qemu: domain: Simplify using DAC permissions of top of backing chain

qemuDomainGetImageIds and qemuDomainStorageFileInit are helpful when
trying to access a virStorageSource from the qemu driver since they
figure out the correct uid and gid for the image.

When accessing members of a backing chain the permissions for the top
level would be used. To allow using specific permissions per backing
chain level but still allow inheritance from the parent of the chain we
need to add a new parameter to the image ID APIs.

src/qemu/qemu_domain.c

@@ -5931,6 +5931,7 @@ static void
 qemuDomainGetImageIds(virQEMUDriverConfigPtr cfg,
                       virDomainObjPtr vm,
                       virStorageSourcePtr src,
+                      virStorageSourcePtr parentSrc,
                       uid_t *uid, gid_t *gid)
 {
     virSecurityLabelDefPtr vmlabel;
@@ -5953,6 +5954,11 @@ qemuDomainGetImageIds(virQEMUDriverConfigPtr cfg,
         vmlabel->label)
         virParseOwnershipIds(vmlabel->label, uid, gid);
 
+    if (parentSrc &&
+        (disklabel = virStorageSourceGetSecurityLabelDef(parentSrc, "dac")) &&
+        disklabel->label)
+        virParseOwnershipIds(disklabel->label, uid, gid);
+
     if ((disklabel = virStorageSourceGetSecurityLabelDef(src, "dac")) &&
         disklabel->label)
         virParseOwnershipIds(disklabel->label, uid, gid);
@@ -5962,14 +5968,15 @@ qemuDomainGetImageIds(virQEMUDriverConfigPtr cfg,
 int
 qemuDomainStorageFileInit(virQEMUDriverPtr driver,
                           virDomainObjPtr vm,
-                          virStorageSourcePtr src)
+                          virStorageSourcePtr src,
+                          virStorageSourcePtr parent)
 {
     virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
     uid_t uid;
     gid_t gid;
     int ret = -1;
 
-    qemuDomainGetImageIds(cfg, vm, src, &uid, &gid);
+    qemuDomainGetImageIds(cfg, vm, src, parent, &uid, &gid);
 
     if (virStorageFileInitAs(src, uid, gid) < 0)
         goto cleanup;
@@ -6019,7 +6026,7 @@ qemuDomainDetermineDiskChain(virQEMUDriverPtr driver,
             goto cleanup;
     }
 
-    qemuDomainGetImageIds(cfg, vm, disk->src, &uid, &gid);
+    qemuDomainGetImageIds(cfg, vm, disk->src, NULL, &uid, &gid);
 
     if (virStorageFileGetMetadata(disk->src,
                                   uid, gid,

src/qemu/qemu_domain.h

@@ -679,7 +679,8 @@ bool qemuDomainDiskChangeSupported(virDomainDiskDefPtr disk,
 
 int qemuDomainStorageFileInit(virQEMUDriverPtr driver,
                               virDomainObjPtr vm,
-                              virStorageSourcePtr src);
+                              virStorageSourcePtr src,
+                              virStorageSourcePtr parent);
 char *qemuDomainStorageAlias(const char *device, int depth);
 
 void qemuDomainDiskChainElementRevoke(virQEMUDriverPtr driver,

src/qemu/qemu_driver.c

@@ -11520,7 +11520,7 @@ qemuDomainBlockPeek(virDomainPtr dom,
         goto cleanup;
     }
 
-    if (qemuDomainStorageFileInit(driver, vm, disk->src) < 0)
+    if (qemuDomainStorageFileInit(driver, vm, disk->src, NULL) < 0)
         goto cleanup;
 
     if ((nread = virStorageFileRead(disk->src, offset, size, &tmpbuf)) < 0)
@@ -14437,7 +14437,7 @@ qemuDomainSnapshotDiskDataCollect(virQEMUDriverPtr driver,
         if (virStorageSourceInitChainElement(dd->src, dd->disk->src, false) < 0)
             goto error;
 
-        if (qemuDomainStorageFileInit(driver, vm, dd->src) < 0)
+        if (qemuDomainStorageFileInit(driver, vm, dd->src, NULL) < 0)
             goto error;
 
         dd->initialized = true;
@@ -17112,7 +17112,7 @@ qemuDomainBlockCopyCommon(virDomainObjPtr vm,
         goto endjob;
     }
 
-    if (qemuDomainStorageFileInit(driver, vm, mirror) < 0)
+    if (qemuDomainStorageFileInit(driver, vm, mirror, NULL) < 0)
         goto endjob;
 
     if (qemuDomainBlockCopyValidateMirror(mirror, disk->dst, &reuse) < 0)