Re: [PATCH printk v3 33/40] printk, xen: fbfront: create/use safe function for forcing preferred

On 2022-11-10, Petr Mladek [off-list ref] wrote:

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+	/* Only the new head can have CON_CONSDEV set. */
+	WRITE_ONCE(cur_pref_con->flags, cur_pref_con->flags & ~CON_CONSDEV);

As mentioned in the reply for 7th patch, I would prefer to hide this
WRITE_ONCE into a wrapper, e.g. console_set_flag(). It might also
check that the console_list_lock is taken...

Agreed. For v4 it will become:

console_srcu_write_flags(cur_pref_con, cur_pref_con->flags & ~CON_CONSDEV);

I am happy that your are going to introduce an API for this.

Just to be sure. The _srcu_ in the name means that the write
will use WRITE_ONCE() so that it can be read safely in SRCU
context using READ_ONCE(). Do I get it correctly, please?

Yes.

I expect that the counter part will be console_srcu_read_flags().
I like the name. It is better than _unsafe_ that I proposed earlier.

Since the only flag that is ever checked in this way is CON_ENABLED, I
was planning on calling it console_srcu_is_enabled(). But I suppose I
could have it be: (console_srcu_read_flags() & CON_ENABLED). That would
keep it more abstract in case anyone should want to read other flag bits
under SRCU.

There are only 4 call sites that need this, so I suppose we don't need a
special _is_enabled() variant. Thanks for the suggestion!

John