Messages in this thread | | | Date | Fri, 16 Jun 2017 11:00:54 +0900 | From | Sergey Senozhatsky <> | Subject | Re: [PATCH 3/3] printk/console: Always have a preferred console |
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On (06/15/17 16:54), Petr Mladek wrote: > On Wed 2017-06-14 18:11:28, Sergey Senozhatsky wrote: > > On (06/13/17 14:54), Petr Mladek wrote: > > > > > This patch modifies the code that enables the configured consoles. > > > It sets the CON_CONSDEV flag also when we register the first > > > console. It causes that one of the registered consoles will > > > always have CON_CONSDEV flag set. > > > > hm.... my impression was that we shouldn't set CON_CONSDEV if the > > console has no ->device. but then, once again, unregister_console() > > does not care and register_console() cares only in one place. so I'm > > a bit in doubt. > > Great catch! It helped me to get even better picture. > > If I get it correctly, the console driver for /dev/console is > found in tty_lookup_driver() by console_device(). Where > console_device() skips console drivers without any device. > > CON_CONSDEV is basically handled only in register_console() > and unregister_console(). The driver with this flag is kept at > the beginning of the console_drivers list. It causes that > console_device() will return the console with this flag.
yeah, I grep-ed and didn't find anything that would depend on CON_CONSDEV flag (except for printk), we check ->device in critical places.
> Also it is in sync with the commit cd3a1b8562d28490b33 ("printk: don't > prefer unsuited consoles on registration"). It added the check > for existing device into the fallback code in console_register() > so that console_device() might find a valid one. > > BTW: The flag CON_CONSDEV first appeared in Linux 2.1.92. > It replaced CON_FIRST. Documentation/serial-console.txt > was modified so that the last console on the command line > will be used for /dev/console instead of the first one.
good to know that, thanks. s/CON_FIRST/CON_LAST/g :)
> In each case, it seems that CON_CONSDEV is closely related > to an existing device and does not make much sense without it. > > > Heh, the handling in unregister_console() looks buggy. Well, > it probably does not break anything. The function does not change > the order of drivers and console_device() searches > the entire list until it finds a console with device.
yep. seems so.
-ss
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