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[libvirt] [RFC v4] Export KVM Host Power Management capabilities



This patch exports KVM Host Power Management capabilities as XML so that
higher-level systems management software can make use of these features
available in the host.

The script "pm-is-supported" (from pm-utils package) is run to discover if
Suspend-to-RAM (S3) or Suspend-to-Disk (S4) is supported by the host.
If either of them are supported, then a new tag "<power_management>" is
introduced in the XML under the <host> tag.

Eg: When the host supports both S3 and S4, the XML looks like this:

<capabilities>

  <host>
    <uuid>dc699581-48a2-11cb-b8a8-9a0265a79bbe</uuid>
    <cpu>
      <arch>i686</arch>
      <model>coreduo</model>
      <vendor>Intel</vendor>
      <topology sockets='1' cores='2' threads='1'/>
      <feature name='xtpr'/>
      <feature name='tm2'/>
      <feature name='est'/>
      <feature name='vmx'/>
      <feature name='pbe'/>
      <feature name='tm'/>
      <feature name='ht'/>
      <feature name='ss'/>
      <feature name='acpi'/>
      <feature name='ds'/>
    </cpu>
    <power_management>         <<<=== New host power management features
      <S3/>
      <S4/>
    </power_management>
    <migration_features>
      <live/>
      <uri_transports>
        <uri_transport>tcp</uri_transport>
      </uri_transports>
    </migration_features>
  </host>
     .
     .
     .

However in case the query to check for power management features succeeded,
but the host does not support any such feature, then the XML will contain
an empty <power_management/> tag. In the event that the PM query itself
failed, the XML will not contain any "power_management" tag.


Open issues:
-----------
1. Design new APIs in libvirt to exploit power management features
   such as S3/S4. This was discussed in [3] and [4].


Please let me know your comments and feedback.

Changelog:
---------
v1: The idea of exporting host power management capabilities through
    libvirt was discussed in [1].

v2: A working implementation was presented for review in [2].

v3: Omissions and improvements pointed out in v2 were taken care of in [5].

References:
----------
[1] Exporting KVM host power saving capabilities through libvirt
    http://thread.gmane.org/gmane.comp.emulators.libvirt/40886

[2] http://www.redhat.com/archives/libvir-list/2011-August/msg00238.html

[3] http://www.redhat.com/archives/libvir-list/2011-August/msg00248.html

[4] http://www.redhat.com/archives/libvir-list/2011-August/msg00302.html

[5] http://www.redhat.com/archives/libvir-list/2011-August/msg00282.html

Signed-off-by: Srivatsa S. Bhat <srivatsa bhat linux vnet ibm com>
---

 docs/formatcaps.html.in      |   19 +++++++---
 docs/schemas/capability.rng  |   18 +++++++++
 include/libvirt/virterror.h  |    1 +
 libvirt.spec.in              |    2 +
 src/conf/capabilities.c      |   27 +++++++++++++-
 src/conf/capabilities.h      |    4 ++
 src/libvirt_private.syms     |    1 +
 src/qemu/qemu_capabilities.c |   18 +++++++++
 src/util/util.c              |   82 ++++++++++++++++++++++++++++++++++++++++++
 src/util/util.h              |   14 +++++++
 src/util/virterror.c         |    3 ++
 11 files changed, 183 insertions(+), 6 deletions(-)

diff --git a/docs/formatcaps.html.in b/docs/formatcaps.html.in
index a4297ce..ce6f9a6 100644
--- a/docs/formatcaps.html.in
+++ b/docs/formatcaps.html.in
@@ -28,6 +28,10 @@ BIOS you will see</p>
       &lt;feature name='xtpr'/&gt;
       ...
     &lt;/cpu&gt;
+    &lt;power_management&gt;
+      &lt;S3/&gt;
+      &lt;S4/&gt;
+    &lt;power_management/&gt;
   &lt;/host&gt;</span>
 
   &lt;!-- xen-3.0-x86_64 --&gt;
@@ -61,11 +65,16 @@ BIOS you will see</p>
   ...
 &lt;/capabilities&gt;</pre>
         <p>The first block (in red) indicates the host hardware capabilities, currently
-it is limited to the CPU properties but other information may be available,
-it shows the CPU architecture, topology, model name, and additional features
-which are not included in the model but the CPU provides them. Features of the
-chip are shown within the feature block (the block is similar to what you will
-find in a Xen fully virtualized domain description).</p>
+it is limited to the CPU properties and the power management features of
+the host platform, but other information may be available, it shows the CPU architecture,
+topology, model name, and additional features which are not included in the model but the
+CPU provides them. Features of the chip are shown within the feature block (the block is
+similar to what you will find in a Xen fully virtualized domain description). Further,
+the power management features supported by the host are shown, such as Suspend-to-RAM (S3)
+and Suspend-to-Disk (S4). In case the query for power management features succeeded but the
+host does not support any such feature, then an empty &lt;power_management/&gt;
+tag will be shown. Otherwise, if the query itself failed, no such tag will
+be displayed (i.e., there will not be any power_management block or empty tag in the XML).</p>
         <p>The second block (in blue) indicates the paravirtualization support of the
 Xen support, you will see the os_type of xen to indicate a paravirtual
 kernel, then architecture information and potential features.</p>
diff --git a/docs/schemas/capability.rng b/docs/schemas/capability.rng
index 99b4a9a..8238a37 100644
--- a/docs/schemas/capability.rng
+++ b/docs/schemas/capability.rng
@@ -35,6 +35,9 @@
         </optional>
       </element>
       <optional>
+        <ref name='power_management'/>
+      </optional>
+      <optional>
         <ref name='migration'/>
       </optional>
       <optional>
@@ -105,6 +108,21 @@
     </zeroOrMore>
   </define>
 
+  <define name='power_management'>
+    <element name='power_management'>
+      <optional>
+        <element name='S3'>
+          <empty/>
+        </element>
+      </optional>
+      <optional>
+        <element name='S4'>
+          <empty/>
+        </element>
+      </optional>
+    </element>
+  </define>
+
   <define name='migration'>
     <element name='migration_features'>
       <optional>
diff --git a/include/libvirt/virterror.h b/include/libvirt/virterror.h
index 9cac437..a831c73 100644
--- a/include/libvirt/virterror.h
+++ b/include/libvirt/virterror.h
@@ -82,6 +82,7 @@ typedef enum {
     VIR_FROM_EVENT = 40,       /* Error from event loop impl */
     VIR_FROM_LIBXL = 41,	/* Error from libxenlight driver */
     VIR_FROM_LOCKING = 42,      /* Error from lock manager */
+    VIR_FROM_CAPABILITIES = 43, /* Error from capabilities */
 } virErrorDomain;
 
 
diff --git a/libvirt.spec.in b/libvirt.spec.in
index e2b7f65..3193de3 100644
--- a/libvirt.spec.in
+++ b/libvirt.spec.in
@@ -482,6 +482,8 @@ Requires: nc
 Requires: gettext
 # Needed by virt-pki-validate script.
 Requires: gnutls-utils
+# Needed for probing the power management features of the host.
+Requires: pm-utils
 %if %{with_sasl}
 Requires: cyrus-sasl
 # Not technically required, but makes 'out-of-box' config
diff --git a/src/conf/capabilities.c b/src/conf/capabilities.c
index 2f243ae..e8ab599 100644
--- a/src/conf/capabilities.c
+++ b/src/conf/capabilities.c
@@ -29,6 +29,13 @@
 #include "util.h"
 #include "uuid.h"
 #include "cpu_conf.h"
+#include "virterror_internal.h"
+
+
+#define VIR_FROM_THIS VIR_FROM_CAPABILITIES
+
+VIR_ENUM_IMPL(virHostPMCapability, VIR_HOST_PM_LAST,
+              "S3", "S4")
 
 /**
  * virCapabilitiesNew:
@@ -201,7 +208,6 @@ virCapabilitiesAddHostFeature(virCapsPtr caps,
     return 0;
 }
 
-
 /**
  * virCapabilitiesAddHostMigrateTransport:
  * @caps: capabilities to extend
@@ -686,6 +692,25 @@ virCapabilitiesFormatXML(virCapsPtr caps)
 
     virBufferAddLit(&xml, "    </cpu>\n");
 
+    if(caps->host.powerMgmt_valid) {
+        /* The PM query was successful. */
+        if(caps->host.powerMgmt) {
+            /* The host supports some PM features. */
+            unsigned int pm = caps->host.powerMgmt;
+            virBufferAddLit(&xml, "    <power_management>\n");
+            while(pm) {
+                int bit = ffs(pm) - 1;
+                virBufferAsprintf(&xml, "      <%s/>\n",
+                    virHostPMCapabilityTypeToString(bit));
+                pm &= ~(1U << bit);
+            }
+            virBufferAddLit(&xml, "    </power_management>\n");
+        } else {
+            /* The host does not support any PM feature. */
+            virBufferAddLit(&xml, "    <power_management/>\n");
+        }
+    }
+
     if (caps->host.offlineMigrate) {
         virBufferAddLit(&xml, "    <migration_features>\n");
         if (caps->host.liveMigrate)
diff --git a/src/conf/capabilities.h b/src/conf/capabilities.h
index e2fa1d6..c51f220 100644
--- a/src/conf/capabilities.h
+++ b/src/conf/capabilities.h
@@ -105,6 +105,10 @@ struct _virCapsHost {
     size_t nfeatures;
     size_t nfeatures_max;
     char **features;
+    bool powerMgmt_valid;
+    unsigned int powerMgmt;    /* Bitmask of the PM capabilities.
+                                * See enum virHostPMCapability.
+                                */
     int offlineMigrate;
     int liveMigrate;
     size_t nmigrateTrans;
diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 830222b..40fc4d0 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -1058,6 +1058,7 @@ virFormatMacAddr;
 virGenerateMacAddr;
 virGetGroupID;
 virGetHostname;
+virGetPMCapabilities;
 virGetUserDirectory;
 virGetUserID;
 virGetUserName;
diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
index 3f36212..581b80f 100644
--- a/src/qemu/qemu_capabilities.c
+++ b/src/qemu/qemu_capabilities.c
@@ -794,6 +794,8 @@ virCapsPtr qemuCapsInit(virCapsPtr old_caps)
     struct utsname utsname;
     virCapsPtr caps;
     int i;
+    int status = -1;
+    unsigned int pmbitmask = 0;
     char *xenner = NULL;
 
     /* Really, this never fails - look at the man-page. */
@@ -824,6 +826,22 @@ virCapsPtr qemuCapsInit(virCapsPtr old_caps)
         old_caps->host.cpu = NULL;
     }
 
+    /* Add the power management features of the host */
+
+    status = virGetPMCapabilities(&pmbitmask);
+    if(status < 0) {
+        caps->host.powerMgmt_valid = false;
+        VIR_WARN("Failed to get host power management capabilities");
+    } else {
+        /* The PM query succeeded. */
+        caps->host.powerMgmt_valid = true;
+
+        /* The power management features supported by the host are
+         * represented as a bitmask by 'pmbitmask'.
+         */
+        caps->host.powerMgmt = pmbitmask;
+    }
+
     virCapabilitiesAddHostMigrateTransport(caps,
                                            "tcp");
 
diff --git a/src/util/util.c b/src/util/util.c
index 03a9e1a..b1a6434 100644
--- a/src/util/util.c
+++ b/src/util/util.c
@@ -2641,3 +2641,85 @@ or other application using the libvirt API.\n\
 
     return 0;
 }
+
+/**
+ * Get the Power Management Capabilities of the host system.
+ * The script 'pm-is-supported' (from the pm-utils package) is run
+ * to find out all the power management features supported by the host,
+ * such as Suspend-to-RAM (S3) and Suspend-to-Disk (S4).
+ *
+ * @bitmask: Pointer to the bitmask that must be set appropriately to
+ *           indicate all the supported host power management features.
+ *           This will be set to zero if the host does not support any
+ *           power management feature.
+ *
+ * Return values:
+ * 0 if the query was successful.
+ * -1 on error like 'pm-is-supported' is not found.
+ */
+int
+virGetPMCapabilities(unsigned int * bitmask)
+{
+
+    char *path = NULL;
+    int status = -1;
+    int ret = -1;
+    virCommandPtr cmd;
+
+    *bitmask = 0;
+    if((path = virFindFileInPath("pm-is-supported")) == NULL) {
+        virUtilError(VIR_ERR_INTERNAL_ERROR,
+                     "%s", _("Failed to get the path of pm-is-supported"));
+        return -1;
+    }
+
+    /* Check support for Suspend-to-RAM (S3) */
+    cmd = virCommandNew(path);
+    virCommandAddArg(cmd, "--suspend");
+    if(virCommandRun(cmd, &status) < 0) {
+        virUtilError(VIR_ERR_INTERNAL_ERROR,
+                     "%s", _("Failed to run command"
+                             "'pm-is-supported --suspend'"));
+        virCommandFree(cmd);
+        ret = -1;
+        goto cleanup;
+    } else {
+        ret = 0;
+
+        /* Check return code of command == 0 for success
+         * (i.e., the PM capability is supported)
+         */
+        if(status == 0)
+            *bitmask |= 1U << VIR_HOST_PM_S3;
+
+        virCommandFree(cmd);
+    }
+
+    /* Check support for Suspend-to-Disk (S4) */
+    cmd = virCommandNew(path);
+    virCommandAddArg(cmd, "--hibernate");
+    if(virCommandRun(cmd, &status) < 0) {
+        virUtilError(VIR_ERR_INTERNAL_ERROR,
+                     "%s", _("Failed to run command"
+                             "'pm-is-supported --hibernate'"));
+
+        virCommandFree(cmd);
+        ret = -1;
+        goto cleanup;
+    } else {
+        ret = 0;
+
+        /* Check return code of command == 0 for success
+         * (i.e., the PM capability is supported)
+         */
+        if(status == 0)
+            *bitmask |= 1U << VIR_HOST_PM_S4;
+
+        virCommandFree(cmd);
+    }
+
+cleanup:
+    VIR_FREE(path);
+    return ret;
+}
+
diff --git a/src/util/util.h b/src/util/util.h
index af8b15d..24a87ff 100644
--- a/src/util/util.h
+++ b/src/util/util.h
@@ -272,4 +272,18 @@ bool virIsDevMapperDevice(const char *devname) ATTRIBUTE_NONNULL(1);
 int virEmitXMLWarning(int fd,
                       const char *name,
                       const char *cmd) ATTRIBUTE_NONNULL(2) ATTRIBUTE_NONNULL(3);
+
+/* Power Management Capabilities of the host system */
+
+enum virHostPMCapability {
+    VIR_HOST_PM_S3,  /* Suspend-to-RAM */
+    VIR_HOST_PM_S4,  /* Suspend-to-Disk */
+
+    VIR_HOST_PM_LAST
+};
+
+VIR_ENUM_DECL(virHostPMCapability)
+
+int virGetPMCapabilities(unsigned int *);
+
 #endif /* __VIR_UTIL_H__ */
diff --git a/src/util/virterror.c b/src/util/virterror.c
index 9a27feb..e07de61 100644
--- a/src/util/virterror.c
+++ b/src/util/virterror.c
@@ -172,6 +172,9 @@ static const char *virErrorDomainName(virErrorDomain domain) {
         case VIR_FROM_LOCKING:
             dom = "Locking ";
             break;
+        case VIR_FROM_CAPABILITIES:
+            dom = "Capabilities ";
+            break;
     }
     return(dom);
 }


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