printk: nbcon: Add sequence handling

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Add an atomic_long_t field @nbcon_seq to the console struct to
store the sequence number for nbcon consoles. For nbcon consoles
this will be used instead of the non-atomic @seq field. The new
field allows for safe atomic sequence number updates without
requiring any locking.

On 64bit systems the new field stores the full sequence number.
On 32bit systems the new field stores the lower 32 bits of the
sequence number, which are expanded to 64bit as needed by
folding the values based on the sequence numbers available in
the ringbuffer.

For 32bit systems, having a 32bit representation in the console
is sufficient. If a console ever gets more than 2^31 records
behind the ringbuffer then this is the least of the problems.

Co-developed-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Thomas Gleixner (Intel) <tglx@linutronix.de>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20230916192007.608398-7-john.ogness@linutronix.de

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This commit is contained in:

Thomas Gleixner 2023-09-16 21:26:05 +02:06 • committed by Petr Mladek

parent 4b08d9e24f

commit ad56ebd1d7

4 changed files with 136 additions and 7 deletions

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4

include/linux/console.h

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7

kernel/printk/internal.h

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101

kernel/printk/nbcon.c

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31

kernel/printk/printk.c

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