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SubjectRe: [PATCH v8 3/3] printk: fix double printing with earlycon
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On 03/27/2017 05:14 PM, Petr Mladek wrote:
> On Mon 2017-03-20 13:03:00, Aleksey Makarov wrote:

[..]

>> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
>> index fd752f0c8ef1..462036e7a767 100644
>> --- a/kernel/printk/printk.c
>> +++ b/kernel/printk/printk.c
>> @@ -1909,8 +1909,28 @@ static int __add_preferred_console(char *name, int idx, char *options,
>> i < MAX_CMDLINECONSOLES && c->name[0];
>> i++, c++) {
>> if (strcmp(c->name, name) == 0 && c->index == idx) {
>> - if (!brl_options)
>> - preferred_console = i;
>> + int last;
>> +
>> + if (brl_options)
>> + return 0;
>> +
>> + /*
>> + * Maintain an invariant that will help to find if
>> + * the matching console is preferred, see
>> + * register_console():
>> + *
>> + * The last non-braille console is always
>> + * the preferred one.
>> + */
>> + for (last = MAX_CMDLINECONSOLES - 1;
>> + last >= 0 && !console_cmdline[last].name[0];
>> + last--)
>> + ;
>
> This is a rather non-trivial code to find the last element.
> I might make sense to count it in a global variable.
> Then we might remove the check for console_cmdline[i].name[0]
> also in the other for cycles and make them better readable.

Having an additional variable console_cmdline_last pointing to the last element
would require maintaining consistency between this variable and
contents of console_cmdline. For the code we have it is not hard, but when code
is changed we need to check this. Also there exists preferred_console that
has almost the same meaning but it points not to the last element, but to the
last non-braille element. Also we need to have a special value (-1) for this
variable for empty array. So I personally would instead try to rewrite this:

for (last = MAX_CMDLINECONSOLES - 1; last >= 0; last--)
if (console_cmdline[last].name[0])
break;

Is it better? If not, I will send a version with console_cmdline_last.

>> +
>> + if (i != last)
>> + swap(console_cmdline[i], console_cmdline[last]);
>
> I was not aware of the swap() function. It is great to know ;-)

Yes, same for me. Thanks to Sergey Senozhatsky.

Thank you for review
Aleksey Makarov

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