[Qemu-devel] [PATCH 5/7] block/parallels: support padded Parallels images

["Denis V. Lunev" <den@openvz.org>]

Unfortunately, old guest OSes do not align partitions to page size by
default. This is true for Windows 2003 and Windows XP.

For the time being Parallels was created an optimization for such OSes
in its desktop product. Desktop users are not qualified enough to create
properly aligned installations. Thus Parallels makes a blind guess
on a customer behalf and creates so-called "padded" images if guest
OS type is specified as WinXP, Win2k and Win2k3.

"Padding" is a value which should be added to guest LBA to obtain
sector number inside the image. This results in a shifted images.
   0123        offset inside image (in 512 byte sectors)
  +-------
  +.012        guest data (512 byte sectors)
  +-------
The information about this is available in DiskDescriptor.xml ONLY. There
is no such data in the image header.

There share of such images could be evaluated as 6-8% according to the
statistics in my hands.

This patch obtains proper value from XML and applies it on reading.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Acked-by: Roman Kagan <rkagan@parallels.com>
Reviewed-by: Jeff Cody <jcody@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
CC: Stefan Hajnoczi <stefanha@redhat.com>
---
 block/parallels.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/block/parallels.c b/block/parallels.c
index 4a8240d..b27d1ea 100644
--- a/block/parallels.c
+++ b/block/parallels.c
@@ -63,6 +63,7 @@ typedef struct BDRVParallelsState {
     unsigned int tracks;
 
     unsigned int off_multiplier;
+    unsigned int padding;
 } BDRVParallelsState;
 
 
@@ -245,6 +246,7 @@ static int parallels_open_xml(BlockDriverState *bs, int flags, Error **errp)
     const char *data;
     char image_path[PATH_MAX];
     Error *local_err = NULL;
+    BDRVParallelsState *s = bs->opaque;
 
     ret = size = bdrv_getlength(bs->file);
     if (ret < 0) {
@@ -274,6 +276,19 @@ static int parallels_open_xml(BlockDriverState *bs, int flags, Error **errp)
     if (root == NULL) {
         goto fail;
     }
+
+    data = xml_get_text(root, "Disk_Parameters", "Padding", NULL);
+    if (data != NULL) {
+        char *endptr;
+        unsigned long pad;
+
+        pad = strtoul(data, &endptr, 0);
+        if ((endptr != NULL && *endptr != '\0') || pad > UINT_MAX) {
+            goto fail;
+        }
+        s->padding = (uint32_t)pad;
+    }
+
     image = xml_seek(root, "StorageData", "Storage", "Image", NULL);
     data = ""; /* make gcc happy */
     for (size = 0; image != NULL; image = image->next) {
@@ -375,6 +390,10 @@ static int64_t seek_to_sector(BlockDriverState *bs, int64_t sector_num)
 static int parallels_read(BlockDriverState *bs, int64_t sector_num,
                     uint8_t *buf, int nb_sectors)
 {
+    BDRVParallelsState *s = bs->opaque;
+
+    sector_num += s->padding;
+
     while (nb_sectors > 0) {
         int64_t position = seek_to_sector(bs, sector_num);
         if (position >= 0) {
-- 
1.9.1