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Re: [Qemu-devel] [PATCH 2/5] Support human unit formats in strtobytes, e


From: Markus Armbruster
Subject: Re: [Qemu-devel] [PATCH 2/5] Support human unit formats in strtobytes, eg. 1.0G
Date: Tue, 28 Sep 2010 11:56:41 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux)

address@hidden writes:

> From: Jes Sorensen <address@hidden>
>
> Signed-off-by: Jes Sorensen <address@hidden>
> ---
>  cutils.c |   34 ++++++++++++++++++++++++++--------
>  1 files changed, 26 insertions(+), 8 deletions(-)
>
> diff --git a/cutils.c b/cutils.c
> index dabbed4..67767a9 100644
> --- a/cutils.c
> +++ b/cutils.c
> @@ -259,34 +259,52 @@ int fcntl_setfl(int fd, int flag)
>   */
>  uint64_t strtobytes(const char *nptr, char **end)
>  {
> -    uint64_t value;
> +    uint64_t retval = 0;
>      char *endptr;
> +    int mul_required = 0;
> +    double val, mul = 1;
> +
> +    endptr = (char *)nptr + strspn(nptr, " 0123456789");
> +    if (*endptr == '.') {
> +        mul_required = 1;
> +    }
> +
> +    val = strtod(nptr, &endptr);
> +
> +    if (val < 0)
> +        goto fail;

I pointed out several problems with the use of strtoull() in PATCH 1/5,
and now you go ahead and switch over to strtod() in PATCH 2/5.  Gee,
thanks!  For penance, I want you to peruse strtod(3) and figure out its
correct usage ;)

>  
> -    value = strtoll(nptr, &endptr, 0);
>      switch (*endptr++) {
>      case 'K':
>      case 'k':
> -        value <<= 10;
> +        mul = 1 << 10;
>          break;
>      case 0:
> +    case ' ':
> +        if (mul_required) {
> +            goto fail;
> +        }

I wouldn't have bothered catching this case.  Instead, I'd have checked
that the final conversion to uint64_t is exact.  But since you coded it
already, feel free to keep it.

>      case 'M':
>      case 'm':
> -        value <<= 20;
> +        mul = 1ULL << 20;
>          break;
>      case 'G':
>      case 'g':
> -        value <<= 30;
> +        mul = 1ULL << 30;
>          break;
>      case 'T':
>      case 't':
> -        value <<= 40;
> +        mul = 1ULL << 40;
>          break;
>      default:
> -        value = 0;
> +        goto fail;
>      }
>  
> +    retval = (uint64_t)(val * mul);
> +

What if the conversion overflows uint64_t?  Shouldn't we catch that?

>      if (end)
>          *end = endptr;
>  
> -    return value;
> +fail:
> +    return retval;
>  }




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