conf: Extract logic for updating 'detect_zeroes' mode

For some reason we've decided to silently translate the disk
detect_zeroes mode if it would be invalid. Extract the
logic so that it does not need to be copypasta'd across the code base.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>

src/conf/domain_conf.c

@@ -29362,3 +29362,25 @@ virDomainDiskTranslateSourcePool(virDomainDiskDefPtr def)
     virStoragePoolDefFree(pooldef);
     return ret;
 }
+
+
+/**
+ * virDomainDiskGetDetectZeroesMode:
+ * @discard: disk/image sector discard setting
+ * @detect_zeroes: disk/image zero sector detection mode
+ *
+ * As a convenience syntax, if discards are ignored and zero detection is set
+ * to 'unmap', then simply behave like zero detection is set to 'on'.  But
+ * don't change it in the XML for easier adjustments.  This behaviour is
+ * documented.
+ */
+int
+virDomainDiskGetDetectZeroesMode(virDomainDiskDiscard discard,
+                                 virDomainDiskDetectZeroes detect_zeroes)
+{
+    if (discard != VIR_DOMAIN_DISK_DISCARD_UNMAP &&
+        detect_zeroes == VIR_DOMAIN_DISK_DETECT_ZEROES_UNMAP)
+        return VIR_DOMAIN_DISK_DETECT_ZEROES_ON;
+
+    return detect_zeroes;
+}

src/conf/domain_conf.h

@@ -3528,5 +3528,8 @@ virDomainNetResolveActualType(virDomainNetDefPtr iface)
 
 int virDomainDiskTranslateSourcePool(virDomainDiskDefPtr def);
 
+int
+virDomainDiskGetDetectZeroesMode(virDomainDiskDiscard discard,
+                                 virDomainDiskDetectZeroes detect_zeroes);
 
 #endif /* __DOMAIN_CONF_H */

src/libvirt_private.syms

@@ -326,6 +326,7 @@ virDomainDiskErrorPolicyTypeToString;
 virDomainDiskFindByBusAndDst;
 virDomainDiskGeometryTransTypeFromString;
 virDomainDiskGeometryTransTypeToString;
+virDomainDiskGetDetectZeroesMode;
 virDomainDiskGetDriver;
 virDomainDiskGetFormat;
 virDomainDiskGetSource;

src/qemu/qemu_command.c

@@ -1729,6 +1729,8 @@ qemuBuildDriveStr(virDomainDiskDefPtr disk,
                   virQEMUCapsPtr qemuCaps)
 {
     virBuffer opt = VIR_BUFFER_INITIALIZER;
+    int detect_zeroes = virDomainDiskGetDetectZeroesMode(disk->discard,
+                                                         disk->detect_zeroes);
 
     if (qemuBuildDriveSourceStr(disk, qemuCaps, &opt) < 0)
         goto error;
@@ -1808,20 +1810,7 @@ qemuBuildDriveStr(virDomainDiskDefPtr disk,
                           virDomainDiskDiscardTypeToString(disk->discard));
     }
 
-    if (disk->detect_zeroes) {
-        int detect_zeroes = disk->detect_zeroes;
-
-        /*
-         * As a convenience syntax, if discards are ignored and
-         * zero detection is set to 'unmap', then simply behave
-         * like zero detection is set to 'on'.  But don't change
-         * it in the XML for easier adjustments.  This behaviour
-         * is documented.
-         */
-        if (disk->discard != VIR_DOMAIN_DISK_DISCARD_UNMAP &&
-            detect_zeroes == VIR_DOMAIN_DISK_DETECT_ZEROES_UNMAP)
-            detect_zeroes = VIR_DOMAIN_DISK_DETECT_ZEROES_ON;
-
+    if (detect_zeroes) {
         virBufferAsprintf(&opt, ",detect-zeroes=%s",
                           virDomainDiskDetectZeroesTypeToString(detect_zeroes));
     }