[PATCH v1 2/2] libxl: vcpu-set - allow to decrease vcpu count on overcommitted guests (v2)

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

We have a check to warn the user if they are overcommitting.
But the check only checks the hosts CPU amount and does
not take into account the case when the user is trying to fix
the overcommit. That is - they want to limit the amount of
online VCPUs.

This fix allows the user to offline vCPUs without any
warnings when they are running an overcommitted guest.

Also while at it, remove crud code.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
[v2: Remove crud code as spotted by Boris]
---
 tools/libxl/xl_cmdimpl.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
index 5195914..5b27bd8 100644
--- a/tools/libxl/xl_cmdimpl.c
+++ b/tools/libxl/xl_cmdimpl.c
@@ -4754,15 +4754,21 @@ static void vcpuset(uint32_t domid, const char* nr_vcpus, int check_host)
      * by the host's amount of pCPUs.
      */
     if (check_host) {
+        libxl_dominfo dominfo;
+
         unsigned int host_cpu = libxl_get_max_cpus(ctx);
-        if (max_vcpus > host_cpu) {
-            fprintf(stderr, "You are overcommmitting! You have %d physical " \
-                    " CPUs and want %d vCPUs! Aborting, use --ignore-host to " \
-                    " continue\n", host_cpu, max_vcpus);
-            return;
+
+        if (libxl_domain_info(ctx, &dominfo, domid) != 0)
+            dominfo.vcpu_online = host_cpu;
+
+        if (max_vcpus > dominfo.vcpu_online) {
+            if ((max_vcpus > host_cpu)) {
+                fprintf(stderr, "You are overcommmitting! You have %d physical" \
+                        " CPUs and want %d vCPUs! Aborting, use --ignore-host to" \
+                        " continue\n", host_cpu, max_vcpus);
+                return;
+            }
         }
-        /* NB: This also limits how many are set in the bitmap */
-        max_vcpus = (max_vcpus > host_cpu ? host_cpu : max_vcpus);
     }
     if (libxl_cpu_bitmap_alloc(ctx, &cpumap, max_vcpus)) {
         fprintf(stderr, "libxl_cpu_bitmap_alloc failed\n");
-- 
1.9.3