Messages in this thread | | | Date | Thu, 30 Jan 2020 15:39:18 +0200 | From | Andy Shevchenko <> | Subject | Re: [PATCH v3 5/5] console: Introduce ->exit() callback |
| |
On Thu, Jan 30, 2020 at 02:22:46PM +0100, Petr Mladek wrote: > On Wed 2020-01-29 16:25:58, Andy Shevchenko wrote: > > On Wed, Jan 29, 2020 at 10:41:41PM +0900, Sergey Senozhatsky wrote: > > > On (20/01/28 11:44), Andy Shevchenko wrote:
...
> > > > > If the console was not registered (hence not enabled) is it still required > > > > > to call ->exit()? Is there a requirement that ->exit() should handle such > > > > > cases? > > > > > > > > This is a good point. The ->exit() purpose is to keep balance for whatever > > > > happened at ->setup(). > > > > > > > > But ->setup() is being called either when we have has_preferred == false or > > > > when we got no matching we call it for all such consoles, till it returns an > > > > error (can you elaborate the logic behind it?). > > > > > > ->match() does alias matching and ->setup(). If alias matching failed, > > > exact name match takes place. We don't call ->setup() for all consoles, > > > but only for those that have exact name match: > > > > > > if (strcmp(c->name, newcon->name) != 0) > > > continue; > > > > > > As to why we don't stop sooner in that loop - I need to to do some > > > archaeology. We need to have CON_CONSDEV at proper place, which is > > > IIRC the last matching console. > > > > > > Pretty much every time we tried to change the logic we ended up > > > reverting the changes. > > > > I understand. Seems the ->setup() has to be idempotent. We can tell the same > > for ->exit() in some comment. > > I believe that ->setup() can succeesfully be called only once. > It is tricky like hell:
Indeed. I think this code is highly starving for comments.
> 1st piece: > > if (!has_preferred || bcon || !console_drivers) > has_preferred = preferred_console >= 0; > > note: > > + "has_preferred" is updated here only when it was not "true" before. > + "has_preferred" is set to "true" here only when "preferred_console" > is set in __add_preferred_console() > > 2nd piece: > > + __add_preferred_console() is called for console defined on > the command line. "preferred_console" points to the console > defined by the last "console=" parameter. > > 3rd piece: > > + "has_preferred" is set to "true" later in register_console() when > a console with tty binding gets enabled. > > 4th piece: > > + The code: > > /* > * See if we want to use this console driver. If we > * didn't select a console we take the first one > * that registers here. > */ > if (!has_preferred) > ... try to enable the given console > > The comment is a bit unclear. The code is used as a fallback > when no console was defined on the command line. > > Note that "has_preferred" is always true when "preferred_console" > was defined via command line, see 2nd piece above. > > > By other words: > > + The fallback code (4th piece) is called only when > "preferred_console" was not defined on the command line. > > + The cycle below matches the given console only when > it was defined on the command line. > > > As a result, I believe that ->setup() could never be called > in both paths for the same console. Especially I think that > fallback code should not be used when the console was defined on > the command line. > > I am not 100% sure but I am ready to risk this. Anyway, I think > that many ->setup() callbacks are not ready to be successfully > called twice. > > (Sigh, I have started to clean up this code two years ago. > But I have never found time to finish the patchset. It is > such a huge mess.)
Thanks for the elaboration in such details!
> > Can you describe, btw, struct console in kernel doc format? > > It will be very helpful! > > > > > > In both cases we will get the console to have CON_ENABLED flag set. > > > > > > And there are sneaky consoles that have CON_ENABLED before we even > > > register them. > > > > So, taking into consideration my comment to the previous patch, what would be > > suggested guard here? > > > > For a starter something like this? > > > > if ((console->flags & CON_ENABLED) && console->exit) > > console->exit(console); > > I would do: > > if (!res && console->exit) > console->exit(console); > > I mean. I would call ->exit() only when console->setup() succeeded in > register_console(). In this case, the console was later added to > the console_drivers list.
Yes, that is exactly what I meant in previous mails to you.
-- With Best Regards, Andy Shevchenko
| |