qemu: domain: Add helper for translating disk cachemode to qemu flags

Add helper which will map values of disk cache mode to the flags which
are accepted by various parts of the qemu block layer.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>

src/qemu/qemu_domain.c

@@ -11866,6 +11866,81 @@ qemuDomainPrepareDiskSource(virDomainDiskDefPtr disk,
 }
 
 
+/**
+ * qemuDomainDiskCachemodeFlags:
+ *
+ * Converts disk cachemode to the cache mode options for qemu. Returns -1 for
+ * invalid @cachemode values and fills the flags and returns 0 on success.
+ * Flags may be NULL.
+ */
+int
+qemuDomainDiskCachemodeFlags(int cachemode,
+                             bool *writeback,
+                             bool *direct,
+                             bool *noflush)
+{
+    bool dummy;
+
+    if (!writeback)
+        writeback = &dummy;
+
+    if (!direct)
+        direct = &dummy;
+
+    if (!noflush)
+        noflush = &dummy;
+
+    /* Mapping of cache modes to the attributes according to qemu-options.hx
+     *              │ cache.writeback   cache.direct   cache.no-flush
+     * ─────────────┼─────────────────────────────────────────────────
+     * writeback    │ true              false          false
+     * none         │ true              true           false
+     * writethrough │ false             false          false
+     * directsync   │ false             true           false
+     * unsafe       │ true              false          true
+     */
+    switch ((virDomainDiskCache) cachemode) {
+    case VIR_DOMAIN_DISK_CACHE_DISABLE: /* 'none' */
+        *writeback = true;
+        *direct = true;
+        *noflush = false;
+        break;
+
+    case VIR_DOMAIN_DISK_CACHE_WRITETHRU:
+        *writeback = false;
+        *direct = false;
+        *noflush = false;
+        break;
+
+    case VIR_DOMAIN_DISK_CACHE_WRITEBACK:
+        *writeback = true;
+        *direct = false;
+        *noflush = false;
+        break;
+
+    case VIR_DOMAIN_DISK_CACHE_DIRECTSYNC:
+        *writeback = false;
+        *direct = true;
+        *noflush = false;
+        break;
+
+    case VIR_DOMAIN_DISK_CACHE_UNSAFE:
+        *writeback = true;
+        *direct = false;
+        *noflush = true;
+        break;
+
+    case VIR_DOMAIN_DISK_CACHE_DEFAULT:
+    case VIR_DOMAIN_DISK_CACHE_LAST:
+    default:
+        virReportEnumRangeError(virDomainDiskCache, cachemode);
+        return -1;
+    }
+
+    return 0;
+}
+
+
 void
 qemuProcessEventFree(struct qemuProcessEvent *event)
 {

src/qemu/qemu_domain.h

@@ -994,4 +994,10 @@ qemuDomainPrepareDiskSource(virDomainDiskDefPtr disk,
                             qemuDomainObjPrivatePtr priv,
                             virQEMUDriverConfigPtr cfg);
 
+int
+qemuDomainDiskCachemodeFlags(int cachemode,
+                             bool *writeback,
+                             bool *direct,
+                             bool *noflush);
+
 #endif /* __QEMU_DOMAIN_H__ */