Re: [Qemu-devel] [PATCH] qemu-img: adding a "-F base_fmt" option to "qemu-img create -b"

[Anthony Liguori]

address@hidden wrote:
> From: Uri Lublin <address@hidden>
>
> If the user specifies the backing file format,
> then when opening the backing file, there is no need
> to probe the (backing file) image to figure out its format.
>
> This follows my previous patch implementing fmt:FMT: prefix for backing
> filename.
>   

But how does this work in the absence of supporting fmt:FMT?  Does this 
imply that the other patch is needed too?

Regards,

Anthony Liguori

> Suggested by Daniel P. Berrange.
>
> Signed-off-by: Uri Lublin <address@hidden>
> ---
>  qemu-img.c    |   31 ++++++++++++++++++++++++++++---
>  qemu-img.texi |    4 +++-
>  2 files changed, 31 insertions(+), 4 deletions(-)
>
> diff --git a/qemu-img.c b/qemu-img.c
> index 964b28b..02c513f 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -25,6 +25,7 @@
>  #include "osdep.h"
>  #include "block_int.h"
>  #include <assert.h>
> +#include <stdio.h>
>  
>  #ifdef _WIN32
>  #define WIN32_LEAN_AND_MEAN
> @@ -57,7 +58,7 @@ static void help(void)
>             "QEMU disk image utility\n"
>             "\n"
>             "Command syntax:\n"
> -           "  create [-e] [-6] [-b base_image] [-f fmt] filename [size]\n"
> +           "  create [-e] [-6] [-F fmt] [-b base_image] [-f fmt] filename 
> [size]\n"
>             "  commit [-f fmt] filename\n"
>             "  convert [-c] [-e] [-6] [-f fmt] [-O output_fmt] [-B 
> output_base_image] filename [filename2 [...]] output_filename\n"
>             "  info [-f fmt] filename\n"
> @@ -215,21 +216,26 @@ static int img_create(int argc, char **argv)
>  {
>      int c, ret, flags;
>      const char *fmt = "raw";
> +    const char *base_fmt = NULL;
>      const char *filename;
>      const char *base_filename = NULL;
>      uint64_t size;
>      const char *p;
>      BlockDriver *drv;
> +    char filename_buff[1024];
>  
>      flags = 0;
>      for(;;) {
> -        c = getopt(argc, argv, "b:f:he6");
> +        c = getopt(argc, argv, "F:b:f:he6");
>          if (c == -1)
>              break;
>          switch(c) {
>          case 'h':
>              help();
>              break;
> +        case 'F':
> +            base_fmt = optarg;
> +            break;
>          case 'b':
>              base_filename = optarg;
>              break;
> @@ -250,7 +256,15 @@ static int img_create(int argc, char **argv)
>      size = 0;
>      if (base_filename) {
>          BlockDriverState *bs;
> -        bs = bdrv_new_open(base_filename, NULL);
> +        BlockDriver *base_drv = NULL;
> +        
> +        if (base_fmt) {
> +            base_drv = bdrv_find_format(base_fmt);
> +            if (base_drv == NULL)
> +                error("Unknown basefile format '%s'", base_fmt);
> +        }
> +        
> +        bs = bdrv_new_open(base_filename, base_fmt);
>          bdrv_get_geometry(bs, &size);
>          size *= 512;
>          bdrv_delete(bs);
> @@ -281,8 +295,19 @@ static int img_create(int argc, char **argv)
>      if (base_filename) {
>          printf(", backing_file=%s",
>                 base_filename);
> +        if (base_fmt)
> +            printf(", backing_fmt=%s",
> +                   base_fmt);
>      }
>      printf(", size=%" PRIu64 " kB\n", size / 1024);
> +    if (base_filename && base_fmt) {
> +        int len;
> +        len = snprintf(filename_buff, sizeof(filename_buff), "fmt:%s:%s", 
> +                       base_fmt, base_filename);
> +        if (len < 0)
> +            error("internal failure: snprintf failed");
> +        base_filename = filename_buff;
> +    }
>      ret = bdrv_create(drv, filename, size / 512, base_filename, flags);
>      if (ret < 0) {
>          if (ret == -ENOTSUP) {
> diff --git a/qemu-img.texi b/qemu-img.texi
> index 1c0504b..eaeaf07 100644
> --- a/qemu-img.texi
> +++ b/qemu-img.texi
> @@ -8,7 +8,7 @@ usage: qemu-img command [command options]
>  
>  The following commands are supported:
>  @table @option
> address@hidden create [-e] [-6] [-b @var{base_image}] [-f @var{fmt}] 
> @var{filename} address@hidden
> address@hidden create [-e] [-6] [-F @var{base_fmt}] [-b @var{base_image}] [-f 
> @var{fmt}] @var{filename} address@hidden
>  @item commit [-f @var{fmt}] @var{filename}
>  @item convert [-c] [-e] [-6] [-f @var{fmt}] [-O @var{output_fmt}] [-B 
> @var{output_base_image}] @var{filename} address@hidden [...]] 
> @var{output_filename}
>  @item info [-f @var{fmt}] @var{filename}
> @@ -26,6 +26,8 @@ forces the output image to be created as a copy on write
>  image of the specified base image; @code{output_base_image} should have the 
> same
>  content as the input's base image, however the path, image format, etc may
>  differ
> address@hidden base_fmt
> +is the disk image format of @var{base_image}. for more information look at 
> @var{fmt}
>  @item fmt
>  is the disk image format. It is guessed automatically in most cases. The 
> following formats are supported:
>  
>