Re: [PATCH v3 3/3] printk: fix double printing with earlycon

Sergey Senozhatsky
2017-03-08T05:33:37Z

Hello,

sorry for the delay.

On (03/07/17 15:54), Aleksey Makarov wrote:
> On 03/06/2017 03:59 PM, Sergey Senozhatsky wrote:
> > On (03/03/17 18:49), Aleksey Makarov wrote:
> > [..]
> > > +static enum { CONSOLE_MATCH, CONSOLE_MATCH_RETURN, CONSOLE_MATCH_NEXT }
> > > +match_console(struct console *newcon, struct console_cmdline *c)
> >
> > that enum in function return is interesting :)
> > can we make it less hackish?
> We probably can, but I can not figure out how to do that.
> Suggestions will be appreciated.
> We should signal 3 different outcomes.
> I thought that using standard errnos is not quite desciptive.

no problems with the enum on its own. errnos probably can also do
the trick.

the way it's defined, however, is a bit unusual and may be
inconvenient - we can add, say, 5 more CONSOLE_MATCH_FOO someday
in the future and match_console() function definition thus will be:

static enum { CONSOLE_MATCH, CONSOLE_MATCH_RETURN, CONSOLE_MATCH_NEXT,
CONSOLE_MATCH_FOO1, CONSOLE_MATCH_FOO2,
CONSOLE_MATCH_FOO3, CONSOLE_MATCH_FOO4,
CONSOLE_MATCH_FOO5}
match_console(struct console *newcon, struct console_cmdline *c)
{
...
}

or something like this

static enum { CONSOLE_MATCH,
CONSOLE_MATCH_RETURN,
CONSOLE_MATCH_NEXT,
CONSOLE_MATCH_FOO1,
CONSOLE_MATCH_FOO2,
CONSOLE_MATCH_FOO3,
CONSOLE_MATCH_FOO4,
CONSOLE_MATCH_FOO5 }
match_console(struct console *newcon, struct console_cmdline *c)
{
..
}

or anything else. which is, to my admittedly imperfect taste, slightly
"unpretty".

[..]
> > > + /*
> > > * See if this console matches one we selected on
> > > * the command line.
> > > */
> > > for (i = 0, c = console_cmdline;
> > > i < MAX_CMDLINECONSOLES && c->name[0];
> > > i++, c++) {
> > > - if (!newcon->match ||
> > > - newcon->match(newcon, c->name, c->index, c->options) != 0) {
> > > - /* default matching */
> > > - BUILD_BUG_ON(sizeof(c->name) != sizeof(newcon->name));
> > > - if (strcmp(c->name, newcon->name) != 0)
> > > - continue;
> > > - if (newcon->index >= 0 &&
> > > - newcon->index != c->index)
> > > - continue;
> > > - if (newcon->index < 0)
> > > - newcon->index = c->index;
> > > -
> > > - if (_braille_register_console(newcon, c))
> > > - return;
> > >
> > > - if (newcon->setup &&
> > > - newcon->setup(newcon, c->options) != 0)
> > > - break;
> > > - }
> > > + if (preferred_console == i)
> > > + continue;
> > >
> > > - newcon->flags |= CON_ENABLED;
> > > - if (i == preferred_console) {
> > > - newcon->flags |= CON_CONSDEV;
> > > - has_preferred = true;
> > > + switch (match_console(newcon, c)) {
> > > + case CONSOLE_MATCH:
> > > + goto match;
> > > + case CONSOLE_MATCH_RETURN:
> > > + return;
> > > + default:
> > > + break;
> >
> > sorry, it was a rather long for me today. need to look more at this.
> > for what is now CONSOLE_MATCH_NEXT we used to have continue,
>
> CONSOLE_MATCH is for the case when the console matches against the description,
> CONSOLE_MATCH_NEXT - it does not, we should try next,

my bad, sorry. I misread the patch: there was another `break' right after
that switch, that you have removed; and I just wrongly concluded that
CONSOLE_MATCH_NEXT would now 'break' from 'default' label *and* `break'
from the console_cmdline loop right after it.

bikeshedding:
may be explicit CONSOLE_MATCH_NEXT test will save us from problems (in
case if match_console() will return more codes someday), may be it won't.
hard to say. 'default: continue' is probably OK. or may be can do without
that 'match' label at all. something like this (_may be_)

for (i = 0, c = console_cmdline; ... ) {
if (preferred_console == i)
continue;

match = match_console(newcon, c);
if (match == CONSOLE_MATCH_NEXT)
continue;
if (match == CONSOLE_MATCH_FOUND)
break;
if (match == CONSOLE_MATCH_STOP)
return;
}
...

CONSOLE_MATCH_RETURN - basically means that we should stop matching.
can we thus rename it to CONSOLE_MATCH_STOP, or similar?

match_console() returned CONSOLE_MATCH_STOP

is a bit better than

match_console() returned CONSOLE_MATCH_RETURN.

isn't it? :)

// I also used CONSOLE_MATCH_FOUND in the example above instead of
// CONSOLE_MATCH. not insisting that CONSOLE_MATCH_FOUND is much
// better than CONSOLE_MATCH though.

-ss