util: refactor storage file checks to allow error reporting

The virStorageFileSupportsSecurityDriver and
virStorageFileSupportsAccess currently just return a boolean
value. This is ok because they don't have any failure scenarios
but a subsequent patch is going to introduce potential failure
scenario. This changes their return type from a boolean to an
int with values -1, 0, 1.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

src/qemu/qemu_domain.c

@@ -7514,19 +7514,24 @@ qemuDomainDetermineDiskChain(virQEMUDriverPtr driver,
 
     /* skip to the end of the chain if there is any */
     while (virStorageSourceHasBacking(src)) {
-        if (report_broken &&
-            virStorageFileSupportsAccess(src)) {
+        if (report_broken) {
+            int rv = virStorageFileSupportsAccess(src);
 
-            if (qemuDomainStorageFileInit(driver, vm, src, disk->src) < 0)
+            if (rv < 0)
                 goto cleanup;
 
-            if (virStorageFileAccess(src, F_OK) < 0) {
-                virStorageFileReportBrokenChain(errno, src, disk->src);
+            if (rv > 0) {
+                if (qemuDomainStorageFileInit(driver, vm, src, disk->src) < 0)
+                    goto cleanup;
+
+                if (virStorageFileAccess(src, F_OK) < 0) {
+                    virStorageFileReportBrokenChain(errno, src, disk->src);
+                    virStorageFileDeinit(src);
+                    goto cleanup;
+                }
+
                 virStorageFileDeinit(src);
-                goto cleanup;
             }
-
-            virStorageFileDeinit(src);
         }
         src = src->backingStore;
     }

src/qemu/qemu_driver.c

@@ -308,9 +308,11 @@ qemuSecurityChownCallback(const virStorageSource *src,
     struct stat sb;
     int save_errno = 0;
     int ret = -1;
+    int rv;
 
-    if (!virStorageFileSupportsSecurityDriver(src))
-        return 0;
+    rv = virStorageFileSupportsSecurityDriver(src);
+    if (rv <= 0)
+        return rv;
 
     if (virStorageSourceIsLocalStorage(src)) {
         /* use direct chmod for local files so that the file doesn't

src/util/virstoragefile.c

@@ -4098,34 +4098,46 @@ virStorageFileIsInitialized(const virStorageSource *src)
 }
 
 
-static virStorageFileBackendPtr
-virStorageFileGetBackendForSupportCheck(const virStorageSource *src)
+static int
+virStorageFileGetBackendForSupportCheck(const virStorageSource *src,
+                                        virStorageFileBackendPtr *backend)
 {
     int actualType;
 
-    if (!src)
-        return NULL;
 
-    if (src->drv)
-        return src->drv->backend;
+    if (!src) {
+        *backend = NULL;
+        return 0;
+    }
+
+    if (src->drv) {
+        *backend = src->drv->backend;
+        return 0;
+    }
 
     actualType = virStorageSourceGetActualType(src);
 
-    return virStorageFileBackendForTypeInternal(actualType, src->protocol, false);
+    *backend = virStorageFileBackendForTypeInternal(actualType, src->protocol, false);
+    return 0;
 }
 
 
-static bool
+static int
 virStorageFileSupportsBackingChainTraversal(virStorageSourcePtr src)
 {
     virStorageFileBackendPtr backend;
+    int rv;
 
-    if (!(backend = virStorageFileGetBackendForSupportCheck(src)))
-        return false;
+    rv = virStorageFileGetBackendForSupportCheck(src, &backend);
+    if (rv < 0)
+        return -1;
+
+    if (!backend)
+        return 0;
 
     return backend->storageFileGetUniqueIdentifier &&
            backend->storageFileRead &&
-           backend->storageFileAccess;
+           backend->storageFileAccess ? 1 : 0;
 }
 
 
@@ -4137,15 +4149,19 @@ virStorageFileSupportsBackingChainTraversal(virStorageSourcePtr src)
  * Check if a storage file supports operations needed by the security
  * driver to perform labelling
  */
-bool
+int
 virStorageFileSupportsSecurityDriver(const virStorageSource *src)
 {
     virStorageFileBackendPtr backend;
+    int rv;
 
-    if (!(backend = virStorageFileGetBackendForSupportCheck(src)))
-        return false;
+    rv = virStorageFileGetBackendForSupportCheck(src, &backend);
+    if (rv < 0)
+        return -1;
+    if (backend == NULL)
+        return 0;
 
-    return !!backend->storageFileChown;
+    return backend->storageFileChown ? 1 : 0;
 }
 
 
@@ -4157,15 +4173,19 @@ virStorageFileSupportsSecurityDriver(const virStorageSource *src)
  * Check if a storage file supports checking if the storage source is accessible
  * for the given vm.
  */
-bool
+int
 virStorageFileSupportsAccess(const virStorageSource *src)
 {
     virStorageFileBackendPtr backend;
+    int ret;
 
-    if (!(backend = virStorageFileGetBackendForSupportCheck(src)))
-        return false;
+    ret = virStorageFileGetBackendForSupportCheck(src, &backend);
+    if (ret < 0)
+        return -1;
+    if (backend == NULL)
+        return 0;
 
-    return !!backend->storageFileAccess;
+    return backend->storageFileAccess ? 1 : 0;
 }
 
 
@@ -4514,14 +4534,16 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src,
     ssize_t headerLen;
     virStorageSourcePtr backingStore = NULL;
     int backingFormat;
+    int rv;
 
     VIR_DEBUG("path=%s format=%d uid=%u gid=%u probe=%d",
               src->path, src->format,
               (unsigned int)uid, (unsigned int)gid, allow_probe);
 
     /* exit if we can't load information about the current image */
-    if (!virStorageFileSupportsBackingChainTraversal(src))
-        return 0;
+    rv = virStorageFileSupportsBackingChainTraversal(src);
+    if (rv <= 0)
+        return rv;
 
     if (virStorageFileInitAs(src, uid, gid) < 0)
         return -1;

src/util/virstoragefile.h

@@ -465,8 +465,8 @@ const char *virStorageFileGetUniqueIdentifier(virStorageSourcePtr src);
 int virStorageFileAccess(virStorageSourcePtr src, int mode);
 int virStorageFileChown(const virStorageSource *src, uid_t uid, gid_t gid);
 
-bool virStorageFileSupportsSecurityDriver(const virStorageSource *src);
-bool virStorageFileSupportsAccess(const virStorageSource *src);
+int virStorageFileSupportsSecurityDriver(const virStorageSource *src);
+int virStorageFileSupportsAccess(const virStorageSource *src);
 
 int virStorageFileGetMetadata(virStorageSourcePtr src,
                               uid_t uid, gid_t gid,