Add virt-install --disk 'cache' option (Ben Kochie)

Author: crobinso

AUTHORS

@@ -36,6 +36,7 @@ Patches also received from
    Andreas Schneider <anschneider-at-suse-dot-de>
    Michael Marineau <marineam-at-gentoo-dot-org>
    Tomas Hoger <thoger-at-redhat-dot-com>
+   Ben Cochie <ben-at-nerp-dot-net>
 
    ...send patches and get your name here...
 

man/en/virt-install.pod

@@ -145,6 +145,13 @@ size (in GB) to use if creating new storage
 whether to skip fully allocating newly created storage. Value is 'true' or
 'false'. Default is 'true' (do not fully allocate).
 
+=item B<cache>
+
+The cache mode to be used. The host pagecache provides cache memory.
+The cache value can be 'none', 'writethrough', or 'writeback'.
+'writethrough' provides read caching. 'writeback' provides
+read and write caching.
+
 =back
 
 See the examples section for some uses. This option deprecates C<--file>,

tests/validation.py

@@ -138,6 +138,8 @@
                                                        "vol-noexist")},
                      { 'conn' : testconn, 'volName' : ( 1234,
                                                        "vol-noexist")},
+                     { 'path' : 'valid', 'size' : 1,
+                       'driverCache' : 'invalid' },
                     ],
 
         'valid' :   [{ 'path' : '/dev/loop0' },
@@ -151,6 +153,8 @@
                      { 'conn' : testconn, 'path' : "/pool-exist/vol-noexist",
                        'size' : 1 },
                      { 'conn' : testconn, 'volInstall': volinst},
+                     { 'path' : 'nonexist', 'size' : 1,
+                       'driverCache' : 'writethrough' },
                     ]
                 },
     'shareable' : {

virt-install

@@ -80,6 +80,7 @@ def parse_disk_option(guest, path, size):
     shared = False
     sparse = True
     bus = None
+    cache = None
 
     # Strip media type
     if path.startswith("path="):
@@ -130,6 +131,8 @@ def parse_disk_option(guest, path, size):
                 sparse = False
             else:
                 fail(_("Unknown '%s' value '%s'") % (opt_type, opt_val))
+        elif opt_type == "cache":
+            cache = opt_val
         else:
             fail(_("Unknown --disk option '%s'.") % (opt,))
 
@@ -165,7 +168,7 @@ def parse_disk_option(guest, path, size):
 
     if not devtype:
         devtype = virtinst.VirtualDisk.DEVICE_DISK
-    ret = (abspath, voltuple, volinst, devtype, bus, ro, shared, size, sparse)
+    ret = (abspath, voltuple, volinst, devtype, bus, ro, shared, size, sparse, cache)
     logging.debug("parse_disk: returning %s" % str(ret))
     return ret
 
@@ -181,14 +184,15 @@ def get_disk(disk, size, sparse, guest, hvm, conn, is_file_path):
         else:
             (path, voltuple, volinst,
              device, bus, readOnly, shared,
-             size, sparse) = parse_disk_option(guest, disk, size)
+             size, sparse, cache) = parse_disk_option(guest, disk, size)
             if not sparse and volinst:
                 volinst.allocation = volinst.capacity
 
         d = virtinst.VirtualDisk(path=path, size=size, sparse=sparse,
                                  volInstall=volinst, volName=voltuple,
                                  readOnly=readOnly, shareable=shared,
-                                 device=device, bus=bus, conn=guest.conn)
+                                 device=device, bus=bus, conn=guest.conn,
+                                 driverCache=cache)
         # Default file backed PV guests to tap driver
         if d.type == virtinst.VirtualDisk.TYPE_FILE \
            and not(hvm) and virtinst.util.is_blktap_capable():

virtinst/VirtualDisk.py

@@ -86,6 +86,12 @@ class VirtualDisk(VirtualDevice):
     driver_types = [DRIVER_TAP_RAW, DRIVER_TAP_QCOW,
         DRIVER_TAP_VMDK, DRIVER_TAP_VDISK]
 
+    CACHE_MODE_NONE = "none"
+    CACHE_MODE_WRITETHROUGH = "writethrough"
+    CACHE_MODE_WRITEBACK = "writeback"
+    cache_types = [CACHE_MODE_NONE, CACHE_MODE_WRITETHROUGH,
+        CACHE_MODE_WRITEBACK]
+
     DEVICE_DISK = "disk"
     DEVICE_CDROM = "cdrom"
     DEVICE_FLOPPY = "floppy"
@@ -98,7 +104,8 @@ class VirtualDisk(VirtualDevice):
     def __init__(self, path=None, size=None, transient=False, type=None,
                  device=DEVICE_DISK, driverName=None, driverType=None,
                  readOnly=False, sparse=True, conn=None, volObject=None,
-                 volInstall=None, volName=None, bus=None, shareable=False):
+                 volInstall=None, volName=None, bus=None, shareable=False,
+                 driverCache=None):
         """
         @param path: filesystem path to the disk image.
         @type path: C{str}
@@ -131,6 +138,8 @@ def __init__(self, path=None, size=None, transient=False, type=None,
         @type bus: C{str}
         @param shareable: If disk can be shared among VMs
         @type shareable: C{bool}
+        @param driverCache: Disk cache mode (none, writethrough, writeback)
+        @type driverCache: member of cache_types
         """
 
         VirtualDevice.__init__(self, conn=conn)
@@ -145,6 +154,7 @@ def __init__(self, path=None, size=None, transient=False, type=None,
         self._vol_install = None
         self._bus = None
         self._shareable = None
+        self._driver_cache = None
 
         # XXX: No property methods for these
         self.transient = transient
@@ -162,6 +172,7 @@ def __init__(self, path=None, size=None, transient=False, type=None,
         self._set_vol_install(volInstall, validate=False)
         self._set_bus(bus, validate=False)
         self._set_shareable(shareable, validate=False)
+        self._set_driver_cache(driverCache, validate=False)
 
         if volName:
             self.__lookup_vol_name(volName)
@@ -272,6 +283,16 @@ def _set_shareable(self, val, validate=True):
         self.__validate_wrapper("_shareable", val, validate)
     shareable = property(_get_shareable, _set_shareable)
 
+    def _get_driver_cache(self):
+        return self._driver_cache
+    def _set_driver_cache(self, val, validate=True):
+        if val is not None:
+            self._check_str(val, "cache")
+            if val not in self.cache_types:
+                raise ValueError, _("Unknown cache mode '%s'" % val)
+        self.__validate_wrapper("_driver_cache", val, validate)
+    driver_cache = property(_get_driver_cache, _set_driver_cache)
+
     # Validation assistance methods
 
     # Initializes attribute if it hasn't been done, then validates args.
@@ -657,13 +678,21 @@ def get_xml_config(self, disknode=None):
 
         ret = "    <disk type='%s' device='%s'>\n" % (self.type, self.device)
 
+        dname = self.driver_name
+        if not dname and self.driver_cache:
+            self.driver_name = "qemu"
+
         if not self.driver_name is None:
             dtypexml = ""
             if not self.driver_type is None:
                 dtypexml = " type='%s'" % self.driver_type
 
-            ret += "      <driver name='%s'%s/>\n" % (self.driver_name,
-                                                      dtypexml)
+            dcachexml = ""
+            if not self.driver_cache is None:
+                dcachexml = " cache='%s'" % self.driver_cache
+
+            ret += "      <driver name='%s'%s%s/>\n" % (self.driver_name,
+                                                      dtypexml, dcachexml)
 
         if path is not None:
             ret += "      <source %s='%s'/>\n" % (typeattr, path)