Re: [Qemu-devel] [PATCH] allow reading variable size vmdk descriptor files

[Don Slutz]

On 06/12/13 03:08, Evgeny Budilovsky wrote:
The hard-coded 2k buffer on the stack won't allow reading big descriptor
files which can be generated when storing big images (For example 500G
vmdk splitted to 2G chunks).
Signed-off-by: Evgeny Budilovsky <evgeny.budilov...@ravellosystems.com>
---
  block/vmdk.c |   28 +++++++++++++++++++++-------
  1 file changed, 21 insertions(+), 7 deletions(-)

diff --git a/block/vmdk.c b/block/vmdk.c
index 608daaf..1bc944b 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -719,27 +719,41 @@ static int vmdk_open_desc_file(BlockDriverState *bs, int 
flags,
                                 int64_t desc_offset)
  {
      int ret;
-    char buf[2048];
+    char *buf = NULL;
      char ct[128];
      BDRVVmdkState *s = bs->opaque;
+    int64_t size;

-    ret = bdrv_pread(bs->file, desc_offset, buf, sizeof(buf));
+    size = bdrv_get_allocated_file_size(bs);
+    if (size < 0) {
+        return -EINVAL;
+    }
+
While this is right for vmdk splitted to 2G chunks, I think this will 
fail for a big enough "monolithicFlat" vmdk where there is only the 1 
file (g_malloc() will most likely fail for a 500GB file).
+    buf = g_malloc0(size+1);
+
+    ret = bdrv_pread(bs->file, desc_offset, buf, size);
      if (ret < 0) {
-        return ret;
+        goto exit;
      }
-    buf[2047] = '\0';
      if (vmdk_parse_description(buf, "createType", ct, sizeof(ct))) {
-        return -EMEDIUMTYPE;
+        ret = -EMEDIUMTYPE;
+        goto exit;
      }
      if (strcmp(ct, "monolithicFlat") &&
          strcmp(ct, "twoGbMaxExtentSparse") &&
          strcmp(ct, "twoGbMaxExtentFlat")) {
          fprintf(stderr,
                  "VMDK: Not supported image type \"%s\""".\n", ct);
-        return -ENOTSUP;
+        ret = -ENOTSUP;
+        goto exit;
      }
      s->desc_offset = 0;
-    return vmdk_parse_extents(buf, bs, bs->file->filename);
+    ret = vmdk_parse_extents(buf, bs, bs->file->filename);
+exit:
+    if (buf) {
+        g_free(buf);
+    }
+    return ret;
  }

  static int vmdk_open(BlockDriverState *bs, QDict *options, int flags)
--
1.7.9.5

   -Don Slutz