 3 insertions(+), 34 deletions(-)

diff --git a/xen/common/sched_arinc653.c b/xen/common/sched_arinc653.c
index cff5da9..ef192c3 100644
--- a/xen/common/sched_arinc653.c
+++ b/xen/common/sched_arinc653.c
@@ -455,34 +455,6 @@ a653sched_free_vdata(const struct scheduler *ops, void *priv)
 }
 
 /**
- * This function allocates scheduler-specific data for a physical CPU
- *
- * We do not actually make use of any per-CPU data but the hypervisor expects
- * a non-NULL return value
- *
- * @param ops       Pointer to this instance of the scheduler structure
- *
- * @return          Pointer to the allocated data
- */
-static void *
-a653sched_alloc_pdata(const struct scheduler *ops, int cpu)
-{
-    /* return a non-NULL value to keep schedule.c happy */
-    return SCHED_PRIV(ops);
-}
-
-/**
- * This function frees scheduler-specific data for a physical CPU
- *
- * @param ops       Pointer to this instance of the scheduler structure
- */
-static void
-a653sched_free_pdata(const struct scheduler *ops, void *pcpu, int cpu)
-{
-    /* nop */
-}
-
-/**
  * This function allocates scheduler-specific data for a domain
  *
  * We do not actually make use of any per-domain data but the hypervisor
@@ -736,9 +708,6 @@ const struct scheduler sched_arinc653_def = {
     .free_vdata     = a653sched_free_vdata,
     .alloc_vdata    = a653sched_alloc_vdata,
 
-    .free_pdata     = a653sched_free_pdata,
-    .alloc_pdata    = a653sched_alloc_pdata,
-
     .free_domdata   = a653sched_free_domdata,
     .alloc_domdata  = a653sched_alloc_domdata,
 
diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index 83244d7..0e02af2 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -1493,7 +1493,7 @@ void __init scheduler_init(void)
 int schedule_cpu_switch(unsigned int cpu, struct cpupool *c)
 {
     struct vcpu *idle;
-    void *ppriv, *ppriv_old, *vpriv, *vpriv_old;
+    void *ppriv = NULL, *ppriv_old, *vpriv, *vpriv_old;
     struct scheduler *old_ops = per_cpu(scheduler, cpu);
     struct scheduler *new_ops = (c == NULL) ? &ops : c->sched;
 
@@ -1501,8 +1501,8 @@ int schedule_cpu_switch(unsigned int cpu, struct cpupool *c)
         return 0;
 
     idle = idle_vcpu[cpu];
-    ppriv = SCHED_OP(new_ops, alloc_pdata, cpu);
-    if ( ppriv == NULL )
+    if ( (new_ops->alloc_pdata != NULL) &&
+         ((ppriv = new_ops->alloc_pdata(new_ops, cpu)) == NULL) )
         return -ENOMEM;
     vpriv = SCHED_OP(new_ops, alloc_vdata, idle, idle->domain->sched_priv);
     if ( vpriv == NULL )