linux-kernel - Re: [Xen-devel] [PATCH] xen/hvc: If we use xen_raw

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Date:	Wed, 21 Aug 2013 06:44:24 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Ian Campbell <ian.campbell@...rix.com>
CC:	xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] [PATCH] xen/hvc: If we use xen_raw_printk let it also work on HVM guests.

Ian Campbell <ian.campbell@...rix.com> wrote:
>On Tue, 2013-08-20 at 15:35 -0400, Konrad Rzeszutek Wilk wrote:
>>  void xen_raw_console_write(const char *str)
>>  {
>> -	dom0_write_console(0, str, strlen(str));
>> +	ssize_t len = strlen(str);
>> +	int rc = 0;
>> +
>> +	if (xen_domain()) {
>> +		rc = dom0_write_console(0, str, len);
>> +		if (rc != len && xen_hvm_domain()) /* -ENOSYS */
>
>If you want to catch ENOSYS then I suggest doing so explicitly, rather
>that relying on len != -ENOSYS.
>
>> +			goto outb_print;
>
>How about reversing this into
>	if (rc == len) return;
>	if (rc != -ENOSYS) panic(...) /* yes, this won't get far... *.
>
>Then fall through to the following block as a plain if not an else if.
>Maybe with a xen_hvm_domain && added.
>
>That avoids the yucky goto I think.
>
>> +	} else if (xen_cpuid_base()) {
>> +		int i;
>> +outb_print:
>> +		for (i = 0; i < len; i++)
>> +			outb(str[i], 0xe9);
>> +	}
>>  }
>>  
>>  void xen_raw_printk(const char *fmt, ...)

B/c the function  dom0_write_console never returns negative values.  Instead it converts it to a zero return value. Perhaps it can return negative values -  will have to look. 
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