storage: Add API to check accessibility of storage volumes

Add a storage driver API equivalent of the access() function.
Implementations for the filesystem and gluster backends are provided.

src/storage/storage_backend.h

@@ -198,6 +198,10 @@ typedef ssize_t
 typedef const char *
 (*virStorageFileBackendGetUniqueIdentifier)(virStorageSourcePtr src);
 
+typedef int
+(*virStorageFileBackendAccess)(virStorageSourcePtr src,
+                               int mode);
+
 virStorageFileBackendPtr virStorageFileBackendForType(int type, int protocol);
 
 
@@ -220,6 +224,7 @@ struct _virStorageFileBackend {
     virStorageFileBackendCreate storageFileCreate;
     virStorageFileBackendUnlink storageFileUnlink;
     virStorageFileBackendStat   storageFileStat;
+    virStorageFileBackendAccess storageFileAccess;
 };
 
 #endif /* __VIR_STORAGE_BACKEND_H__ */

src/storage/storage_backend_fs.c

@@ -1433,6 +1433,15 @@ virStorageFileBackendFileGetUniqueIdentifier(virStorageSourcePtr src)
 }
 
 
+static int
+virStorageFileBackendFileAccess(virStorageSourcePtr src,
+                                int mode)
+{
+    return virFileAccessibleAs(src->path, mode,
+                               src->drv->uid, src->drv->gid);
+}
+
+
 virStorageFileBackend virStorageFileBackendFile = {
     .type = VIR_STORAGE_TYPE_FILE,
 
@@ -1442,6 +1451,7 @@ virStorageFileBackend virStorageFileBackendFile = {
     .storageFileUnlink = virStorageFileBackendFileUnlink,
     .storageFileStat = virStorageFileBackendFileStat,
     .storageFileReadHeader = virStorageFileBackendFileReadHeader,
+    .storageFileAccess = virStorageFileBackendFileAccess,
 
     .storageFileGetUniqueIdentifier = virStorageFileBackendFileGetUniqueIdentifier,
 };
@@ -1455,6 +1465,7 @@ virStorageFileBackend virStorageFileBackendBlock = {
 
     .storageFileStat = virStorageFileBackendFileStat,
     .storageFileReadHeader = virStorageFileBackendFileReadHeader,
+    .storageFileAccess = virStorageFileBackendFileAccess,
 
     .storageFileGetUniqueIdentifier = virStorageFileBackendFileGetUniqueIdentifier,
 };
@@ -1466,6 +1477,8 @@ virStorageFileBackend virStorageFileBackendDir = {
     .backendInit = virStorageFileBackendFileInit,
     .backendDeinit = virStorageFileBackendFileDeinit,
 
+    .storageFileAccess = virStorageFileBackendFileAccess,
+
     .storageFileGetUniqueIdentifier = virStorageFileBackendFileGetUniqueIdentifier,
 };
 

src/storage/storage_backend_gluster.c

@@ -703,6 +703,16 @@ virStorageFileBackendGlusterReadHeader(virStorageSourcePtr src,
 }
 
 
+static int
+virStorageFileBackendGlusterAccess(virStorageSourcePtr src,
+                                   int mode)
+{
+    virStorageFileBackendGlusterPrivPtr priv = src->drv->priv;
+
+    return glfs_access(priv->vol, src->path, mode);
+}
+
+
 virStorageFileBackend virStorageFileBackendGluster = {
     .type = VIR_STORAGE_TYPE_NETWORK,
     .protocol = VIR_STORAGE_NET_PROTOCOL_GLUSTER,
@@ -713,4 +723,5 @@ virStorageFileBackend virStorageFileBackendGluster = {
     .storageFileUnlink = virStorageFileBackendGlusterUnlink,
     .storageFileStat = virStorageFileBackendGlusterStat,
     .storageFileReadHeader = virStorageFileBackendGlusterReadHeader,
+    .storageFileAccess = virStorageFileBackendGlusterAccess,
 };

src/storage/storage_driver.c

@@ -3017,3 +3017,27 @@ virStorageFileGetUniqueIdentifier(virStorageSourcePtr src)
 
     return src->drv->backend->storageFileGetUniqueIdentifier(src);
 }
+
+
+/**
+ * virStorageFileAccess: Check accessibility of a storage file
+ *
+ * @src: storage file to check access permissions
+ * @mode: accessibility check options (see man 2 access)
+ *
+ * Returns 0 on success, -1 on error and sets errno. No libvirt
+ * error is reported. Returns -2 if the operation isn't supported
+ * by libvirt storage backend.
+ */
+int
+virStorageFileAccess(virStorageSourcePtr src,
+                     int mode)
+{
+    if (!virStorageFileIsInitialized(src) ||
+        !src->drv->backend->storageFileAccess) {
+        errno = ENOSYS;
+        return -2;
+    }
+
+    return src->drv->backend->storageFileAccess(src, mode);
+}

src/storage/storage_driver.h

@@ -42,6 +42,7 @@ ssize_t virStorageFileReadHeader(virStorageSourcePtr src,
                                  ssize_t max_len,
                                  char **buf);
 const char *virStorageFileGetUniqueIdentifier(virStorageSourcePtr src);
+int virStorageFileAccess(virStorageSourcePtr src, int mode);
 
 int storageRegister(void);