[Qemu-devel] [PATCH] block-vpc: Don't silently create smaller image than requested

[Kevin Wolf <kwolf@redhat.com>]

The algorithm from the VHD specification for CHS calculation silently limits
images to 127 GB which may confuse a user who requested a larger image. Better
output an error message and abort.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block-vpc.c |    9 ++++++---
 qemu-img.c  |    4 ++++
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/block-vpc.c b/block-vpc.c
index 7ae5202..d915d20 100644
--- a/block-vpc.c
+++ b/block-vpc.c
@@ -433,14 +433,16 @@ static int vpc_write(BlockDriverState *bs, int64_t sector_num,
  *
  * Note that the geometry doesn't always exactly match total_sectors but
  * may round it down.
+ *
+ * Returns 0 on success, -EFBIG if the size is larger than 127 GB
  */
-static void calculate_geometry(int64_t total_sectors, uint16_t* cyls,
+static int calculate_geometry(int64_t total_sectors, uint16_t* cyls,
     uint8_t* heads, uint8_t* secs_per_cyl)
 {
     uint32_t cyls_times_heads;
 
     if (total_sectors > 65535 * 16 * 255)
-        total_sectors = 65535 * 16 * 255;
+        return -EFBIG;
 
     if (total_sectors > 65535 * 16 * 63) {
         *secs_per_cyl = 255;
@@ -493,7 +495,8 @@ static int vpc_create(const char *filename, int64_t total_sectors,
         return -EIO;
 
     // Calculate matching total_size and geometry
-    calculate_geometry(total_sectors, &cyls, &heads, &secs_per_cyl);
+    if (calculate_geometry(total_sectors, &cyls, &heads, &secs_per_cyl))
+        return -EFBIG;
     total_sectors = (int64_t) cyls * heads * secs_per_cyl;
 
     // Prepare the Hard Disk Footer
diff --git a/qemu-img.c b/qemu-img.c
index 913ad34..ccf4a6f 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -306,6 +306,8 @@ static int img_create(int argc, char **argv)
     if (ret < 0) {
         if (ret == -ENOTSUP) {
             error("Formatting or formatting option not supported for file format '%s'", fmt);
+        } else if (ret == -EFBIG) {
+            error("The image size is too large for file format '%s'", fmt);
         } else {
             error("Error while formatting");
         }
@@ -494,6 +496,8 @@ static int img_convert(int argc, char **argv)
     if (ret < 0) {
         if (ret == -ENOTSUP) {
             error("Formatting not supported for file format '%s'", out_fmt);
+        } else if (ret == -EFBIG) {
+            error("The image size is too large for file format '%s'", out_fmt);
         } else {
             error("Error while formatting '%s'", out_filename);
         }
-- 
1.6.0.6