conf: add 'multidevs' option

Introduce new 'multidevs' option for filesystem.

  <filesystem type='mount' accessmode='mapped' multidevs='remap'>
    <source dir='/path'/>
    <target dir='mount_tag'>
  </filesystem>

This option prevents misbehaviours on guest if a qemu 9pfs export
contains multiple devices, due to the potential file ID collisions
this otherwise may cause.
Signed-off-by: NChristian Schoenebeck <qemu_oss@crudebyte.com>
Signed-off-by: NJán Tomko <jtomko@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

docs/formatdomain.html.in

@@ -3973,7 +3973,7 @@
     <source name='my-vm-template'/>
     <target dir='/'/>
   </filesystem>
-  <filesystem type='mount' accessmode='passthrough'>
+  <filesystem type='mount' accessmode='passthrough' multidevs='remap'>
     <driver type='path' wrpolicy='immediate'/>
     <source dir='/export/to/guest'/>
     <target dir='/import/from/host'/>
@@ -4098,6 +4098,44 @@
       for more details.
       </p>
 
+      <p>
+      The filesystem element has an optional attribute <code>multidevs</code>
+      which specifies how to deal with a filesystem export containing more than
+      one device, in order to avoid file ID collisions on guest when using 9pfs
+      (<span class="since">since 6.3.0, requires QEMU 4.2</span>).
+      This attribute is not available for virtiofs. The possible values are:
+      </p>
+
+        <dl>
+        <dt><code>default</code></dt>
+        <dd>
+        Use QEMU's default setting (which currently is <code>warn</code>).
+        </dd>
+        <dt><code>remap</code></dt>
+        <dd>
+        This setting allows guest to access multiple devices per export without
+        encountering misbehaviours. Inode numbers from host are automatically
+        remapped on guest to actively prevent file ID collisions if guest
+        accesses one export containing multiple devices.
+        </dd>
+        <dt><code>forbid</code></dt>
+        <dd>
+        Only allow to access one device per export by guest. Attempts to access
+        additional devices on the same export will cause the individual
+        filesystem access by guest to fail with an error and being logged (once)
+        as error on host side.
+        </dd>
+        <dt><code>warn</code></dt>
+        <dd>
+        This setting resembles the behaviour of 9pfs prior to QEMU 4.2, that is
+        no action is performed to prevent any potential file ID collisions if an
+        export contains multiple devices, with the only exception: a warning is
+        logged (once) on host side now. This setting may lead to misbehaviours
+        on guest side if more than one device is exported per export, due to the
+        potential file ID collisions this may cause on guest side in that case.
+        </dd>
+        </dl>
+
       </dd>
 
       <p>

docs/schemas/domaincommon.rng

@@ -2706,6 +2706,16 @@
             </choice>
           </attribute>
         </optional>
+        <optional>
+          <attribute name="multidevs">
+            <choice>
+              <value>default</value>
+              <value>remap</value>
+              <value>forbid</value>
+              <value>warn</value>
+            </choice>
+          </attribute>
+        </optional>
         <optional>
           <element name='readonly'>
             <empty/>

src/conf/domain_conf.c

@@ -502,6 +502,14 @@ VIR_ENUM_IMPL(virDomainFSModel,
               "virtio-non-transitional",
 );
 
+VIR_ENUM_IMPL(virDomainFSMultidevs,
+              VIR_DOMAIN_FS_MULTIDEVS_LAST,
+              "default",
+              "remap",
+              "forbid",
+              "warn",
+);
+
 VIR_ENUM_IMPL(virDomainFSCacheMode,
               VIR_DOMAIN_FS_CACHE_MODE_LAST,
               "default",
@@ -11389,6 +11397,7 @@ virDomainFSDefParseXML(virDomainXMLOptionPtr xmlopt,
     g_autofree char *usage = NULL;
     g_autofree char *units = NULL;
     g_autofree char *model = NULL;
+    g_autofree char *multidevs = NULL;
 
     ctxt->node = node;
 
@@ -11427,6 +11436,17 @@ virDomainFSDefParseXML(virDomainXMLOptionPtr xmlopt,
         }
     }
 
+    multidevs = virXMLPropString(node, "multidevs");
+    if (multidevs) {
+        if ((def->multidevs = virDomainFSMultidevsTypeFromString(multidevs)) < 0) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                           _("unknown multidevs '%s'"), multidevs);
+            goto error;
+        }
+    } else {
+        def->multidevs = VIR_DOMAIN_FS_MULTIDEVS_DEFAULT;
+    }
+
     if (virDomainParseScaledValue("./space_hard_limit[1]",
                                   NULL, ctxt, &def->space_hard_limit,
                                   1, ULLONG_MAX, false) < 0)
@@ -25385,6 +25405,7 @@ virDomainFSDefFormat(virBufferPtr buf,
     const char *accessmode = virDomainFSAccessModeTypeToString(def->accessmode);
     const char *fsdriver = virDomainFSDriverTypeToString(def->fsdriver);
     const char *wrpolicy = virDomainFSWrpolicyTypeToString(def->wrpolicy);
+    const char *multidevs = virDomainFSMultidevsTypeToString(def->multidevs);
     const char *src = def->src->path;
     g_auto(virBuffer) driverAttrBuf = VIR_BUFFER_INITIALIZER;
     g_auto(virBuffer) driverBuf = VIR_BUFFER_INIT_CHILD(buf);
@@ -25403,6 +25424,12 @@ virDomainFSDefFormat(virBufferPtr buf,
         return -1;
     }
 
+    if (!multidevs) {
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("unexpected multidevs %d"), def->multidevs);
+        return -1;
+    }
+
     virBufferAsprintf(buf,
                       "<filesystem type='%s' accessmode='%s'",
                       type, accessmode);
@@ -25410,6 +25437,8 @@ virDomainFSDefFormat(virBufferPtr buf,
         virBufferAsprintf(buf, " model='%s'",
                           virDomainFSModelTypeToString(def->model));
     }
+    if (def->multidevs)
+        virBufferAsprintf(buf, " multidevs='%s'", multidevs);
     virBufferAddLit(buf, ">\n");
 
     virBufferAdjustIndent(buf, 2);

src/conf/domain_conf.h

@@ -796,6 +796,18 @@ typedef enum {
     VIR_DOMAIN_FS_WRPOLICY_LAST
 } virDomainFSWrpolicy;
 
+/* How to handle exports containing multiple devices. */
+typedef enum {
+    VIR_DOMAIN_FS_MULTIDEVS_DEFAULT = 0, /* Use QEMU's default setting */
+    VIR_DOMAIN_FS_MULTIDEVS_REMAP, /* Remap inodes from host to guest */
+    VIR_DOMAIN_FS_MULTIDEVS_FORBID, /* Prohibit more than one device */
+    VIR_DOMAIN_FS_MULTIDEVS_WARN, /* Just log a warning if multiple devices */
+
+    VIR_DOMAIN_FS_MULTIDEVS_LAST
+} virDomainFSMultidevs;
+
+VIR_ENUM_DECL(virDomainFSMultidevs);
+
 typedef enum {
     VIR_DOMAIN_FS_MODEL_DEFAULT = 0,
     VIR_DOMAIN_FS_MODEL_VIRTIO,
@@ -820,6 +832,7 @@ struct _virDomainFSDef {
     int wrpolicy; /* enum virDomainFSWrpolicy */
     int format; /* virStorageFileFormat */
     int model; /* virDomainFSModel */
+    int multidevs; /* virDomainFSMultidevs */
     unsigned long long usage; /* in bytes */
     virStorageSourcePtr src;
     char *dst;

tests/qemuxml2argvdata/virtio-9p-multidevs.xml

+<domain type='qemu'>
+  <name>QEMUGuest1</name>
+  <uuid>c7a5fdbd-edaf-9455-926a-d65c16db1809</uuid>
+  <memory unit='KiB'>219136</memory>
+  <currentMemory unit='KiB'>219136</currentMemory>
+  <vcpu placement='static'>1</vcpu>
+  <os>
+    <type arch='x86_64' machine='pc'>hvm</type>
+    <boot dev='hd'/>
+  </os>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu-system-x86_64</emulator>
+    <controller type='usb' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
+    </controller>
+    <controller type='ide' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
+    </controller>
+    <controller type='pci' index='0' model='pci-root'/>
+    <filesystem type='mount' accessmode='mapped' multidevs='remap'>
+      <source dir='/export/fs0'/>
+      <target dir='fs0'/>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
+    </filesystem>
+    <filesystem type='mount' accessmode='mapped' multidevs='forbid'>
+      <source dir='/export/fs1'/>
+      <target dir='fs1'/>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
+    </filesystem>
+    <filesystem type='mount' accessmode='mapped' multidevs='warn'>
+      <source dir='/export/fs2'/>
+      <target dir='fs2'/>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
+    </filesystem>
+    <serial type='pty'>
+      <target type='isa-serial' port='0'>
+        <model name='isa-serial'/>
+      </target>
+    </serial>
+    <console type='pty'>
+      <target type='serial' port='0'/>
+    </console>
+    <input type='mouse' bus='ps2'/>
+    <input type='keyboard' bus='ps2'/>
+    <memballoon model='virtio'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x0c' function='0x0'/>
+    </memballoon>
+  </devices>
+</domain>

tests/qemuxml2xmloutdata/virtio-9p-multidevs.x86_64-latest.xml

+<domain type='qemu'>
+  <name>QEMUGuest1</name>
+  <uuid>c7a5fdbd-edaf-9455-926a-d65c16db1809</uuid>
+  <memory unit='KiB'>219136</memory>
+  <currentMemory unit='KiB'>219136</currentMemory>
+  <vcpu placement='static'>1</vcpu>
+  <os>
+    <type arch='x86_64' machine='pc'>hvm</type>
+    <boot dev='hd'/>
+  </os>
+  <cpu mode='custom' match='exact' check='none'>
+    <model fallback='forbid'>qemu64</model>
+  </cpu>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu-system-x86_64</emulator>
+    <controller type='usb' index='0' model='piix3-uhci'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
+    </controller>
+    <controller type='ide' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
+    </controller>
+    <controller type='pci' index='0' model='pci-root'/>
+    <filesystem type='mount' accessmode='mapped' multidevs='remap'>
+      <source dir='/export/fs0'/>
+      <target dir='fs0'/>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
+    </filesystem>
+    <filesystem type='mount' accessmode='mapped' multidevs='forbid'>
+      <source dir='/export/fs1'/>
+      <target dir='fs1'/>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
+    </filesystem>
+    <filesystem type='mount' accessmode='mapped' multidevs='warn'>
+      <source dir='/export/fs2'/>
+      <target dir='fs2'/>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
+    </filesystem>
+    <serial type='pty'>
+      <target type='isa-serial' port='0'>
+        <model name='isa-serial'/>
+      </target>
+    </serial>
+    <console type='pty'>
+      <target type='serial' port='0'/>
+    </console>
+    <input type='mouse' bus='ps2'/>
+    <input type='keyboard' bus='ps2'/>
+    <memballoon model='virtio'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x0c' function='0x0'/>
+    </memballoon>
+  </devices>
+</domain>

tests/qemuxml2xmltest.c

@@ -1485,6 +1485,8 @@ mymain(void)
     DO_TEST_CAPS_ARCH_LATEST("x86_64-default-cpu-kvm-q35-4.2", "x86_64");
     DO_TEST_CAPS_ARCH_LATEST("x86_64-default-cpu-tcg-q35-4.2", "x86_64");
 
+    DO_TEST_CAPS_LATEST("virtio-9p-multidevs");
+
     if (getenv("LIBVIRT_SKIP_CLEANUP") == NULL)
         virFileDeleteTree(fakerootdir);