Re: [PATCH v1 2/8] migration: Don't use '#' flag of printf format

[Peter Maydell]

On Sun, 11 Oct 2020 at 14:52, Bihong Yu <yubih...@huawei.com> wrote:
> @@ -998,7 +998,7 @@ static int block_load(QEMUFile *f, void *opaque, int 
> version_id)
>                     (addr == 100) ? '\n' : '\r');
>              fflush(stdout);
>          } else if (!(flags & BLK_MIG_FLAG_EOS)) {
> -            fprintf(stderr, "Unknown block migration flags: %#x\n", flags);
> +            fprintf(stderr, "Unknown block migration flags: %0x\n", flags);

This doesn't look right. "%#x" will print a number in hex with a leading '0x'.
To get the same effect without using "#" you need "0x%x" (that is,
the format string provides the 0x characters literally).
What you've written is '%0x", which is a format string where the '0' is
a request to print with zero padding (which is ignored since there's no
field width given), so the result is the same as if you'd just said '%x',
and there is no '0x' in the output.

$ cat /tmp/zz9.c
#include <stdio.h>
int main(void) {
  printf("%#x\n", 42);
  printf("%0x\n", 42);
  printf("0x%x\n", 42);
  return 0;
}
$ gcc -g -Wall -o /tmp/zz9 /tmp/zz9.c
$ /tmp/zz9
0x2a
2a
0x2a

>          default:
> -            error_report("Unknown combination of migration flags: %#x"
> +            error_report("Unknown combination of migration flags: %0x"
>                           " (postcopy mode)", flags);
>              ret = -EINVAL;
>              break;
> @@ -3576,7 +3576,7 @@ static int ram_load_precopy(QEMUFile *f)
>              if (flags & RAM_SAVE_FLAG_HOOK) {
>                  ram_control_load_hook(f, RAM_CONTROL_HOOK, NULL);
>              } else {
> -                error_report("Unknown combination of migration flags: %#x",
> +                error_report("Unknown combination of migration flags: %0x",
>                               flags);
>                  ret = -EINVAL;
>              }

These two similarly should be "0x%x".

thanks
-- PMM