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

[Aurelien Jarno]

On Wed, Apr 08, 2009 at 04:49:05PM +0200, Kevin Wolf wrote:
> 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 <address@hidden>
> ---
>  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
>   */

Actually 0 is never returned, leading to a warning:
  CC    block-vpc.o
block-vpc.c: In function ‘calculate_geometry’:
block-vpc.c:475: warning: control reaches end of non-void function

> -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
> 
> 
> 
> 

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
address@hidden                 http://www.aurel32.net