Add new attribute wrpolicy to <driver> element

This introduces new attribute wrpolicy with only supported
value as immediate. This will be an optional
attribute with no defaults. This helps specify whether
to skip the host page cache.

When wrpolicy is specified, meaning when wrpolicy=immediate
a writeback is explicitly initiated for the dirty pages in
the host page cache as part of the guest file write operation.

Usage:
<filesystem type='mount' accessmode='passthrough'>
  <driver type='path' wrpolicy='immediate'/>
  <source dir='/export/to/guest'/>
  <target dir='mount_tag'/>
</filesystem>

Currently this only works with type='mount' for the QEMU/KVM driver.

Signed-off-by: Deepak C Shetty <deepakcs@linux.vnet.ibm.com>

docs/formatdomain.html.in

@@ -1396,7 +1396,7 @@
       <target dir='/'/>
     </filesystem>
     <filesystem type='mount' accessmode='passthrough'>
-      <driver type='path'/>
+      <driver type='path' wrpolicy='immediate'/>
       <source dir='/export/to/guest'/>
       <target dir='/import/from/host'/>
       <readonly/>
@@ -1423,7 +1423,12 @@
         sub-element <code>driver</code>, with an
         attribute <code>type='path'</code>
         or <code>type='handle'</code> <span class="since">(since
-        0.9.7)</span>.
+        0.9.7)</span>. The driver block has an optional attribute
+        <code>wrpolicy</code> that further controls interaction with
+        the host page cache; omitting the attribute gives default behavior,
+        while the value <code>immediate</code> means that a host writeback
+        is immediately triggered for all pages touched during a guest file
+        write operation <span class="since">(since 0.9.10)</span>.
         </dd>
         <dt><code>type='template'</code></dt>
         <dd>

docs/schemas/domaincommon.rng

@@ -1162,6 +1162,11 @@
                     <value>handle</value>
                   </choice>
                 </attribute>
+                <optional>
+                  <attribute name="wrpolicy">
+                    <value>immediate</value>
+                  </attribute>
+                </optional>
                 <empty/>
               </element>
             </optional>

src/conf/domain_conf.c

@@ -266,6 +266,9 @@ VIR_ENUM_IMPL(virDomainFSAccessMode, VIR_DOMAIN_FS_ACCESSMODE_LAST,
               "mapped",
               "squash")
 
+VIR_ENUM_IMPL(virDomainFSWrpolicy, VIR_DOMAIN_FS_WRPOLICY_LAST,
+              "default",
+              "immediate")
 
 VIR_ENUM_IMPL(virDomainNet, VIR_DOMAIN_NET_TYPE_LAST,
               "user",
@@ -3460,6 +3463,7 @@ virDomainFSDefParseXML(xmlNodePtr node,
     char *source = NULL;
     char *target = NULL;
     char *accessmode = NULL;
+    char *wrpolicy = NULL;
 
     if (VIR_ALLOC(def) < 0) {
         virReportOOMError();
@@ -3509,6 +3513,7 @@ virDomainFSDefParseXML(xmlNodePtr node,
                 def->readonly = 1;
             } else if ((fsdriver == NULL) && (xmlStrEqual(cur->name, BAD_CAST "driver"))) {
                 fsdriver = virXMLPropString(cur, "type");
+                wrpolicy = virXMLPropString(cur, "wrpolicy");
             }
         }
         cur = cur->next;
@@ -3522,6 +3527,16 @@ virDomainFSDefParseXML(xmlNodePtr node,
         }
     }
 
+    if (wrpolicy) {
+        if ((def->wrpolicy = virDomainFSWrpolicyTypeFromString(wrpolicy)) <= 0) {
+            virDomainReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                                 _("unknown filesystem write policy '%s'"), wrpolicy);
+            goto error;
+        }
+    } else {
+        def->wrpolicy = VIR_DOMAIN_FS_WRPOLICY_DEFAULT;
+    }
+
     if (source == NULL) {
         virDomainReportError(VIR_ERR_NO_SOURCE,
                              target ? "%s" : NULL, target);
@@ -3548,6 +3563,7 @@ cleanup:
     VIR_FREE(target);
     VIR_FREE(source);
     VIR_FREE(accessmode);
+    VIR_FREE(wrpolicy);
 
     return def;
 
@@ -10166,6 +10182,7 @@ virDomainFSDefFormat(virBufferPtr buf,
     const char *type = virDomainFSTypeToString(def->type);
     const char *accessmode = virDomainFSAccessModeTypeToString(def->accessmode);
     const char *fsdriver = virDomainFSDriverTypeTypeToString(def->fsdriver);
+    const char *wrpolicy = virDomainFSWrpolicyTypeToString(def->wrpolicy);
 
     if (!type) {
         virDomainReportError(VIR_ERR_INTERNAL_ERROR,
@@ -10185,7 +10202,14 @@ virDomainFSDefFormat(virBufferPtr buf,
                       type, accessmode);
 
     if (def->fsdriver) {
-        virBufferAsprintf(buf, "      <driver type='%s'/>\n", fsdriver);
+        virBufferAsprintf(buf, "      <driver type='%s'", fsdriver);
+
+        /* Don't generate anything if wrpolicy is set to default */
+        if (def->wrpolicy) {
+            virBufferAsprintf(buf, " wrpolicy='%s'", wrpolicy);
+        }
+
+        virBufferAddLit(buf, "/>\n");
     }
 
     if (def->src) {

src/conf/domain_conf.h

@@ -491,12 +491,21 @@ enum virDomainFSAccessMode {
     VIR_DOMAIN_FS_ACCESSMODE_LAST
 };
 
+/* Filesystem Write policy */
+enum virDomainFSWrpolicy {
+    VIR_DOMAIN_FS_WRPOLICY_DEFAULT = 0,
+    VIR_DOMAIN_FS_WRPOLICY_IMMEDIATE,
+
+    VIR_DOMAIN_FS_WRPOLICY_LAST
+};
+
 typedef struct _virDomainFSDef virDomainFSDef;
 typedef virDomainFSDef *virDomainFSDefPtr;
 struct _virDomainFSDef {
     int type;
     int fsdriver;
     int accessmode;
+    int wrpolicy; /* enum virDomainFSWrpolicy */
     char *src;
     char *dst;
     unsigned int readonly : 1;
@@ -1985,6 +1994,7 @@ VIR_ENUM_DECL(virDomainControllerModelUSB)
 VIR_ENUM_DECL(virDomainFS)
 VIR_ENUM_DECL(virDomainFSDriverType)
 VIR_ENUM_DECL(virDomainFSAccessMode)
+VIR_ENUM_DECL(virDomainFSWrpolicy)
 VIR_ENUM_DECL(virDomainNet)
 VIR_ENUM_DECL(virDomainNetBackend)
 VIR_ENUM_DECL(virDomainNetVirtioTxMode)

src/libvirt_private.syms

@@ -316,6 +316,8 @@ virDomainDiskTypeToString;
 virDomainFSDefFree;
 virDomainFSTypeFromString;
 virDomainFSTypeToString;
+virDomainFSWrpolicyTypeFromString;
+virDomainFSWrpolicyTypeToString;
 virDomainFindByID;
 virDomainFindByName;
 virDomainFindByUUID;

src/qemu/qemu_capabilities.c

@@ -1,7 +1,7 @@
 /*
  * qemu_capabilities.c: QEMU capabilities generation
  *
- * Copyright (C) 2006-2011 Red Hat, Inc.
+ * Copyright (C) 2006-2012 Red Hat, Inc.
  * Copyright (C) 2006 Daniel P. Berrange
  *
  * This library is free software; you can redistribute it and/or
@@ -149,6 +149,7 @@ VIR_ENUM_IMPL(qemuCaps, QEMU_CAPS_LAST,
               "blk-sg-io",
               "drive-copy-on-read",
               "cpu-host",
+              "fsdev-writeout",
     );
 
 struct qemu_feature_flags {
@@ -1090,6 +1091,8 @@ qemuCapsComputeCmdFlags(const char *help,
         qemuCapsSet(flags, QEMU_CAPS_FSDEV);
         if (strstr(fsdev, "readonly"))
             qemuCapsSet(flags, QEMU_CAPS_FSDEV_READONLY);
+        if (strstr(fsdev, "writeout"))
+            qemuCapsSet(flags, QEMU_CAPS_FSDEV_WRITEOUT);
     }
     if (strstr(help, "-smbios type"))
         qemuCapsSet(flags, QEMU_CAPS_SMBIOS_TYPE);

src/qemu/qemu_capabilities.h

@@ -1,7 +1,7 @@
 /*
  * qemu_capabilities.h: QEMU capabilities generation
  *
- * Copyright (C) 2006-2011 Red Hat, Inc.
+ * Copyright (C) 2006-2012 Red Hat, Inc.
  * Copyright (C) 2006 Daniel P. Berrange
  *
  * This library is free software; you can redistribute it and/or
@@ -122,6 +122,7 @@ enum qemuCapsFlags {
     QEMU_CAPS_VIRTIO_BLK_SG_IO   = 81, /* support for SG_IO commands, reportedly added in 0.11 */
     QEMU_CAPS_DRIVE_COPY_ON_READ = 82, /* -drive copy-on-read */
     QEMU_CAPS_CPU_HOST          = 83, /* support for -cpu host */
+    QEMU_CAPS_FSDEV_WRITEOUT     = 84, /* -fsdev writeout supported */
 
     QEMU_CAPS_LAST,                   /* this must always be the last item */
 };

src/qemu/qemu_command.c

@@ -2138,6 +2138,7 @@ char *qemuBuildFSStr(virDomainFSDefPtr fs,
 {
     virBuffer opt = VIR_BUFFER_INITIALIZER;
     const char *driver = qemuDomainFSDriverTypeToString(fs->fsdriver);
+    const char *wrpolicy = virDomainFSWrpolicyTypeToString(fs->wrpolicy);
 
     if (fs->type != VIR_DOMAIN_FS_TYPE_MOUNT) {
         qemuReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
@@ -2170,6 +2171,17 @@ char *qemuBuildFSStr(virDomainFSDefPtr fs,
             goto error;
         }
     }
+
+    if (fs->wrpolicy) {
+       if (qemuCapsGet(qemuCaps, QEMU_CAPS_FSDEV_WRITEOUT)) {
+           virBufferAsprintf(&opt, ",writeout=%s", wrpolicy);
+       } else {
+           qemuReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                          _("filesystem writeout not supported"));
+           goto error;
+       }
+    }
+
     virBufferAsprintf(&opt, ",id=%s%s", QEMU_FSDEV_HOST_PREFIX, fs->info.alias);
     virBufferAsprintf(&opt, ",path=%s", fs->src);
 

tests/qemuhelptest.c

@@ -666,7 +666,8 @@ mymain(void)
             QEMU_CAPS_FSDEV_READONLY,
             QEMU_CAPS_VIRTIO_BLK_SCSI,
             QEMU_CAPS_VIRTIO_BLK_SG_IO,
-            QEMU_CAPS_CPU_HOST);
+            QEMU_CAPS_CPU_HOST,
+            QEMU_CAPS_FSDEV_WRITEOUT);
 
     return ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE;
 }

tests/qemuxml2argvdata/qemuxml2argv-fs9p.args

@@ -4,10 +4,10 @@ unix:/tmp/test-monitor,server,nowait -no-acpi -boot c -hda \
 /dev/HostVG/QEMUGuest1 -fsdev local,security_model=passthrough,id=fsdev-fs0,\
 path=/export/to/guest -device virtio-9p-pci,id=fs0,fsdev=fsdev-fs0,\
 mount_tag=/import/from/host,bus=pci.0,addr=0x3 \
--fsdev local,security_model=mapped,id=fsdev-fs1,\
+-fsdev local,security_model=mapped,writeout=immediate,id=fsdev-fs1,\
 path=/export/to/guest2 -device virtio-9p-pci,id=fs1,fsdev=fsdev-fs1,\
 mount_tag=/import/from/host2,bus=pci.0,addr=0x4 \
--fsdev handle,id=fsdev-fs2,\
+-fsdev handle,writeout=immediate,id=fsdev-fs2,\
 path=/export/to/guest3 -device virtio-9p-pci,id=fs2,fsdev=fsdev-fs2,\
 mount_tag=/import/from/host3,bus=pci.0,addr=0x5 \
 -usb -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x6

tests/qemuxml2argvdata/qemuxml2argv-fs9p.xml

@@ -25,12 +25,12 @@
       <target dir='/import/from/host'/>
     </filesystem>
     <filesystem accessmode='mapped'>
-      <driver type='path'/>
+      <driver type='path' wrpolicy='immediate'/>
       <source dir='/export/to/guest2'/>
       <target dir='/import/from/host2'/>
     </filesystem>
     <filesystem>
-      <driver type='handle'/>
+      <driver type='handle' wrpolicy='immediate'/>
       <source dir='/export/to/guest3'/>
       <target dir='/import/from/host3'/>
     </filesystem>

tests/qemuxml2argvtest.c

@@ -651,7 +651,8 @@ mymain(void)
     DO_TEST("sound-device", false,
             QEMU_CAPS_DEVICE, QEMU_CAPS_NODEFCONFIG, QEMU_CAPS_HDA_DUPLEX);
     DO_TEST("fs9p", false,
-            QEMU_CAPS_DEVICE, QEMU_CAPS_NODEFCONFIG, QEMU_CAPS_FSDEV);
+            QEMU_CAPS_DEVICE, QEMU_CAPS_NODEFCONFIG, QEMU_CAPS_FSDEV,
+            QEMU_CAPS_FSDEV_WRITEOUT);
 
     DO_TEST("hostdev-usb-address", false, NONE);
     DO_TEST("hostdev-usb-address-device", false,