[Qemu-devel] Re: [PATCH v2 2/7] cutils: Add bytes_to_str() to format byte values

[Avi Kivity <avi@redhat.com>]

  On 10/08/2010 05:48 PM, Stefan Hajnoczi wrote:
> From: Anthony Liguori<aliguori@us.ibm.com>
>
> This common function converts byte counts to human-readable strings with
> proper units.
>
> Signed-off-by: Anthony Liguori<aliguori@us.ibm.com>
> Signed-off-by: Stefan Hajnoczi<stefanha@linux.vnet.ibm.com>
> ---
>   cutils.c      |   15 +++++++++++++++
>   qemu-common.h |    1 +
>   2 files changed, 16 insertions(+), 0 deletions(-)
>
> diff --git a/cutils.c b/cutils.c
> index 6c32198..5041203 100644
> --- a/cutils.c
> +++ b/cutils.c
> @@ -301,3 +301,18 @@ int get_bits_from_size(size_t size)
>       return __builtin_ctzl(size);
>   #endif
>   }
> +
> +void bytes_to_str(char *buffer, size_t buffer_len, uint64_t size)
> +{
> +    if (size<  (1ULL<<  10)) {
> +        snprintf(buffer, buffer_len, "%" PRIu64 " byte(s)", size);
> +    } else if (size<  (1ULL<<  20)) {
> +        snprintf(buffer, buffer_len, "%" PRIu64 " KB(s)", size>>  10);
> +    } else if (size<  (1ULL<<  30)) {
> +        snprintf(buffer, buffer_len, "%" PRIu64 " MB(s)", size>>  20);
> +    } else if (size<  (1ULL<<  40)) {
> +        snprintf(buffer, buffer_len, "%" PRIu64 " GB(s)", size>>  30);
> +    } else {
> +        snprintf(buffer, buffer_len, "%" PRIu64 " TB(s)", size>>  40);
> +    }
> +}

This will show 1.5GB as 1GB.  Need either floating point with a couple 
of digits of precision, or show 1.5GB as 1500MB.

It also misuses SI prefixes. 1 GB means 10^9 bytes, not 2^30 bytes (with 
a common exception for RAM which is usually packaged in 1.125 times some 
power of two).

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.