From: Peter Krempa <pkrempa@redhat.com>

Refactor qcow2GetExtensions to parse everything at once and directly
assign it into fields in the parsed virStorageSource.

This removes the need for qcow2GetDataFile as it will be parsed
directly.

The patch also simplifies the juggling of variables which was needed to
parse the backing file format filed, when it was passed via pointer in
argument.

qcow2GetExtensions is now invoked on qcow2 images so we can remove the
version check for qcow(v1) images.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
---
 src/storage_file/storage_file_probe.c | 68 +++++----------------------
 1 file changed, 13 insertions(+), 55 deletions(-)

diff --git a/src/storage_file/storage_file_probe.c b/src/storage_file/storage_file_probe.c
index 10e159c27b..73751c7a2f 100644
--- a/src/storage_file/storage_file_probe.c
+++ b/src/storage_file/storage_file_probe.c
@@ -114,7 +114,6 @@ static int
 qcow2GetImageSpecific(virStorageSource *meta,
                       const char *buf,
                       size_t buf_size);
-static int qcow2GetDataFile(char **, virBitmap *, char *, size_t);
 static int
 vmdk4GetImageSpecific(virStorageSource *meta,
                       const char *buf,
@@ -326,7 +325,7 @@ static struct FileTypeInfo const fileTypeInfo[] = {
         qcow2EncryptionInfo,
         NULL,
         NULL,
-        qcow2GetDataFile,
+        NULL,
         NULL,
         qcow2GetImageSpecific
     },
@@ -403,21 +402,16 @@ cowGetImageSpecific(virStorageSource *meta,


 static int
-qcow2GetExtensions(const char *buf,
-                   size_t buf_size,
-                   int *backingFormat,
-                   char **dataFilePath)
+qcow2GetExtensions(virStorageSource *meta,
+                   const char *buf,
+                   size_t buf_size)
 {
     size_t offset;
     size_t extension_start;
     size_t extension_end;
     int version = virReadBufInt32BE(buf + QCOWX_HDR_VERSION);

-    if (version < 2) {
-        /* QCow1 doesn't have the extensions capability
-         * used to store backing format */
-        return 0;
-    }
+    g_clear_pointer(&meta->dataFileRaw, g_free);

     if (version == 2)
         extension_start = QCOW2_HDR_TOTAL_SIZE;
@@ -486,13 +480,7 @@ qcow2GetExtensions(const char *buf,

         switch (magic) {
         case QCOW2_HDR_EXTENSION_BACKING_FORMAT: {
-            g_autofree char *tmp = NULL;
-            if (!backingFormat)
-                break;
-
-            tmp = g_new0(char, len + 1);
-            memcpy(tmp, buf + offset, len);
-            tmp[len] = '\0';
+            g_autofree char *tmp = g_strndup(buf + offset, len);

             /* qemu and qemu-img allow using the protocol driver name inside
              * of the format field in cases when the dummy 'raw' driver should
@@ -500,20 +488,16 @@ qcow2GetExtensions(const char *buf,
              * doesn't look like a format driver name to be a protocol driver
              * directly and thus the image is in fact still considered raw
              */
-            *backingFormat = virStorageFileFormatTypeFromString(tmp);
-            if (*backingFormat <= VIR_STORAGE_FILE_NONE)
-                *backingFormat = VIR_STORAGE_FILE_RAW;
+            meta->backingStoreRawFormat = virStorageFileFormatTypeFromString(tmp);
+            if (meta->backingStoreRawFormat <= VIR_STORAGE_FILE_NONE)
+                meta->backingStoreRawFormat = VIR_STORAGE_FILE_RAW;
             break;
         }

-        case QCOW2_HDR_EXTENSION_DATA_FILE_NAME: {
-            if (!dataFilePath)
-                break;
-
-            *dataFilePath = g_new0(char, len + 1);
-            memcpy(*dataFilePath, buf + offset, len);
+        case QCOW2_HDR_EXTENSION_DATA_FILE_NAME:
+            if (virBitmapIsBitSet(meta->features, VIR_STORAGE_FILE_FEATURE_DATA_FILE))
+                meta->dataFileRaw = g_strndup(buf + offset, len);
             break;
-        }

         case QCOW2_HDR_EXTENSION_END:
             return 0;
@@ -623,8 +607,6 @@ qcow2GetImageSpecific(virStorageSource *meta,
                       const char *buf,
                       size_t buf_size)
 {
-    int format;
-
     meta->clusterSize = 0;
     if (buf_size > (QCOWX_HDR_CLUSTER_BITS_OFFSET + 4)) {
         int clusterBits = virReadBufInt32BE(buf + QCOWX_HDR_CLUSTER_BITS_OFFSET);
@@ -639,33 +621,9 @@ qcow2GetImageSpecific(virStorageSource *meta,
     if (qcow2GetFeatures(meta, buf, buf_size) < 0)
         return -1;

-    format = meta->backingStoreRawFormat;
-
-    if (qcow2GetExtensions(buf, buf_size, &format, NULL) < 0)
+    if (qcow2GetExtensions(meta, buf, buf_size) < 0)
         return 0;

-    meta->backingStoreRawFormat = format;
-
-    return 0;
-}
-
-
-static int
-qcow2GetDataFile(char **res,
-                 virBitmap *features,
-                 char *buf,
-                 size_t buf_size)
-{
-    *res = NULL;
-
-    if (buf_size < QCOW2v3_HDR_FEATURES_INCOMPATIBLE + 8)
-        return 0;
-
-    if (features && virBitmapIsBitSet(features, VIR_STORAGE_FILE_FEATURE_DATA_FILE)) {
-        if (qcow2GetExtensions(buf, buf_size, NULL, res) < 0)
-            return -1;
-    }
-
     return 0;
 }

-- 
2.49.0

On a Thursday in 2025, Peter Krempa via Devel wrote:
>From: Peter Krempa <pkrempa@redhat.com>
>
>Refactor qcow2GetExtensions to parse everything at once and directly
>assign it into fields in the parsed virStorageSource.
>
>This removes the need for qcow2GetDataFile as it will be parsed
>directly.
>
>The patch also simplifies the juggling of variables which was needed to
>parse the backing file format filed, when it was passed via pointer in

extra "filed"?

>argument.
>
>qcow2GetExtensions is now invoked on qcow2 images so we can remove the
>version check for qcow(v1) images.
>
>Signed-off-by: Peter Krempa <pkrempa@redhat.com>
>---
> src/storage_file/storage_file_probe.c | 68 +++++----------------------
> 1 file changed, 13 insertions(+), 55 deletions(-)
>

Reviewed-by: Ján Tomko <jtomko@redhat.com>

Jano