vmdk: Read footer for streamOptimized images

The footer takes precedence over the header when it exists. It contains
the real grain directory offset that is missing in the header. Without
this patch, streamOptimized images with a footer cannot be read.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Reviewed-by: NJeff Cody <jcody@redhat.com>
(cherry picked from commit 65bd155c)
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

block/vmdk.c

@@ -35,6 +35,7 @@
 #define VMDK4_FLAG_RGD (1 << 1)
 #define VMDK4_FLAG_COMPRESS (1 << 16)
 #define VMDK4_FLAG_MARKER (1 << 17)
+#define VMDK4_GD_AT_END 0xffffffffffffffffULL
 
 typedef struct {
     uint32_t version;
@@ -115,6 +116,13 @@ typedef struct VmdkGrainMarker {
     uint8_t  data[0];
 } VmdkGrainMarker;
 
+enum {
+    MARKER_END_OF_STREAM    = 0,
+    MARKER_GRAIN_TABLE      = 1,
+    MARKER_GRAIN_DIRECTORY  = 2,
+    MARKER_FOOTER           = 3,
+};
+
 static int vmdk_probe(const uint8_t *buf, int buf_size, const char *filename)
 {
     uint32_t magic;
@@ -451,6 +459,54 @@ static int vmdk_open_vmdk4(BlockDriverState *bs,
     if (header.capacity == 0 && header.desc_offset) {
         return vmdk_open_desc_file(bs, flags, header.desc_offset << 9);
     }
+
+    if (le64_to_cpu(header.gd_offset) == VMDK4_GD_AT_END) {
+        /*
+         * The footer takes precedence over the header, so read it in. The
+         * footer starts at offset -1024 from the end: One sector for the
+         * footer, and another one for the end-of-stream marker.
+         */
+        struct {
+            struct {
+                uint64_t val;
+                uint32_t size;
+                uint32_t type;
+                uint8_t pad[512 - 16];
+            } QEMU_PACKED footer_marker;
+
+            uint32_t magic;
+            VMDK4Header header;
+            uint8_t pad[512 - 4 - sizeof(VMDK4Header)];
+
+            struct {
+                uint64_t val;
+                uint32_t size;
+                uint32_t type;
+                uint8_t pad[512 - 16];
+            } QEMU_PACKED eos_marker;
+        } QEMU_PACKED footer;
+
+        ret = bdrv_pread(file,
+            bs->file->total_sectors * 512 - 1536,
+            &footer, sizeof(footer));
+        if (ret < 0) {
+            return ret;
+        }
+
+        /* Some sanity checks for the footer */
+        if (be32_to_cpu(footer.magic) != VMDK4_MAGIC ||
+            le32_to_cpu(footer.footer_marker.size) != 0  ||
+            le32_to_cpu(footer.footer_marker.type) != MARKER_FOOTER ||
+            le64_to_cpu(footer.eos_marker.val) != 0  ||
+            le32_to_cpu(footer.eos_marker.size) != 0  ||
+            le32_to_cpu(footer.eos_marker.type) != MARKER_END_OF_STREAM)
+        {
+            return -EINVAL;
+        }
+
+        header = footer.header;
+    }
+
     l1_entry_sectors = le32_to_cpu(header.num_gtes_per_gte)
                         * le64_to_cpu(header.granularity);
     if (l1_entry_sectors == 0) {