qemu: add support for 'multidevs' option

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: Christian Schoenebeck <qemu_oss@crudebyte.com>
Signed-off-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

src/qemu/qemu_command.c

@@ -2632,6 +2632,13 @@ qemuBuildFSStr(virDomainFSDefPtr fs)
         } else if (fs->accessmode == VIR_DOMAIN_FS_ACCESSMODE_SQUASH) {
             virBufferAddLit(&opt, ",security_model=none");
         }
+        if (fs->multidevs == VIR_DOMAIN_FS_MULTIDEVS_REMAP) {
+            virBufferAddLit(&opt, ",multidevs=remap");
+        } else if (fs->multidevs == VIR_DOMAIN_FS_MULTIDEVS_FORBID) {
+            virBufferAddLit(&opt, ",multidevs=forbid");
+        } else if (fs->multidevs == VIR_DOMAIN_FS_MULTIDEVS_WARN) {
+            virBufferAddLit(&opt, ",multidevs=warn");
+        }
     } else if (fs->fsdriver == VIR_DOMAIN_FS_DRIVER_TYPE_HANDLE) {
         /* removed since qemu 4.0.0 see v3.1.0-29-g93aee84f57 */
         virBufferAddLit(&opt, "handle");

src/qemu/qemu_validate.c

@@ -2950,6 +2950,13 @@ qemuValidateDomainDeviceDefFS(virDomainFSDefPtr fs,
                        _("only supports mount filesystem type"));
         return -1;
     }
+    if (fs->multidevs != VIR_DOMAIN_FS_MODEL_DEFAULT &&
+        !virQEMUCapsGet(qemuCaps, QEMU_CAPS_FSDEV_MULTIDEVS))
+    {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                       _("multidevs is not supported with this QEMU binary"));
+        return -1;
+    }
 
     switch ((virDomainFSDriverType) fs->fsdriver) {
     case VIR_DOMAIN_FS_DRIVER_TYPE_DEFAULT:
@@ -3002,6 +3009,11 @@ qemuValidateDomainDeviceDefFS(virDomainFSDefPtr fs,
                            _("virtiofs is not supported with this QEMU binary"));
             return -1;
         }
+        if (fs->multidevs != VIR_DOMAIN_FS_MULTIDEVS_DEFAULT) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                           _("virtiofs does not support multidevs"));
+            return -1;
+        }
         if (qemuValidateDomainDefVirtioFSSharedMemory(def) < 0)
             return -1;
         break;

tests/qemuxml2argvdata/virtio-9p-multidevs.x86_64-latest.args

@@ -0,0 +1,45 @@
+LC_ALL=C \
+PATH=/bin \
+HOME=/tmp/lib/domain--1-QEMUGuest1 \
+USER=test \
+LOGNAME=test \
+XDG_DATA_HOME=/tmp/lib/domain--1-QEMUGuest1/.local/share \
+XDG_CACHE_HOME=/tmp/lib/domain--1-QEMUGuest1/.cache \
+XDG_CONFIG_HOME=/tmp/lib/domain--1-QEMUGuest1/.config \
+QEMU_AUDIO_DRV=none \
+/usr/bin/qemu-system-x86_64 \
+-name guest=QEMUGuest1,debug-threads=on \
+-S \
+-object secret,id=masterKey0,format=raw,\
+file=/tmp/lib/domain--1-QEMUGuest1/master-key.aes \
+-machine pc,accel=tcg,usb=off,dump-guest-core=off \
+-cpu qemu64 \
+-m 214 \
+-overcommit mem-lock=off \
+-smp 1,sockets=1,cores=1,threads=1 \
+-uuid c7a5fdbd-edaf-9455-926a-d65c16db1809 \
+-display none \
+-no-user-config \
+-nodefaults \
+-chardev socket,id=charmonitor,fd=1729,server,nowait \
+-mon chardev=charmonitor,id=monitor,mode=control \
+-rtc base=utc \
+-no-shutdown \
+-no-acpi \
+-boot strict=on \
+-device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 \
+-fsdev local,security_model=mapped,multidevs=remap,id=fsdev-fs0,\
+path=/export/fs0 \
+-device virtio-9p-pci,id=fs0,fsdev=fsdev-fs0,mount_tag=fs0,bus=pci.0,addr=0x2 \
+-fsdev local,security_model=mapped,multidevs=forbid,id=fsdev-fs1,\
+path=/export/fs1 \
+-device virtio-9p-pci,id=fs1,fsdev=fsdev-fs1,mount_tag=fs1,bus=pci.0,addr=0x3 \
+-fsdev local,security_model=mapped,multidevs=warn,id=fsdev-fs2,\
+path=/export/fs2 \
+-device virtio-9p-pci,id=fs2,fsdev=fsdev-fs2,mount_tag=fs2,bus=pci.0,addr=0x4 \
+-chardev pty,id=charserial0 \
+-device isa-serial,chardev=charserial0,id=serial0 \
+-device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0xc \
+-sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,\
+resourcecontrol=deny \
+-msg timestamp=on

tests/qemuxml2argvtest.c

@@ -3124,6 +3124,8 @@ 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);