[PATCH 1/1] qemu: allow changing disk driver parameters while blockcopying

[jshen28 <yshxxsjt715@xxxxxxx>]

QEMU blockdev allows to configure cachemode, discard and detect-zeroes
for blockdev-add. The benefit of allowing to change cachemode is copying
a shared storage (RBD, writeback) to a local device mapping (SAN, none
cache) and still allows live migration. Allowing changing detect-zeroes
could be beneficial while copying from SAN to RBD without taking too
much space.

Signed-off-by: jshen28 <yshxxsjt715@xxxxxxx>
---
 src/conf/domain_conf.c         | 11 +++++++++++
 src/conf/storage_source_conf.h |  6 +++---
 src/qemu/qemu_blockjob.c       | 13 +++++++++++++
 src/qemu/qemu_driver.c         | 14 ++++++++++++++
 4 files changed, 41 insertions(+), 3 deletions(-)

diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index ff1c78ecd1..0533a770c3 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -13962,6 +13962,17 @@ virDomainDiskDefParseSource(const char *xmlStr,
     if ((driverNode = virXPathNode("./driver", ctxt))) {
         if (virDomainDiskDefDriverSourceParseXML(src, driverNode, ctxt) < 0)
             return NULL;
+        if (virXMLPropEnum(driverNode, "cache", virDomainDiskCacheTypeFromString,
+                           VIR_XML_PROP_NONE, &src->cachemode) < 0)
+            return NULL;
+        if (virXMLPropEnum(driverNode, "detect_zeroes",
+              virDomainDiskDetectZeroesTypeFromString,
+              VIR_XML_PROP_NONE, &src->detect_zeroes) < 0)
+            return NULL;
+        if (virXMLPropEnum(driverNode, "discard",
+              virDomainDiskDiscardTypeFromString,
+              VIR_XML_PROP_NONE, &src->discard) < 0)
+            return NULL;
     }
 
     if (virStorageSourceIsEmpty(src)) {
diff --git a/src/conf/storage_source_conf.h b/src/conf/storage_source_conf.h
index 14a6825d54..bed3b6570d 100644
--- a/src/conf/storage_source_conf.h
+++ b/src/conf/storage_source_conf.h
@@ -392,9 +392,9 @@ struct _virStorageSource {
      * These instances are currently just copies from the parent definition and
      * are not mapped back to the XML */
     int iomode; /* enum virDomainDiskIo */
-    int cachemode; /* enum virDomainDiskCache */
-    int discard; /* enum virDomainDiskDiscard */
-    int detect_zeroes; /* enum virDomainDiskDetectZeroes */
+    unsigned int cachemode; /* enum virDomainDiskCache */
+    unsigned int discard; /* enum virDomainDiskDiscard */
+    unsigned int detect_zeroes; /* enum virDomainDiskDetectZeroes */
 
     bool floppyimg; /* set to true if the storage source is going to be used
                        as a source for floppy drive */
diff --git a/src/qemu/qemu_blockjob.c b/src/qemu/qemu_blockjob.c
index cb2d05d71d..f6b85772be 100644
--- a/src/qemu/qemu_blockjob.c
+++ b/src/qemu/qemu_blockjob.c
@@ -1240,6 +1240,19 @@ qemuBlockJobProcessEventConcludedCopyPivot(virQEMUDriver *driver,
     qemuBlockJobEventProcessConcludedRemoveChain(driver, vm, asyncJob, job->disk->src);
     virObjectUnref(job->disk->src);
     job->disk->src = g_steal_pointer(&job->disk->mirror);
+
+    /* reset cachemode, discard, detect_zeroes to  reflect the enforced setting */
+    if (job->disk->src->cachemode) {
+        job->disk->cachemode = job->disk->src->cachemode;
+    }
+
+    if (job->disk->src->discard) {
+        job->disk->discard = job->disk->src->discard;
+    }
+
+    if (job->disk->src->detect_zeroes) {
+        job->disk->detect_zeroes = job->disk->src->detect_zeroes;
+    }
 }
 
 
diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 6154fe9bfe..4058cdfafe 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -14552,6 +14552,7 @@ qemuDomainBlockCopyCommon(virDomainObj *vm,
     bool existing = mirror_reuse;
     qemuBlockJobData *job = NULL;
     g_autoptr(virStorageSource) mirror = mirrorsrc;
+    g_autoptr(virStorageSource) mirror_cpy = virStorageSourceCopy(mirror, false);
     bool supports_create = false;
     bool supports_access = false;
     bool supports_detect = false;
@@ -14725,6 +14726,19 @@ qemuDomainBlockCopyCommon(virDomainObj *vm,
      * to modify all callers of 'qemuDomainPrepareStorageSourceBlockdev' */
     mirror->detect_zeroes = disk->detect_zeroes;
 
+    /* respect input disk configuration */
+    if (mirror_cpy->detect_zeroes) {
+        mirror->detect_zeroes = mirror_cpy->detect_zeroes;
+    }
+
+    if (mirror_cpy->cachemode) {
+        mirror->cachemode = mirror_cpy->cachemode;
+    }
+
+    if (mirror_cpy->discard) {
+        mirror->discard = mirror_cpy->discard;
+    }
+
     /* If reusing an external image that includes a backing file but the user
      * did not enumerate the chain in the XML we need to detect the chain */
     if (mirror_reuse &&
-- 
2.17.1