Re: [PATCH] qemu-img: add seek and -n option to dd command

[David Edmondson]

On Thursday, 2021-01-28 at 15:07:04 +01, Peter Lieven wrote:

> Signed-off-by: Peter Lieven <pl@kamp.de>
>
> diff --git a/docs/tools/qemu-img.rst b/docs/tools/qemu-img.rst
> index b615aa8419..7d4564c2b8 100644
> --- a/docs/tools/qemu-img.rst
> +++ b/docs/tools/qemu-img.rst
> @@ -209,6 +209,10 @@ Parameters to dd subcommand:
>  
>  .. program:: qemu-img-dd
>  
> +.. option:: -n
> +
> +  Skip the creation of the output file
> +
>  .. option:: bs=BLOCK_SIZE
>  
>    Defines the block size
> @@ -229,6 +233,10 @@ Parameters to dd subcommand:
>  
>    Sets the number of input blocks to skip
>  
> +.. option:: sseek=BLOCKS
> +
> +  Sets the number of blocks to seek into the output
> +
>  Parameters to snapshot subcommand:
>  
>  .. program:: qemu-img-snapshot
> diff --git a/qemu-img.c b/qemu-img.c
> index 8597d069af..d7f390e382 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -213,12 +213,17 @@ static void QEMU_NORETURN help(void)
>             "  '-s' run in Strict mode - fail on different image size or 
> sector allocation\n"
>             "\n"
>             "Parameters to dd subcommand:\n"
> +           "  '-n' skips the target volume creation (useful if the volume is 
> created\n"
> +           "       prior to running qemu-img). Note that he behaviour is not 
> identical to\n"

s/he/the/

> +           "       original dd option conv=nocreat. The output is neither 
> truncated nor\n"
> +           "       is it possible to write past the end of an existing 
> file.\n"
>             "  'bs=BYTES' read and write up to BYTES bytes at a time "
>             "(default: 512)\n"
>             "  'count=N' copy only N input blocks\n"
>             "  'if=FILE' read from FILE\n"
>             "  'of=FILE' write to FILE\n"
> -           "  'skip=N' skip N bs-sized blocks at the start of input\n";
> +           "  'skip=N' skip N bs-sized blocks at the start of input\n"
> +           "  'seek=N' seek N bs-sized blocks into the output\n";
>  
>      printf("%s\nSupported formats:", help_msg);
>      bdrv_iterate_format(format_print, NULL, false);
> @@ -4885,6 +4890,7 @@ static int img_bitmap(int argc, char **argv)
>  #define C_IF      04
>  #define C_OF      010
>  #define C_SKIP    020
> +#define C_SEEK    040
>  
>  struct DdInfo {
>      unsigned int flags;
> @@ -4964,6 +4970,19 @@ static int img_dd_skip(const char *arg,
>      return 0;
>  }
>  
> +static int img_dd_seek(const char *arg,
> +                       struct DdIo *in, struct DdIo *out,
> +                       struct DdInfo *dd)
> +{
> +    out->offset = cvtnum("seek", arg);
> +
> +    if (in->offset < 0) {
> +        return 1;
> +    }
> +
> +    return 0;
> +}
> +
>  static int img_dd(int argc, char **argv)
>  {
>      int ret = 0;
> @@ -4980,7 +4999,7 @@ static int img_dd(int argc, char **argv)
>      const char *fmt = NULL;
>      int64_t size = 0;
>      int64_t block_count = 0, out_pos, in_pos;
> -    bool force_share = false;
> +    bool force_share = false, skip_create = false;
>      struct DdInfo dd = {
>          .flags = 0,
>          .count = 0,
> @@ -5004,6 +5023,7 @@ static int img_dd(int argc, char **argv)
>          { "if", img_dd_if, C_IF },
>          { "of", img_dd_of, C_OF },
>          { "skip", img_dd_skip, C_SKIP },
> +        { "seek", img_dd_seek, C_SEEK },
>          { NULL, NULL, 0 }
>      };
>      const struct option long_options[] = {
> @@ -5014,7 +5034,7 @@ static int img_dd(int argc, char **argv)
>          { 0, 0, 0, 0 }
>      };
>  
> -    while ((c = getopt_long(argc, argv, ":hf:O:U", long_options, NULL))) {
> +    while ((c = getopt_long(argc, argv, ":hf:O:Un", long_options, NULL))) {
>          if (c == EOF) {
>              break;
>          }
> @@ -5037,6 +5057,9 @@ static int img_dd(int argc, char **argv)
>          case 'U':
>              force_share = true;
>              break;
> +        case 'n':
> +            skip_create = true;
> +            break;
>          case OPTION_OBJECT:
>              if (!qemu_opts_parse_noisily(&qemu_object_opts, optarg, true)) {
>                  ret = -1;
> @@ -5116,22 +5139,25 @@ static int img_dd(int argc, char **argv)
>          ret = -1;
>          goto out;
>      }
> -    if (!drv->create_opts) {
> -        error_report("Format driver '%s' does not support image creation",
> -                     drv->format_name);
> -        ret = -1;
> -        goto out;
> -    }
> -    if (!proto_drv->create_opts) {
> -        error_report("Protocol driver '%s' does not support image creation",
> -                     proto_drv->format_name);
> -        ret = -1;
> -        goto out;
> -    }
> -    create_opts = qemu_opts_append(create_opts, drv->create_opts);
> -    create_opts = qemu_opts_append(create_opts, proto_drv->create_opts);
>  
> -    opts = qemu_opts_create(create_opts, NULL, 0, &error_abort);
> +    if (!skip_create) {
> +        if (!drv->create_opts) {
> +            error_report("Format driver '%s' does not support image 
> creation",
> +                         drv->format_name);
> +            ret = -1;
> +            goto out;
> +        }
> +        if (!proto_drv->create_opts) {
> +            error_report("Protocol driver '%s' does not support image 
> creation",
> +                         proto_drv->format_name);
> +            ret = -1;
> +            goto out;
> +        }
> +        create_opts = qemu_opts_append(create_opts, drv->create_opts);
> +        create_opts = qemu_opts_append(create_opts, proto_drv->create_opts);
> +
> +        opts = qemu_opts_create(create_opts, NULL, 0, &error_abort);
> +    }
>  
>      size = blk_getlength(blk1);
>      if (size < 0) {
> @@ -5145,22 +5171,25 @@ static int img_dd(int argc, char **argv)
>          size = dd.count * in.bsz;
>      }
>  
> -    /* Overflow means the specified offset is beyond input image's size */
> -    if (dd.flags & C_SKIP && (in.offset > INT64_MAX / in.bsz ||
> -                              size < in.bsz * in.offset)) {
> -        qemu_opt_set_number(opts, BLOCK_OPT_SIZE, 0, &error_abort);
> -    } else {
> -        qemu_opt_set_number(opts, BLOCK_OPT_SIZE,
> -                            size - in.bsz * in.offset, &error_abort);
> -    }
> +    if (!skip_create) {
> +        /* Overflow means the specified offset is beyond input image's size 
> */
> +        if (dd.flags & C_SKIP && (in.offset > INT64_MAX / in.bsz ||
> +                                  size < in.bsz * in.offset)) {
> +            qemu_opt_set_number(opts, BLOCK_OPT_SIZE, 0, &error_abort);
> +        } else {
> +            qemu_opt_set_number(opts, BLOCK_OPT_SIZE,
> +                                out.bsz * out.offset + size -
> +                                in.bsz * in.offset, &error_abort);
> +        }
>  
> -    ret = bdrv_create(drv, out.filename, opts, &local_err);
> -    if (ret < 0) {
> -        error_reportf_err(local_err,
> -                          "%s: error while creating output image: ",
> -                          out.filename);
> -        ret = -1;
> -        goto out;
> +        ret = bdrv_create(drv, out.filename, opts, &local_err);
> +        if (ret < 0) {
> +            error_reportf_err(local_err,
> +                              "%s: error while creating output image: ",
> +                              out.filename);
> +            ret = -1;
> +            goto out;
> +        }
>      }
>  
>      /* TODO, we can't honour --image-opts for the target,
> @@ -5189,7 +5218,7 @@ static int img_dd(int argc, char **argv)
>  
>      in.buf = g_new(uint8_t, in.bsz);
>  
> -    for (out_pos = 0; in_pos < size; block_count++) {
> +    for (out_pos = out.offset * out.bsz; in_pos < size; block_count++) {
>          int in_ret, out_ret;
>  
>          if (in_pos + in.bsz > size) {
> -- 
> 2.17.1

dme.
-- 
But they'll laugh at you in Jackson, and I'll be dancin' on a Pony Keg.