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[libvirt] [PATCH 3/6] storage: Split out virStorageSource accessors to separate file



The helper methods for actually accessing the storage objects don't
really belong to the main storage driver implementation file. Split them
out.
---
 po/POTFILES.in                |   1 +
 src/Makefile.am               |   1 +
 src/qemu/qemu_domain.c        |   1 +
 src/qemu/qemu_driver.c        |   1 +
 src/security/virt-aa-helper.c |   2 +-
 src/storage/storage_driver.c  | 551 +--------------------------------------
 src/storage/storage_driver.h  |  28 --
 src/storage/storage_source.c  | 585 ++++++++++++++++++++++++++++++++++++++++++
 src/storage/storage_source.h  |  53 ++++
 tests/virstoragetest.c        |   1 +
 10 files changed, 645 insertions(+), 579 deletions(-)
 create mode 100644 src/storage/storage_source.c
 create mode 100644 src/storage/storage_source.h

diff --git a/po/POTFILES.in b/po/POTFILES.in
index 275df1f29..87634d228 100644
--- a/po/POTFILES.in
+++ b/po/POTFILES.in
@@ -185,6 +185,7 @@ src/storage/storage_backend_sheepdog.c
 src/storage/storage_backend_vstorage.c
 src/storage/storage_backend_zfs.c
 src/storage/storage_driver.c
+src/storage/storage_source.c
 src/storage/storage_util.c
 src/test/test_driver.c
 src/uml/uml_conf.c
diff --git a/src/Makefile.am b/src/Makefile.am
index eae32dc58..399d031dd 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -1053,6 +1053,7 @@ STORAGE_DRIVER_BACKEND_SOURCES = \

 STORAGE_DRIVER_SOURCES =						\
 		storage/storage_driver.h storage/storage_driver.c	\
+		storage/storage_source.h storage/storage_source.c	\
 		$(STORAGE_DRIVER_BACKEND_SOURCES) \
 		storage/storage_util.h storage/storage_util.c

diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index 8e7404da6..bc3a85ca2 100644
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -54,6 +54,7 @@
 #include "locking/domain_lock.h"

 #include "storage/storage_driver.h"
+#include "storage/storage_source.h"

 #ifdef MAJOR_IN_MKDEV
 # include <sys/mkdev.h>
diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index e91663ca9..052c7f0fc 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -100,6 +100,7 @@
 #include "viraccessapicheck.h"
 #include "viraccessapicheckqemu.h"
 #include "storage/storage_driver.h"
+#include "storage/storage_source.h"
 #include "virhostdev.h"
 #include "domain_capabilities.h"
 #include "vircgroup.h"
diff --git a/src/security/virt-aa-helper.c b/src/security/virt-aa-helper.c
index 7f3b7ad08..695272076 100644
--- a/src/security/virt-aa-helper.c
+++ b/src/security/virt-aa-helper.c
@@ -55,7 +55,7 @@
 #include "virstring.h"
 #include "virgettext.h"

-#include "storage/storage_driver.h"
+#include "storage/storage_source.h"

 #define VIR_FROM_THIS VIR_FROM_SECURITY

diff --git a/src/storage/storage_driver.c b/src/storage/storage_driver.c
index ab1dc8f36..ffffd5a37 100644
--- a/src/storage/storage_driver.c
+++ b/src/storage/storage_driver.c
@@ -50,7 +50,7 @@
 #include "configmake.h"
 #include "virstring.h"
 #include "viraccessapicheck.h"
-#include "dirname.h"
+//#include "dirname.h"
 #include "storage_util.h"

 #define VIR_FROM_THIS VIR_FROM_STORAGE
@@ -2758,555 +2758,6 @@ storageRegisterAll(void)
 }


-/* ----------- file handlers cooperating with storage driver --------------- */
-static bool
-virStorageFileIsInitialized(const virStorageSource *src)
-{
-    return src && src->drv;
-}
-
-
-static bool
-virStorageFileSupportsBackingChainTraversal(virStorageSourcePtr src)
-{
-    int actualType;
-    virStorageFileBackendPtr backend;
-
-    if (!src)
-        return false;
-    actualType = virStorageSourceGetActualType(src);
-
-    if (src->drv) {
-        backend = src->drv->backend;
-    } else {
-        if (!(backend = virStorageFileBackendForTypeInternal(actualType,
-                                                             src->protocol,
-                                                             false)))
-            return false;
-    }
-
-    return backend->storageFileGetUniqueIdentifier &&
-           backend->storageFileReadHeader &&
-           backend->storageFileAccess;
-}
-
-
-/**
- * virStorageFileSupportsSecurityDriver:
- *
- * @src: a storage file structure
- *
- * Check if a storage file supports operations needed by the security
- * driver to perform labelling
- */
-bool
-virStorageFileSupportsSecurityDriver(const virStorageSource *src)
-{
-    int actualType;
-    virStorageFileBackendPtr backend;
-
-    if (!src)
-        return false;
-    actualType = virStorageSourceGetActualType(src);
-
-    if (src->drv) {
-        backend = src->drv->backend;
-    } else {
-        if (!(backend = virStorageFileBackendForTypeInternal(actualType,
-                                                             src->protocol,
-                                                             false)))
-            return false;
-    }
-
-    return !!backend->storageFileChown;
-}
-
-
-void
-virStorageFileDeinit(virStorageSourcePtr src)
-{
-    if (!virStorageFileIsInitialized(src))
-        return;
-
-    if (src->drv->backend &&
-        src->drv->backend->backendDeinit)
-        src->drv->backend->backendDeinit(src);
-
-    VIR_FREE(src->drv);
-}
-
-
-/**
- * virStorageFileInitAs:
- *
- * @src: storage source definition
- * @uid: uid used to access the file, or -1 for current uid
- * @gid: gid used to access the file, or -1 for current gid
- *
- * Initialize a storage source to be used with storage driver. Use the provided
- * uid and gid if possible for the operations.
- *
- * Returns 0 if the storage file was successfully initialized, -1 if the
- * initialization failed. Libvirt error is reported.
- */
-int
-virStorageFileInitAs(virStorageSourcePtr src,
-                     uid_t uid, gid_t gid)
-{
-    int actualType = virStorageSourceGetActualType(src);
-    if (VIR_ALLOC(src->drv) < 0)
-        return -1;
-
-    if (uid == (uid_t) -1)
-        src->drv->uid = geteuid();
-    else
-        src->drv->uid = uid;
-
-    if (gid == (gid_t) -1)
-        src->drv->gid = getegid();
-    else
-        src->drv->gid = gid;
-
-    if (!(src->drv->backend = virStorageFileBackendForType(actualType,
-                                                           src->protocol)))
-        goto error;
-
-    if (src->drv->backend->backendInit &&
-        src->drv->backend->backendInit(src) < 0)
-        goto error;
-
-    return 0;
-
- error:
-    VIR_FREE(src->drv);
-    return -1;
-}
-
-
-/**
- * virStorageFileInit:
- *
- * See virStorageFileInitAs. The file is initialized to be accessed by the
- * current user.
- */
-int
-virStorageFileInit(virStorageSourcePtr src)
-{
-    return virStorageFileInitAs(src, -1, -1);
-}
-
-
-/**
- * virStorageFileCreate: Creates an empty storage file via storage driver
- *
- * @src: file structure pointing to the file
- *
- * Returns 0 on success, -2 if the function isn't supported by the backend,
- * -1 on other failure. Errno is set in case of failure.
- */
-int
-virStorageFileCreate(virStorageSourcePtr src)
-{
-    int ret;
-
-    if (!virStorageFileIsInitialized(src) ||
-        !src->drv->backend->storageFileCreate) {
-        errno = ENOSYS;
-        return -2;
-    }
-
-    ret = src->drv->backend->storageFileCreate(src);
-
-    VIR_DEBUG("created storage file %p: ret=%d, errno=%d",
-              src, ret, errno);
-
-    return ret;
-}
-
-
-/**
- * virStorageFileUnlink: Unlink storage file via storage driver
- *
- * @src: file structure pointing to the file
- *
- * Unlinks the file described by the @file structure.
- *
- * Returns 0 on success, -2 if the function isn't supported by the backend,
- * -1 on other failure. Errno is set in case of failure.
- */
-int
-virStorageFileUnlink(virStorageSourcePtr src)
-{
-    int ret;
-
-    if (!virStorageFileIsInitialized(src) ||
-        !src->drv->backend->storageFileUnlink) {
-        errno = ENOSYS;
-        return -2;
-    }
-
-    ret = src->drv->backend->storageFileUnlink(src);
-
-    VIR_DEBUG("unlinked storage file %p: ret=%d, errno=%d",
-              src, ret, errno);
-
-    return ret;
-}
-
-
-/**
- * virStorageFileStat: returns stat struct of a file via storage driver
- *
- * @src: file structure pointing to the file
- * @stat: stat structure to return data
- *
- * Returns 0 on success, -2 if the function isn't supported by the backend,
- * -1 on other failure. Errno is set in case of failure.
-*/
-int
-virStorageFileStat(virStorageSourcePtr src,
-                   struct stat *st)
-{
-    int ret;
-
-    if (!virStorageFileIsInitialized(src) ||
-        !src->drv->backend->storageFileStat) {
-        errno = ENOSYS;
-        return -2;
-    }
-
-    ret = src->drv->backend->storageFileStat(src, st);
-
-    VIR_DEBUG("stat of storage file %p: ret=%d, errno=%d",
-              src, ret, errno);
-
-    return ret;
-}
-
-
-/**
- * virStorageFileReadHeader: read the beginning bytes of a file into a buffer
- *
- * @src: file structure pointing to the file
- * @max_len: maximum number of bytes read from the storage file
- * @buf: buffer to read the data into. buffer shall be freed by caller)
- *
- * Returns the count of bytes read on success and -1 on failure, -2 if the
- * function isn't supported by the backend.
- * Libvirt error is reported on failure.
- */
-ssize_t
-virStorageFileReadHeader(virStorageSourcePtr src,
-                         ssize_t max_len,
-                         char **buf)
-{
-    ssize_t ret;
-
-    if (!virStorageFileIsInitialized(src)) {
-        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                       _("storage file backend not initialized"));
-        return -1;
-    }
-
-    if (!src->drv->backend->storageFileReadHeader) {
-        virReportError(VIR_ERR_INTERNAL_ERROR,
-                       _("storage file header reading is not supported for "
-                         "storage type %s (protocol: %s)"),
-                       virStorageTypeToString(src->type),
-                       virStorageNetProtocolTypeToString(src->protocol));
-        return -2;
-    }
-
-    ret = src->drv->backend->storageFileReadHeader(src, max_len, buf);
-
-    VIR_DEBUG("read of storage header %p: ret=%zd", src, ret);
-
-    return ret;
-}
-
-
-/*
- * virStorageFileGetUniqueIdentifier: Get a unique string describing the volume
- *
- * @src: file structure pointing to the file
- *
- * Returns a string uniquely describing a single volume (canonical path).
- * The string shall not be freed and is valid until the storage file is
- * deinitialized. Returns NULL on error and sets a libvirt error code */
-const char *
-virStorageFileGetUniqueIdentifier(virStorageSourcePtr src)
-{
-    if (!virStorageFileIsInitialized(src)) {
-        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                       _("storage file backend not initialized"));
-        return NULL;
-    }
-
-    if (!src->drv->backend->storageFileGetUniqueIdentifier) {
-        virReportError(VIR_ERR_INTERNAL_ERROR,
-                       _("unique storage file identifier not implemented for "
-                          "storage type %s (protocol: %s)'"),
-                       virStorageTypeToString(src->type),
-                       virStorageNetProtocolTypeToString(src->protocol));
-        return NULL;
-    }
-
-    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);
-}
-
-
-/**
- * virStorageFileChown: Change owner of a storage file
- *
- * @src: storage file to change owner of
- * @uid: new owner id
- * @gid: new group id
- *
- * 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
-virStorageFileChown(const virStorageSource *src,
-                    uid_t uid,
-                    gid_t gid)
-{
-    if (!virStorageFileIsInitialized(src) ||
-        !src->drv->backend->storageFileChown) {
-        errno = ENOSYS;
-        return -2;
-    }
-
-    VIR_DEBUG("chown of storage file %p to %u:%u",
-              src, (unsigned int)uid, (unsigned int)gid);
-
-    return src->drv->backend->storageFileChown(src, uid, gid);
-}
-
-
-/* Recursive workhorse for virStorageFileGetMetadata.  */
-static int
-virStorageFileGetMetadataRecurse(virStorageSourcePtr src,
-                                 virStorageSourcePtr parent,
-                                 uid_t uid, gid_t gid,
-                                 bool allow_probe,
-                                 bool report_broken,
-                                 virHashTablePtr cycle)
-{
-    int ret = -1;
-    const char *uniqueName;
-    char *buf = NULL;
-    ssize_t headerLen;
-    virStorageSourcePtr backingStore = NULL;
-    int backingFormat;
-
-    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;
-
-    if (virStorageFileInitAs(src, uid, gid) < 0)
-        return -1;
-
-    if (virStorageFileAccess(src, F_OK) < 0) {
-        if (src == parent) {
-            virReportSystemError(errno,
-                                 _("Cannot access storage file '%s' "
-                                   "(as uid:%u, gid:%u)"),
-                                 src->path, (unsigned int)uid,
-                                 (unsigned int)gid);
-        } else {
-            virReportSystemError(errno,
-                                 _("Cannot access backing file '%s' "
-                                   "of storage file '%s' (as uid:%u, gid:%u)"),
-                                 src->path, parent->path,
-                                 (unsigned int)uid, (unsigned int)gid);
-        }
-
-        goto cleanup;
-    }
-
-    if (!(uniqueName = virStorageFileGetUniqueIdentifier(src)))
-        goto cleanup;
-
-    if (virHashLookup(cycle, uniqueName)) {
-        virReportError(VIR_ERR_INTERNAL_ERROR,
-                       _("backing store for %s (%s) is self-referential"),
-                       src->path, uniqueName);
-        goto cleanup;
-    }
-
-    if (virHashAddEntry(cycle, uniqueName, (void *)1) < 0)
-        goto cleanup;
-
-    if ((headerLen = virStorageFileReadHeader(src, VIR_STORAGE_MAX_HEADER,
-                                              &buf)) < 0)
-        goto cleanup;
-
-    if (virStorageFileGetMetadataInternal(src, buf, headerLen,
-                                          &backingFormat) < 0)
-        goto cleanup;
-
-    /* check whether we need to go deeper */
-    if (!src->backingStoreRaw) {
-        ret = 0;
-        goto cleanup;
-    }
-
-    if (!(backingStore = virStorageSourceNewFromBacking(src)))
-        goto cleanup;
-
-    if (backingFormat == VIR_STORAGE_FILE_AUTO && !allow_probe)
-        backingStore->format = VIR_STORAGE_FILE_RAW;
-    else if (backingFormat == VIR_STORAGE_FILE_AUTO_SAFE)
-        backingStore->format = VIR_STORAGE_FILE_AUTO;
-    else
-        backingStore->format = backingFormat;
-
-    if ((ret = virStorageFileGetMetadataRecurse(backingStore, parent,
-                                                uid, gid,
-                                                allow_probe, report_broken,
-                                                cycle)) < 0) {
-        if (report_broken)
-            goto cleanup;
-
-        /* if we fail somewhere midway, just accept and return a
-         * broken chain */
-        ret = 0;
-        goto cleanup;
-    }
-
-    src->backingStore = backingStore;
-    backingStore = NULL;
-    ret = 0;
-
- cleanup:
-    VIR_FREE(buf);
-    virStorageFileDeinit(src);
-    virStorageSourceFree(backingStore);
-    return ret;
-}
-
-
-/**
- * virStorageFileGetMetadata:
- *
- * Extract metadata about the storage volume with the specified
- * image format. If image format is VIR_STORAGE_FILE_AUTO, it
- * will probe to automatically identify the format.  Recurses through
- * the entire chain.
- *
- * Open files using UID and GID (or pass -1 for the current user/group).
- * Treat any backing files without explicit type as raw, unless ALLOW_PROBE.
- *
- * Callers are advised never to use VIR_STORAGE_FILE_AUTO as a
- * format, since a malicious guest can turn a raw file into any
- * other non-raw format at will.
- *
- * If @report_broken is true, the whole function fails with a possibly sane
- * error instead of just returning a broken chain.
- *
- * Caller MUST free result after use via virStorageSourceFree.
- */
-int
-virStorageFileGetMetadata(virStorageSourcePtr src,
-                          uid_t uid, gid_t gid,
-                          bool allow_probe,
-                          bool report_broken)
-{
-    VIR_DEBUG("path=%s format=%d uid=%u gid=%u probe=%d, report_broken=%d",
-              src->path, src->format, (unsigned int)uid, (unsigned int)gid,
-              allow_probe, report_broken);
-
-    virHashTablePtr cycle = NULL;
-    int ret = -1;
-
-    if (!(cycle = virHashCreate(5, NULL)))
-        return -1;
-
-    if (src->format <= VIR_STORAGE_FILE_NONE)
-        src->format = allow_probe ?
-            VIR_STORAGE_FILE_AUTO : VIR_STORAGE_FILE_RAW;
-
-    ret = virStorageFileGetMetadataRecurse(src, src, uid, gid,
-                                           allow_probe, report_broken, cycle);
-
-    virHashFree(cycle);
-    return ret;
-}
-
-
-/**
- * virStorageFileGetBackingStoreStr:
- * @src: storage object
- *
- * Extracts the backing store string as stored in the storage volume described
- * by @src and returns it to the user. Caller is responsible for freeing it.
- * In case when the string can't be retrieved or does not exist NULL is
- * returned.
- */
-char *
-virStorageFileGetBackingStoreStr(virStorageSourcePtr src)
-{
-    virStorageSourcePtr tmp = NULL;
-    char *buf = NULL;
-    ssize_t headerLen;
-    char *ret = NULL;
-
-    /* exit if we can't load information about the current image */
-    if (!virStorageFileSupportsBackingChainTraversal(src))
-        return NULL;
-
-    if (virStorageFileAccess(src, F_OK) < 0)
-        return NULL;
-
-    if ((headerLen = virStorageFileReadHeader(src, VIR_STORAGE_MAX_HEADER,
-                                              &buf)) < 0)
-        return NULL;
-
-    if (!(tmp = virStorageSourceCopy(src, false)))
-        goto cleanup;
-
-    if (virStorageFileGetMetadataInternal(tmp, buf, headerLen, NULL) < 0)
-        goto cleanup;
-
-    VIR_STEAL_PTR(ret, tmp->backingStoreRaw);
-
- cleanup:
-    VIR_FREE(buf);
-    virStorageSourceFree(tmp);
-
-    return ret;
-}
-
-
 static int
 virStorageAddISCSIPoolSourceHost(virDomainDiskDefPtr def,
                                  virStoragePoolDefPtr pooldef)
diff --git a/src/storage/storage_driver.h b/src/storage/storage_driver.h
index ade05f715..8b913a1b8 100644
--- a/src/storage/storage_driver.h
+++ b/src/storage/storage_driver.h
@@ -28,34 +28,6 @@

 # include "domain_conf.h"
 # include "virstorageobj.h"
-# include "virstoragefile.h"
-
-int virStorageFileInit(virStorageSourcePtr src);
-int virStorageFileInitAs(virStorageSourcePtr src,
-                         uid_t uid, gid_t gid);
-void virStorageFileDeinit(virStorageSourcePtr src);
-
-int virStorageFileCreate(virStorageSourcePtr src);
-int virStorageFileUnlink(virStorageSourcePtr src);
-int virStorageFileStat(virStorageSourcePtr src,
-                       struct stat *stat);
-ssize_t virStorageFileReadHeader(virStorageSourcePtr src,
-                                 ssize_t max_len,
-                                 char **buf);
-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);
-
-int virStorageFileGetMetadata(virStorageSourcePtr src,
-                              uid_t uid, gid_t gid,
-                              bool allow_probe,
-                              bool report_broken)
-    ATTRIBUTE_NONNULL(1);
-
-char *virStorageFileGetBackingStoreStr(virStorageSourcePtr src)
-    ATTRIBUTE_NONNULL(1);

 int virStorageTranslateDiskSourcePool(virConnectPtr conn,
                                       virDomainDiskDefPtr def);
diff --git a/src/storage/storage_source.c b/src/storage/storage_source.c
new file mode 100644
index 000000000..c91d629c8
--- /dev/null
+++ b/src/storage/storage_source.c
@@ -0,0 +1,585 @@
+/*
+ * storage_source.c: Storage source object accessors to real storage
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library.  If not, see
+ * <http://www.gnu.org/licenses/>.
+ */
+
+#include <config.h>
+
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#include <errno.h>
+#include <string.h>
+
+#include "virerror.h"
+#include "storage_source.h"
+#include "storage_backend.h"
+#include "viralloc.h"
+#include "virlog.h"
+#include "virstring.h"
+#include "virhash.h"
+
+#define VIR_FROM_THIS VIR_FROM_STORAGE
+
+VIR_LOG_INIT("storage.storage_source");
+
+
+static bool
+virStorageFileIsInitialized(const virStorageSource *src)
+{
+    return src && src->drv;
+}
+
+
+static bool
+virStorageFileSupportsBackingChainTraversal(virStorageSourcePtr src)
+{
+    int actualType;
+    virStorageFileBackendPtr backend;
+
+    if (!src)
+        return false;
+    actualType = virStorageSourceGetActualType(src);
+
+    if (src->drv) {
+        backend = src->drv->backend;
+    } else {
+        if (!(backend = virStorageFileBackendForTypeInternal(actualType,
+                                                             src->protocol,
+                                                             false)))
+            return false;
+    }
+
+    return backend->storageFileGetUniqueIdentifier &&
+           backend->storageFileReadHeader &&
+           backend->storageFileAccess;
+}
+
+
+/**
+ * virStorageFileSupportsSecurityDriver:
+ *
+ * @src: a storage file structure
+ *
+ * Check if a storage file supports operations needed by the security
+ * driver to perform labelling
+ */
+bool
+virStorageFileSupportsSecurityDriver(const virStorageSource *src)
+{
+    int actualType;
+    virStorageFileBackendPtr backend;
+
+    if (!src)
+        return false;
+    actualType = virStorageSourceGetActualType(src);
+
+    if (src->drv) {
+        backend = src->drv->backend;
+    } else {
+        if (!(backend = virStorageFileBackendForTypeInternal(actualType,
+                                                             src->protocol,
+                                                             false)))
+            return false;
+    }
+
+    return !!backend->storageFileChown;
+}
+
+
+void
+virStorageFileDeinit(virStorageSourcePtr src)
+{
+    if (!virStorageFileIsInitialized(src))
+        return;
+
+    if (src->drv->backend &&
+        src->drv->backend->backendDeinit)
+        src->drv->backend->backendDeinit(src);
+
+    VIR_FREE(src->drv);
+}
+
+
+/**
+ * virStorageFileInitAs:
+ *
+ * @src: storage source definition
+ * @uid: uid used to access the file, or -1 for current uid
+ * @gid: gid used to access the file, or -1 for current gid
+ *
+ * Initialize a storage source to be used with storage driver. Use the provided
+ * uid and gid if possible for the operations.
+ *
+ * Returns 0 if the storage file was successfully initialized, -1 if the
+ * initialization failed. Libvirt error is reported.
+ */
+int
+virStorageFileInitAs(virStorageSourcePtr src,
+                     uid_t uid, gid_t gid)
+{
+    int actualType = virStorageSourceGetActualType(src);
+    if (VIR_ALLOC(src->drv) < 0)
+        return -1;
+
+    if (uid == (uid_t) -1)
+        src->drv->uid = geteuid();
+    else
+        src->drv->uid = uid;
+
+    if (gid == (gid_t) -1)
+        src->drv->gid = getegid();
+    else
+        src->drv->gid = gid;
+
+    if (!(src->drv->backend = virStorageFileBackendForType(actualType,
+                                                           src->protocol)))
+        goto error;
+
+    if (src->drv->backend->backendInit &&
+        src->drv->backend->backendInit(src) < 0)
+        goto error;
+
+    return 0;
+
+ error:
+    VIR_FREE(src->drv);
+    return -1;
+}
+
+
+/**
+ * virStorageFileInit:
+ *
+ * See virStorageFileInitAs. The file is initialized to be accessed by the
+ * current user.
+ */
+int
+virStorageFileInit(virStorageSourcePtr src)
+{
+    return virStorageFileInitAs(src, -1, -1);
+}
+
+
+/**
+ * virStorageFileCreate: Creates an empty storage file via storage driver
+ *
+ * @src: file structure pointing to the file
+ *
+ * Returns 0 on success, -2 if the function isn't supported by the backend,
+ * -1 on other failure. Errno is set in case of failure.
+ */
+int
+virStorageFileCreate(virStorageSourcePtr src)
+{
+    int ret;
+
+    if (!virStorageFileIsInitialized(src) ||
+        !src->drv->backend->storageFileCreate) {
+        errno = ENOSYS;
+        return -2;
+    }
+
+    ret = src->drv->backend->storageFileCreate(src);
+
+    VIR_DEBUG("created storage file %p: ret=%d, errno=%d",
+              src, ret, errno);
+
+    return ret;
+}
+
+
+/**
+ * virStorageFileUnlink: Unlink storage file via storage driver
+ *
+ * @src: file structure pointing to the file
+ *
+ * Unlinks the file described by the @file structure.
+ *
+ * Returns 0 on success, -2 if the function isn't supported by the backend,
+ * -1 on other failure. Errno is set in case of failure.
+ */
+int
+virStorageFileUnlink(virStorageSourcePtr src)
+{
+    int ret;
+
+    if (!virStorageFileIsInitialized(src) ||
+        !src->drv->backend->storageFileUnlink) {
+        errno = ENOSYS;
+        return -2;
+    }
+
+    ret = src->drv->backend->storageFileUnlink(src);
+
+    VIR_DEBUG("unlinked storage file %p: ret=%d, errno=%d",
+              src, ret, errno);
+
+    return ret;
+}
+
+
+/**
+ * virStorageFileStat: returns stat struct of a file via storage driver
+ *
+ * @src: file structure pointing to the file
+ * @stat: stat structure to return data
+ *
+ * Returns 0 on success, -2 if the function isn't supported by the backend,
+ * -1 on other failure. Errno is set in case of failure.
+*/
+int
+virStorageFileStat(virStorageSourcePtr src,
+                   struct stat *st)
+{
+    int ret;
+
+    if (!virStorageFileIsInitialized(src) ||
+        !src->drv->backend->storageFileStat) {
+        errno = ENOSYS;
+        return -2;
+    }
+
+    ret = src->drv->backend->storageFileStat(src, st);
+
+    VIR_DEBUG("stat of storage file %p: ret=%d, errno=%d",
+              src, ret, errno);
+
+    return ret;
+}
+
+
+/**
+ * virStorageFileReadHeader: read the beginning bytes of a file into a buffer
+ *
+ * @src: file structure pointing to the file
+ * @max_len: maximum number of bytes read from the storage file
+ * @buf: buffer to read the data into. buffer shall be freed by caller)
+ *
+ * Returns the count of bytes read on success and -1 on failure, -2 if the
+ * function isn't supported by the backend.
+ * Libvirt error is reported on failure.
+ */
+ssize_t
+virStorageFileReadHeader(virStorageSourcePtr src,
+                         ssize_t max_len,
+                         char **buf)
+{
+    ssize_t ret;
+
+    if (!virStorageFileIsInitialized(src)) {
+        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                       _("storage file backend not initialized"));
+        return -1;
+    }
+
+    if (!src->drv->backend->storageFileReadHeader) {
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("storage file header reading is not supported for "
+                         "storage type %s (protocol: %s)"),
+                       virStorageTypeToString(src->type),
+                       virStorageNetProtocolTypeToString(src->protocol));
+        return -2;
+    }
+
+    ret = src->drv->backend->storageFileReadHeader(src, max_len, buf);
+
+    VIR_DEBUG("read of storage header %p: ret=%zd", src, ret);
+
+    return ret;
+}
+
+
+/*
+ * virStorageFileGetUniqueIdentifier: Get a unique string describing the volume
+ *
+ * @src: file structure pointing to the file
+ *
+ * Returns a string uniquely describing a single volume (canonical path).
+ * The string shall not be freed and is valid until the storage file is
+ * deinitialized. Returns NULL on error and sets a libvirt error code */
+const char *
+virStorageFileGetUniqueIdentifier(virStorageSourcePtr src)
+{
+    if (!virStorageFileIsInitialized(src)) {
+        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                       _("storage file backend not initialized"));
+        return NULL;
+    }
+
+    if (!src->drv->backend->storageFileGetUniqueIdentifier) {
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("unique storage file identifier not implemented for "
+                          "storage type %s (protocol: %s)'"),
+                       virStorageTypeToString(src->type),
+                       virStorageNetProtocolTypeToString(src->protocol));
+        return NULL;
+    }
+
+    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);
+}
+
+
+/**
+ * virStorageFileChown: Change owner of a storage file
+ *
+ * @src: storage file to change owner of
+ * @uid: new owner id
+ * @gid: new group id
+ *
+ * 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
+virStorageFileChown(const virStorageSource *src,
+                    uid_t uid,
+                    gid_t gid)
+{
+    if (!virStorageFileIsInitialized(src) ||
+        !src->drv->backend->storageFileChown) {
+        errno = ENOSYS;
+        return -2;
+    }
+
+    VIR_DEBUG("chown of storage file %p to %u:%u",
+              src, (unsigned int)uid, (unsigned int)gid);
+
+    return src->drv->backend->storageFileChown(src, uid, gid);
+}
+
+
+/* Recursive workhorse for virStorageFileGetMetadata.  */
+static int
+virStorageFileGetMetadataRecurse(virStorageSourcePtr src,
+                                 virStorageSourcePtr parent,
+                                 uid_t uid, gid_t gid,
+                                 bool allow_probe,
+                                 bool report_broken,
+                                 virHashTablePtr cycle)
+{
+    int ret = -1;
+    const char *uniqueName;
+    char *buf = NULL;
+    ssize_t headerLen;
+    virStorageSourcePtr backingStore = NULL;
+    int backingFormat;
+
+    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;
+
+    if (virStorageFileInitAs(src, uid, gid) < 0)
+        return -1;
+
+    if (virStorageFileAccess(src, F_OK) < 0) {
+        if (src == parent) {
+            virReportSystemError(errno,
+                                 _("Cannot access storage file '%s' "
+                                   "(as uid:%u, gid:%u)"),
+                                 src->path, (unsigned int)uid,
+                                 (unsigned int)gid);
+        } else {
+            virReportSystemError(errno,
+                                 _("Cannot access backing file '%s' "
+                                   "of storage file '%s' (as uid:%u, gid:%u)"),
+                                 src->path, parent->path,
+                                 (unsigned int)uid, (unsigned int)gid);
+        }
+
+        goto cleanup;
+    }
+
+    if (!(uniqueName = virStorageFileGetUniqueIdentifier(src)))
+        goto cleanup;
+
+    if (virHashLookup(cycle, uniqueName)) {
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("backing store for %s (%s) is self-referential"),
+                       src->path, uniqueName);
+        goto cleanup;
+    }
+
+    if (virHashAddEntry(cycle, uniqueName, (void *)1) < 0)
+        goto cleanup;
+
+    if ((headerLen = virStorageFileReadHeader(src, VIR_STORAGE_MAX_HEADER,
+                                              &buf)) < 0)
+        goto cleanup;
+
+    if (virStorageFileGetMetadataInternal(src, buf, headerLen,
+                                          &backingFormat) < 0)
+        goto cleanup;
+
+    /* check whether we need to go deeper */
+    if (!src->backingStoreRaw) {
+        ret = 0;
+        goto cleanup;
+    }
+
+    if (!(backingStore = virStorageSourceNewFromBacking(src)))
+        goto cleanup;
+
+    if (backingFormat == VIR_STORAGE_FILE_AUTO && !allow_probe)
+        backingStore->format = VIR_STORAGE_FILE_RAW;
+    else if (backingFormat == VIR_STORAGE_FILE_AUTO_SAFE)
+        backingStore->format = VIR_STORAGE_FILE_AUTO;
+    else
+        backingStore->format = backingFormat;
+
+    if ((ret = virStorageFileGetMetadataRecurse(backingStore, parent,
+                                                uid, gid,
+                                                allow_probe, report_broken,
+                                                cycle)) < 0) {
+        if (report_broken)
+            goto cleanup;
+
+        /* if we fail somewhere midway, just accept and return a
+         * broken chain */
+        ret = 0;
+        goto cleanup;
+    }
+
+    src->backingStore = backingStore;
+    backingStore = NULL;
+    ret = 0;
+
+ cleanup:
+    VIR_FREE(buf);
+    virStorageFileDeinit(src);
+    virStorageSourceFree(backingStore);
+    return ret;
+}
+
+
+/**
+ * virStorageFileGetMetadata:
+ *
+ * Extract metadata about the storage volume with the specified
+ * image format. If image format is VIR_STORAGE_FILE_AUTO, it
+ * will probe to automatically identify the format.  Recurses through
+ * the entire chain.
+ *
+ * Open files using UID and GID (or pass -1 for the current user/group).
+ * Treat any backing files without explicit type as raw, unless ALLOW_PROBE.
+ *
+ * Callers are advised never to use VIR_STORAGE_FILE_AUTO as a
+ * format, since a malicious guest can turn a raw file into any
+ * other non-raw format at will.
+ *
+ * If @report_broken is true, the whole function fails with a possibly sane
+ * error instead of just returning a broken chain.
+ *
+ * Caller MUST free result after use via virStorageSourceFree.
+ */
+int
+virStorageFileGetMetadata(virStorageSourcePtr src,
+                          uid_t uid, gid_t gid,
+                          bool allow_probe,
+                          bool report_broken)
+{
+    VIR_DEBUG("path=%s format=%d uid=%u gid=%u probe=%d, report_broken=%d",
+              src->path, src->format, (unsigned int)uid, (unsigned int)gid,
+              allow_probe, report_broken);
+
+    virHashTablePtr cycle = NULL;
+    int ret = -1;
+
+    if (!(cycle = virHashCreate(5, NULL)))
+        return -1;
+
+    if (src->format <= VIR_STORAGE_FILE_NONE)
+        src->format = allow_probe ?
+            VIR_STORAGE_FILE_AUTO : VIR_STORAGE_FILE_RAW;
+
+    ret = virStorageFileGetMetadataRecurse(src, src, uid, gid,
+                                           allow_probe, report_broken, cycle);
+
+    virHashFree(cycle);
+    return ret;
+}
+
+
+/**
+ * virStorageFileGetBackingStoreStr:
+ * @src: storage object
+ *
+ * Extracts the backing store string as stored in the storage volume described
+ * by @src and returns it to the user. Caller is responsible for freeing it.
+ * In case when the string can't be retrieved or does not exist NULL is
+ * returned.
+ */
+char *
+virStorageFileGetBackingStoreStr(virStorageSourcePtr src)
+{
+    virStorageSourcePtr tmp = NULL;
+    char *buf = NULL;
+    ssize_t headerLen;
+    char *ret = NULL;
+
+    /* exit if we can't load information about the current image */
+    if (!virStorageFileSupportsBackingChainTraversal(src))
+        return NULL;
+
+    if (virStorageFileAccess(src, F_OK) < 0)
+        return NULL;
+
+    if ((headerLen = virStorageFileReadHeader(src, VIR_STORAGE_MAX_HEADER,
+                                              &buf)) < 0)
+        return NULL;
+
+    if (!(tmp = virStorageSourceCopy(src, false)))
+        goto cleanup;
+
+    if (virStorageFileGetMetadataInternal(tmp, buf, headerLen, NULL) < 0)
+        goto cleanup;
+
+    VIR_STEAL_PTR(ret, tmp->backingStoreRaw);
+
+ cleanup:
+    VIR_FREE(buf);
+    virStorageSourceFree(tmp);
+
+    return ret;
+}
diff --git a/src/storage/storage_source.h b/src/storage/storage_source.h
new file mode 100644
index 000000000..6b3362244
--- /dev/null
+++ b/src/storage/storage_source.h
@@ -0,0 +1,53 @@
+/*
+ * storage_source.h: Storage source accessors to real storaget
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library.  If not, see
+ * <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __VIR_STORAGE_SOURCE_H__
+# define __VIR_STORAGE_SOURCE_H__
+
+# include <sys/stat.h>
+
+# include "virstoragefile.h"
+
+int virStorageFileInit(virStorageSourcePtr src);
+int virStorageFileInitAs(virStorageSourcePtr src,
+                         uid_t uid, gid_t gid);
+void virStorageFileDeinit(virStorageSourcePtr src);
+
+int virStorageFileCreate(virStorageSourcePtr src);
+int virStorageFileUnlink(virStorageSourcePtr src);
+int virStorageFileStat(virStorageSourcePtr src,
+                       struct stat *stat);
+ssize_t virStorageFileReadHeader(virStorageSourcePtr src,
+                                 ssize_t max_len,
+                                 char **buf);
+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);
+
+int virStorageFileGetMetadata(virStorageSourcePtr src,
+                              uid_t uid, gid_t gid,
+                              bool allow_probe,
+                              bool report_broken)
+    ATTRIBUTE_NONNULL(1);
+
+char *virStorageFileGetBackingStoreStr(virStorageSourcePtr src)
+    ATTRIBUTE_NONNULL(1);
+
+#endif /* __VIR_STORAGE_SOURCE_H__ */
diff --git a/tests/virstoragetest.c b/tests/virstoragetest.c
index a73c53839..d630a213f 100644
--- a/tests/virstoragetest.c
+++ b/tests/virstoragetest.c
@@ -32,6 +32,7 @@
 #include "dirname.h"

 #include "storage/storage_driver.h"
+#include "storage/storage_source.h"

 #define VIR_FROM_THIS VIR_FROM_NONE

-- 
2.12.2


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