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


From: Bihong Yu
Subject: Re: [PATCH v1 2/8] migration: Don't use '#' flag of printf format
Date: Mon, 12 Oct 2020 20:45:41 +0800
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0

Thank you for your review. OK,I have fixed the problem in v2.

On 2020/10/12 2:19, Peter Maydell wrote:
> On Sun, 11 Oct 2020 at 14:52, Bihong Yu <yubihong@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
> .
> 



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