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[libvirt] [PATCH] Add new attribute writeout to <filesystem> element



This introduces new attribute writeout 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 writeout is specified, meaning when writeout=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' writeout='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     |    8 +++++++-
 docs/schemas/domaincommon.rng |    5 +++++
 src/conf/domain_conf.c        |   29 +++++++++++++++++++++++++++--
 src/conf/domain_conf.h        |   10 ++++++++++
 src/qemu/qemu_command.c       |    9 +++++++++
 5 files changed, 58 insertions(+), 3 deletions(-)

diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
index c57b7b3..803db8e 100644
--- a/docs/formatdomain.html.in
+++ b/docs/formatdomain.html.in
@@ -1303,7 +1303,7 @@
       &lt;source name='my-vm-template'/&gt;
       &lt;target dir='/'/&gt;
     &lt;/filesystem&gt;
-    &lt;filesystem type='mount' accessmode='passthrough'&gt;
+    &lt;filesystem type='mount' accessmode='passthrough' writeout='immediate'&gt;
       &lt;driver type='path'/&gt;
       &lt;source dir='/export/to/guest'/&gt;
       &lt;target dir='/import/from/host'/&gt;
@@ -1379,6 +1379,12 @@
         </dd>
         </dl>
 
+      The filesystem block has an optional attribute <code>writeout='immediate'</code>
+      to help specify whether to skip the host page cache. When writeout is specified, meaning when 
+      writeout=immediate a writeback is explicitly initiated for the dirty pages in
+      the host page cache as part of the guest file write operation. When this attribute is not
+      specified, there are no defaults, meaning explicit writeback won't be initiated.
+
       </dd>
 
       <dt><code>source</code></dt>
diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
index 27ec1da..2298994 100644
--- a/docs/schemas/domaincommon.rng
+++ b/docs/schemas/domaincommon.rng
@@ -1106,6 +1106,11 @@
           <value>squash</value>
         </choice>
         </attribute>
+        <attribute name="writeout">
+        <choice>
+          <value>immediate</value>
+        </choice>
+        </attribute>
       </optional>
     </element>
   </define>
diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index 2c91f82..80b8eab 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -256,6 +256,9 @@ VIR_ENUM_IMPL(virDomainFSAccessMode, VIR_DOMAIN_FS_ACCESSMODE_LAST,
               "mapped",
               "squash")
 
+VIR_ENUM_IMPL(virDomainFSWriteout, VIR_DOMAIN_FS_WRITEOUT_LAST,
+              "default",
+              "immediate")
 
 VIR_ENUM_IMPL(virDomainNet, VIR_DOMAIN_NET_TYPE_LAST,
               "user",
@@ -3258,6 +3261,7 @@ virDomainFSDefParseXML(xmlNodePtr node,
     char *source = NULL;
     char *target = NULL;
     char *accessmode = NULL;
+    char *writeout = NULL;
 
     if (VIR_ALLOC(def) < 0) {
         virReportOOMError();
@@ -3286,6 +3290,17 @@ virDomainFSDefParseXML(xmlNodePtr node,
         def->accessmode = VIR_DOMAIN_FS_ACCESSMODE_PASSTHROUGH;
     }
 
+    writeout = virXMLPropString(node, "writeout");
+    if (writeout) {
+        if ((def->writeout = virDomainFSWriteoutTypeFromString(writeout)) < 0) {
+            virDomainReportError(VIR_ERR_INTERNAL_ERROR,
+                                 _("unknown filesystem writeout '%s'"), writeout);
+            goto error;
+        }
+    } else {
+        def->writeout = VIR_DOMAIN_FS_WRITEOUT_DEFAULT;
+    }
+
     cur = node->children;
     while (cur != NULL) {
         if (cur->type == XML_ELEMENT_NODE) {
@@ -3348,6 +3363,7 @@ cleanup:
     VIR_FREE(target);
     VIR_FREE(source);
     VIR_FREE(accessmode);
+    VIR_FREE(writeout);
 
     return def;
 
@@ -10006,6 +10022,7 @@ virDomainFSDefFormat(virBufferPtr buf,
     const char *type = virDomainFSTypeToString(def->type);
     const char *accessmode = virDomainFSAccessModeTypeToString(def->accessmode);
     const char *fsdriver = virDomainFSDriverTypeTypeToString(def->fsdriver);
+    const char *writeout = virDomainFSWriteoutTypeToString(def->writeout);
 
     if (!type) {
         virDomainReportError(VIR_ERR_INTERNAL_ERROR,
@@ -10022,12 +10039,20 @@ virDomainFSDefFormat(virBufferPtr buf,
     if (def->fsdriver == VIR_DOMAIN_FS_DRIVER_TYPE_PATH ||
         def->fsdriver == VIR_DOMAIN_FS_DRIVER_TYPE_DEFAULT) {
         virBufferAsprintf(buf,
-                          "    <filesystem type='%s' accessmode='%s'>\n",
+                          "    <filesystem type='%s' accessmode='%s'",
                           type, accessmode);
     } else {
         virBufferAsprintf(buf,
-                          "    <filesystem type='%s'>\n", type);
+                          "    <filesystem type='%s'", type);
     }
+ 
+    /* Dont generate anything if writeout is set to default */
+    if (def->writeout) {
+        virBufferAsprintf(buf, " writeout='%s'", writeout);
+    }
+
+    /* close the filesystem element */
+    virBufferAddLit(buf,">\n");
 
     if (def->fsdriver) {
         virBufferAsprintf(buf, "      <driver type='%s'/>\n", fsdriver);
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index 3229a6f..bf4d79b 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -450,12 +450,21 @@ enum virDomainFSAccessMode {
     VIR_DOMAIN_FS_ACCESSMODE_LAST
 };
 
+/* Filesystem Writeout */
+enum virDomainFSWriteout {
+    VIR_DOMAIN_FS_WRITEOUT_DEFAULT = 0,
+    VIR_DOMAIN_FS_WRITEOUT_IMMEDIATE,
+
+    VIR_DOMAIN_FS_WRITEOUT_LAST
+};
+
 typedef struct _virDomainFSDef virDomainFSDef;
 typedef virDomainFSDef *virDomainFSDefPtr;
 struct _virDomainFSDef {
     int type;
     int fsdriver;
     int accessmode;
+    int writeout;
     char *src;
     char *dst;
     unsigned int readonly : 1;
@@ -1973,6 +1982,7 @@ VIR_ENUM_DECL(virDomainControllerModelUSB)
 VIR_ENUM_DECL(virDomainFS)
 VIR_ENUM_DECL(virDomainFSDriverType)
 VIR_ENUM_DECL(virDomainFSAccessMode)
+VIR_ENUM_DECL(virDomainFSWriteout)
 VIR_ENUM_DECL(virDomainNet)
 VIR_ENUM_DECL(virDomainNetBackend)
 VIR_ENUM_DECL(virDomainNetVirtioTxMode)
diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 1f70eb1..ccfd092 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -108,6 +108,10 @@ VIR_ENUM_IMPL(qemuDomainFSDriver, VIR_DOMAIN_FS_DRIVER_TYPE_LAST,
               "local",
               "handle");
 
+VIR_ENUM_DECL(qemuDomainFSWriteout)
+VIR_ENUM_IMPL(qemuDomainFSWriteout, VIR_DOMAIN_FS_WRITEOUT_LAST,
+              "default",
+              "immediate");
 
 static void
 uname_normalize (struct utsname *ut)
@@ -1990,6 +1994,7 @@ char *qemuBuildFSStr(virDomainFSDefPtr fs,
 {
     virBuffer opt = VIR_BUFFER_INITIALIZER;
     const char *driver = qemuDomainFSDriverTypeToString(fs->fsdriver);
+    const char *writeout = qemuDomainFSWriteoutTypeToString(fs->writeout);
 
     if (fs->type != VIR_DOMAIN_FS_TYPE_MOUNT) {
         qemuReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
@@ -2014,6 +2019,10 @@ char *qemuBuildFSStr(virDomainFSDefPtr fs,
             virBufferAddLit(&opt, ",security_model=none");
         }
     }
+
+    if (fs->writeout != VIR_DOMAIN_FS_WRITEOUT_DEFAULT) {
+        virBufferAsprintf(&opt, ",writeout=%s", writeout);
+    }
     virBufferAsprintf(&opt, ",id=%s%s", QEMU_FSDEV_HOST_PREFIX, fs->info.alias);
     virBufferAsprintf(&opt, ",path=%s", fs->src);
 


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