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    SubjectRe: [PATCH printk v2 2/8] printk: Provide debug_store() for nbcon debugging
    On Fri 2023-07-28 02:08:27, John Ogness wrote:
    > To debug and validate nbcon ownership transitions, provide a new
    > macro debug_store() (enabled with DEBUG_NBCON) to log transition
    > information to the ringbuffer. If enabled, this macro only logs
    > to the ringbuffer and does not trigger any printing. This is to
    > avoid triggering recursive printing in the nbcon consoles.
    >
    > --- a/kernel/printk/printk_nbcon.c
    > +++ b/kernel/printk/printk_nbcon.c
    > @@ -10,6 +10,35 @@
    > * the legacy style console_lock mechanism.
    > */
    >
    > +/*
    > + * Define DEBUG_NBCON to allow for nbcon ownership transitions to be logged
    > + * to the ringbuffer. The debug_store() macro only logs to the lockless
    > + * ringbuffer and does not trigger any printing.
    > + */
    > +#undef DEBUG_NBCON
    > +
    > +#ifdef DEBUG_NBCON
    > +/* Only write to ringbuffer. */
    > +int __debug_store(const char *fmt, ...)
    > +{
    > + va_list args;
    > + int r;
    > +
    > + va_start(args, fmt);
    > + r = vprintk_store(2, 7, NULL, fmt, args);

    I have never used the facility number before. It seems that they are
    defined in /usr/include/sys/syslog.h, for example, see
    https://sites.uclouvain.be/SystInfo/usr/include/sys/syslog.h.html

    They are even somehow documented in "man 3 syslog", for example, see
    https://linux.die.net/man/3/syslog

    We should probably use one of the LOG_LOCALX numbers, e.g.

    #define LOG_LOCAL0 (16<<3)

    Also, please use LOGLEVEL_DEBUG instead of the hard coded "7".

    > + va_end(args);
    > +
    > + return r;
    > +}
    > +#define debug_store(cond, fmt, ...) \
    > + do { \
    > + if (cond) \
    > + __debug_store(pr_fmt("DEBUG: " fmt), ##__VA_ARGS__) \
    > + } while (0)
    > +#else
    > +#define debug_store(cond, fmt, ...)
    > +#endif
    > +
    > /**
    > * nbcon_state_set - Helper function to set the console state
    > * @con: Console to update

    Best Regards,
    Petr

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