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[libvirt] [PATCH v4] 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>
---
v2:
- added writeout as a qemu cap
- cosmetic changes in comments
- moved to using VIR_ERR_CONFIG_UNSUPPORTED
- corrected doc

v3:
- changed attr name from writeout to wrpolicy
- moved attr to be part of driver xml element

v4:
- implemented review comments given by eric blake against v3
- added wrpolicy testcase

 docs/formatdomain.html.in                     |    9 ++++++--
 docs/schemas/domaincommon.rng                 |    5 +++++
 src/conf/domain_conf.c                        |   27 ++++++++++++++++++++++++-
 src/conf/domain_conf.h                        |   10 +++++++++
 src/libvirt_private.syms                      |    2 ++
 src/qemu/qemu_capabilities.c                  |    3 +++
 src/qemu/qemu_capabilities.h                  |    1 +
 src/qemu/qemu_command.c                       |   12 +++++++++++
 tests/qemuxml2argvdata/qemuxml2argv-fs9p.args |    4 ++--
 tests/qemuxml2argvdata/qemuxml2argv-fs9p.xml  |    4 ++--
 tests/qemuxml2argvtest.c                      |    2 +-
 11 files changed, 71 insertions(+), 8 deletions(-)

diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
index faf42df..875ac22 100644
--- a/docs/formatdomain.html.in
+++ b/docs/formatdomain.html.in
@@ -1328,7 +1328,7 @@
       &lt;target dir='/'/&gt;
     &lt;/filesystem&gt;
     &lt;filesystem type='mount' accessmode='passthrough'&gt;
-      &lt;driver type='path'/&gt;
+      &lt;driver type='path' wrpolicy='immediate'/&gt;
       &lt;source dir='/export/to/guest'/&gt;
       &lt;target dir='/import/from/host'/&gt;
       &lt;readonly/&gt;
@@ -1355,7 +1355,12 @@
         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>
diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
index 243ff93..f72f7d1 100644
--- a/docs/schemas/domaincommon.rng
+++ b/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>
diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index 6c42f36..5fa23dc 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -265,6 +265,9 @@ 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",
@@ -3459,6 +3462,7 @@ virDomainFSDefParseXML(xmlNodePtr node,
     char *source = NULL;
     char *target = NULL;
     char *accessmode = NULL;
+    char *wrpolicy = NULL;
 
     if (VIR_ALLOC(def) < 0) {
         virReportOOMError();
@@ -3508,6 +3512,7 @@ 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;
@@ -3521,6 +3526,16 @@ 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);
@@ -3547,6 +3562,7 @@ cleanup:
     VIR_FREE(target);
     VIR_FREE(source);
     VIR_FREE(accessmode);
+    VIR_FREE(wrpolicy);
 
     return def;
 
@@ -10165,6 +10181,7 @@ 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,
@@ -10184,7 +10201,15 @@ 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) {
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index 7c7e93b..ac8e768 100644
--- a/src/conf/domain_conf.h
+++ b/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;
@@ -1984,6 +1993,7 @@ 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)
diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index cfb88f8..3e1ba0c 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -313,6 +313,8 @@ virDomainDiskTypeToString;
 virDomainFSDefFree;
 virDomainFSTypeFromString;
 virDomainFSTypeToString;
+virDomainFSWrpolicyTypeFromString;
+virDomainFSWrpolicyTypeToString;
 virDomainFindByID;
 virDomainFindByName;
 virDomainFindByUUID;
diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
index 530bbb1..3069dbe 100644
--- a/src/qemu/qemu_capabilities.c
+++ b/src/qemu/qemu_capabilities.c
@@ -148,6 +148,7 @@ VIR_ENUM_IMPL(qemuCaps, QEMU_CAPS_LAST,
               "virtio-blk-pci.scsi",
               "blk-sg-io",
               "drive-copy-on-read",
+              "fsdev-writeout", 
     );
 
 struct qemu_feature_flags {
@@ -1089,6 +1090,8 @@ 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);
diff --git a/src/qemu/qemu_capabilities.h b/src/qemu/qemu_capabilities.h
index ee9d5ab..4823aae 100644
--- a/src/qemu/qemu_capabilities.h
+++ b/src/qemu/qemu_capabilities.h
@@ -121,6 +121,7 @@ enum qemuCapsFlags {
     QEMU_CAPS_VIRTIO_BLK_SCSI    = 80, /* virtio-blk-pci.scsi */
     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_FSDEV_WRITEOUT     = 83, /* -fsdev writeout supported */
 
     QEMU_CAPS_LAST,                   /* this must always be the last item */
 };
diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 98824ac..77f2896 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -2129,6 +2129,7 @@ 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",
@@ -2161,6 +2162,17 @@ 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);
 
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-fs9p.args b/tests/qemuxml2argvdata/qemuxml2argv-fs9p.args
index 8579810..f244114 100644
--- a/tests/qemuxml2argvdata/qemuxml2argv-fs9p.args
+++ b/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
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-fs9p.xml b/tests/qemuxml2argvdata/qemuxml2argv-fs9p.xml
index 07d7e8a..e31db48 100644
--- a/tests/qemuxml2argvdata/qemuxml2argv-fs9p.xml
+++ b/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>
diff --git a/tests/qemuxml2argvtest.c b/tests/qemuxml2argvtest.c
index 7beaa4b..8feda9e 100644
--- a/tests/qemuxml2argvtest.c
+++ b/tests/qemuxml2argvtest.c
@@ -631,7 +631,7 @@ 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,


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