Re: [PATCH] util/hexdump: fix QEMU_HEXDUMP_LINE_WIDTH logic

["Ján Tomko" <jtomko@redhat.com>]

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On a Monday in 2025, Daniel P. Berrangé wrote:
>On Fri, Sep 05, 2025 at 05:20:06PM +0300, Vladimir Sementsov-Ogievskiy wrote:
>> QEMU_HEXDUMP_LINE_WIDTH calculation doesn't correspond to
>> qemu_hexdump_line(). This leads to last line of the dump (when
>> length is not multiply of 16) has badly aligned ASCII part.
>>
>> Let's calculate length the same way.
>>
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
>> ---
>>  util/hexdump.c | 38 ++++++++++++++++++++++++--------------
>>  1 file changed, 24 insertions(+), 14 deletions(-)
>
>Would you mind also adding a test to tests/unit/test-cutils.c
>to show the correctness, as this is a nice standalone func
>we ought to be unit testing.
>
>>
>> diff --git a/util/hexdump.c b/util/hexdump.c
>> index f29ffceb74..7cfc547261 100644
>> --- a/util/hexdump.c
>> +++ b/util/hexdump.c
>> @@ -30,14 +43,8 @@ GString *qemu_hexdump_line(GString *str, const void *vbuf, size_t len,
>>
>>      if (str == NULL) {
>>          /* Estimate the length of the output to avoid reallocs. */
>> -        size_t est = len * 2;
>> -        if (unit_len) {
>> -            est += len / unit_len;
>> -        }
>> -        if (block_len) {
>> -            est += len / block_len;
>> -        }
>> -        str = g_string_sized_new(est + 1);
>> +        str = g_string_sized_new(hexdump_line_length(len, unit_len, block_len)
>> +                                 + 1);

Fun fact: with new enough glib, this will allocate a buffer of 128 bytes (nearest
power of 64+1) anyway:
https://gitlab.gnome.org/GNOME/glib/-/commit/7fc7c57b6fd470bbee267471a61c714f3a0d281c

Jano

>>      }
>>
>>      for (u = 0, b = 0; len; u++, b++, len--, buf++) {

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