[libvirt] [PATCH 2/2] Support for probing qed image metadata

[Adam Litke]

Implement getBackingStore() for QED images.  The header format is defined in
the QED spec: http://wiki.qemu.org/Features/QED .

Signed-off-by: Adam Litke <agl at us.ibm.com>
Cc: Stefan Hajnoczi <stefan.hajnoczi at uk.ibm.com>
Cc: Anthony Liguori <aliguori at linux.vnet.ibm.com>
---
 src/util/storage_file.c |   78 ++++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 77 insertions(+), 1 deletions(-)

diff --git a/src/util/storage_file.c b/src/util/storage_file.c
index 6e099ed..51ee0c8 100644
--- a/src/util/storage_file.c
+++ b/src/util/storage_file.c
@@ -89,6 +89,8 @@ static int qcow2GetBackingStore(char **, int *,
                                 const unsigned char *, size_t);
 static int vmdk4GetBackingStore(char **, int *,
                                 const unsigned char *, size_t);
+static int
+qedGetBackingStore(char **, int *, const unsigned char *, size_t);
 
 #define QCOWX_HDR_VERSION (4)
 #define QCOWX_HDR_BACKING_FILE_OFFSET (QCOWX_HDR_VERSION+4)
@@ -105,6 +107,11 @@ static int vmdk4GetBackingStore(char **, int *,
 #define QCOW2_HDR_EXTENSION_BACKING_FORMAT 0xE2792ACA
 
 #define QED_HDR_IMAGE_SIZE 40
+#define QED_HDR_FEATURES_OFFSET 16
+#define QED_HDR_BACKING_FILE_OFFSET 56
+#define QED_HDR_BACKING_FILE_SIZE 60
+#define QED_F_BACKING_FILE 0x01
+#define QED_F_BACKING_FORMAT_NO_PROBE 0x04
 
 /* VMDK needs at least this to find backing store,
  * other formats need less */
@@ -156,7 +163,7 @@ static struct FileTypeInfo const fileTypeInfo[] = {
     [VIR_STORAGE_FILE_QED] = {
         "QED\0", NULL,
         LV_LITTLE_ENDIAN, -1, -1,
-        QED_HDR_IMAGE_SIZE, 8, 1, -1, NULL,
+        QED_HDR_IMAGE_SIZE, 8, 1, -1, qedGetBackingStore,
     },
     [VIR_STORAGE_FILE_VMDK] = {
         "KDMV", NULL,
@@ -416,6 +423,75 @@ cleanup:
     return ret;
 }
 
+static unsigned long
+qedGetHeaderUL(const unsigned char *loc)
+{
+    return ( ((unsigned long)loc[3] << 24)
+           | ((unsigned long)loc[2] << 16)
+           | ((unsigned long)loc[1] << 8)
+           | ((unsigned long)loc[0] << 0));
+}
+
+static unsigned long long
+qedGetHeaderULL(const unsigned char *loc)
+{
+    return ( ((unsigned long)loc[7] << 56)
+           | ((unsigned long)loc[6] << 48)
+           | ((unsigned long)loc[5] << 40)
+           | ((unsigned long)loc[4] << 32)
+           | ((unsigned long)loc[3] << 24)
+           | ((unsigned long)loc[2] << 16)
+           | ((unsigned long)loc[1] << 8)
+           | ((unsigned long)loc[0] << 0));
+}
+
+static int
+qedGetBackingStore(char **res,
+                   int *format,
+                   const unsigned char *buf,
+                   size_t buf_size)
+{
+    unsigned long long flags;
+    unsigned long offset, size;
+
+    *res = NULL;
+    /* Check if this image has a backing file */
+    if (buf_size < QED_HDR_FEATURES_OFFSET+8)
+        return BACKING_STORE_INVALID;
+    flags = qedGetHeaderULL(buf + QED_HDR_FEATURES_OFFSET);
+    if (!(flags & QED_F_BACKING_FILE))
+        return BACKING_STORE_OK;
+
+    /* Parse the backing file */
+    if (buf_size < QED_HDR_BACKING_FILE_OFFSET+8)
+        return BACKING_STORE_INVALID;
+    offset = qedGetHeaderUL(buf + QED_HDR_BACKING_FILE_OFFSET);
+    if (offset > buf_size)
+        return BACKING_STORE_INVALID;
+    size = qedGetHeaderUL(buf + QED_HDR_BACKING_FILE_SIZE);
+    if (size == 0)
+        return BACKING_STORE_OK;
+    if (offset + size > buf_size || offset + size < offset)
+        return BACKING_STORE_INVALID;
+    if (size + 1 == 0)
+        return BACKING_STORE_INVALID;
+    if (VIR_ALLOC_N(*res, size + 1) < 0) {
+        virReportOOMError();
+        return BACKING_STORE_ERROR;
+    }
+    memcpy(*res, buf + offset, size);
+    (*res)[size] = '\0';
+
+    if (format) {
+        if (flags & QED_F_BACKING_FORMAT_NO_PROBE)
+            *format = virStorageFileFormatTypeFromString("raw");
+        else
+            *format = VIR_STORAGE_FILE_AUTO;
+    }
+
+    return BACKING_STORE_OK;
+}
+
 /**
  * Return an absolute path corresponding to PATH, which is absolute or relative
  * to the directory containing BASE_FILE, or NULL on error
-- 
1.7.3.2.164.g6f10c