[libvirt] [PATCH 1/5] conf: provide details on network backing store

[Eric Blake]

So far, my work has been merely preserving the status quo of
backing file analysis.  But this patch starts to tread in the
territory of making the backing chain code more powerful - we
will eventually support network storage containing non-raw
formats.  Here, we expose metadata information about a network
backing store, even if that information is still hardcoded to
a raw format for now.

* src/util/virstoragefile.c (virStorageFileGetMetadataRecurse):
Also populate struct for non-file backing.
(virStorageFileGetMetadata, virStorageFileGetMetadatainternal):
Recognize non-file top image.
(virFindBackingFile): Add comment.
* tests/virstoragetest.c (mymain): Update test to reflect it.

Signed-off-by: Eric Blake <eblake at redhat.com>
---
 src/util/virstoragefile.c | 62 +++++++++++++++++++++++++++++++++++------------
 tests/virstoragetest.c    | 17 +++++++++----
 2 files changed, 59 insertions(+), 20 deletions(-)

diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c
index f5fe8ad..7a91a01 100644
--- a/src/util/virstoragefile.c
+++ b/src/util/virstoragefile.c
@@ -569,6 +569,14 @@ static int ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2) ATTRIBUTE_NONNULL(4)
 virFindBackingFile(const char *start, const char *path,
                    char **directory, char **canonical)
 {
+    /* FIXME - when we eventually allow non-raw network devices, we
+     * must ensure that we handle backing files the same way as qemu.
+     * For a qcow2 top file of gluster://server/vol/img, qemu treats
+     * the relative backing file 'rel' as meaning
+     * 'gluster://server/vol/rel', while the backing file '/abs' is
+     * used as a local file.  But we cannot canonicalize network
+     * devices via canonicalize_file_name(), because they are not part
+     * of the local file system.  */
     char *combined = NULL;
     int ret = -1;

@@ -874,6 +882,12 @@ virStorageFileGetMetadataInternal(const char *path,
                              meta->backingStoreRaw, path);

                 }
+            } else {
+                if (VIR_STRDUP(meta->backingStoreRaw, backing) < 0) {
+                    VIR_FREE(backing);
+                    goto cleanup;
+                }
+                backingFormat = VIR_STORAGE_FILE_RAW;
             }
             VIR_FREE(backing);
             meta->backingStoreFormat = backingFormat;
@@ -1132,18 +1146,32 @@ virStorageFileGetMetadataRecurse(const char *path, const char *canonPath,
     if (virHashAddEntry(cycle, canonPath, (void *)1) < 0)
         return -1;

-    if ((fd = virFileOpenAs(canonPath, O_RDONLY, 0, uid, gid, 0)) < 0) {
-        virReportSystemError(-fd, _("Failed to open file '%s'"), path);
-        return -1;
-    }
+    if (virBackingStoreIsFile(path)) {
+        if ((fd = virFileOpenAs(canonPath, O_RDONLY, 0, uid, gid, 0)) < 0) {
+            virReportSystemError(-fd, _("Failed to open file '%s'"), path);
+            return -1;
+        }

-    ret = virStorageFileGetMetadataFromFDInternal(path, canonPath, directory,
-                                                  fd, format, meta);
+        ret = virStorageFileGetMetadataFromFDInternal(path, canonPath,
+                                                      directory,
+                                                      fd, format, meta);

-    if (VIR_CLOSE(fd) < 0)
-        VIR_WARN("could not close file %s", path);
+        if (VIR_CLOSE(fd) < 0)
+            VIR_WARN("could not close file %s", path);
+    } else {
+        /* FIXME: when the proper storage drivers are compiled in, it
+         * would be nice to read metadata from the network storage to
+         * allow for non-raw images.  */
+        if (VIR_STRDUP(meta->path, path) < 0)
+            return -1;
+        if (VIR_STRDUP(meta->canonPath, path) < 0)
+            return -1;
+        meta->type = VIR_STORAGE_TYPE_NETWORK;
+        meta->format = VIR_STORAGE_FILE_RAW;
+        ret = 0;
+    }

-    if (ret == 0 && meta->backingStoreIsFile) {
+    if (ret == 0 && meta->backingStore) {
         virStorageFileMetadataPtr backing;

         if (meta->backingStoreFormat == VIR_STORAGE_FILE_AUTO && !allow_probe)
@@ -1207,12 +1235,16 @@ virStorageFileGetMetadata(const char *path, int format,
     if (!cycle)
         return NULL;

-    if (!(canonPath = canonicalize_file_name(path))) {
-        virReportSystemError(errno, _("unable to resolve '%s'"), path);
-        goto cleanup;
-    }
-    if (!(directory = mdir_name(path))) {
-        virReportOOMError();
+    if (virBackingStoreIsFile(path)) {
+        if (!(canonPath = canonicalize_file_name(path))) {
+            virReportSystemError(errno, _("unable to resolve '%s'"), path);
+            goto cleanup;
+        }
+        if (!(directory = mdir_name(path))) {
+            virReportOOMError();
+            goto cleanup;
+        }
+    } else if (VIR_STRDUP(canonPath, path) < 0) {
         goto cleanup;
     }
     if (VIR_ALLOC(meta) < 0)
diff --git a/tests/virstoragetest.c b/tests/virstoragetest.c
index 9a9b0d8..e8409f6 100644
--- a/tests/virstoragetest.c
+++ b/tests/virstoragetest.c
@@ -621,17 +621,24 @@ mymain(void)
     if (virCommandRun(cmd, NULL) < 0)
         ret = -1;
     qcow2.expBackingStore = "nbd:example.org:6000";
-    qcow2.expBackingStoreRaw = NULL;
+    qcow2.expBackingStoreRaw = "nbd:example.org:6000";
     qcow2.expBackingDirRel = NULL;
     qcow2.expBackingDirAbs = NULL;
     qcow2.expBackingFormat = VIR_STORAGE_FILE_RAW;

     /* Qcow2 file with backing protocol instead of file */
+    testFileData nbd = {
+        .pathRel = "nbd:example.org:6000",
+        .pathAbs = "nbd:example.org:6000",
+        .canonPath = "nbd:example.org:6000",
+        .type = VIR_STORAGE_TYPE_NETWORK,
+        .format = VIR_STORAGE_FILE_RAW,
+    };
     TEST_CHAIN(11, "qcow2", absqcow2, VIR_STORAGE_FILE_QCOW2,
-               (&qcow2), EXP_PASS,
-               (&qcow2), ALLOW_PROBE | EXP_PASS,
-               (&qcow2), EXP_PASS,
-               (&qcow2), ALLOW_PROBE | EXP_PASS);
+               (&qcow2, &nbd), EXP_PASS,
+               (&qcow2, &nbd), ALLOW_PROBE | EXP_PASS,
+               (&qcow2, &nbd), EXP_PASS,
+               (&qcow2, &nbd), ALLOW_PROBE | EXP_PASS);

     /* qed file */
     testFileData qed = {
-- 
1.9.0