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SubjectRe: [PATCH printk v5 5/6] printk: ringbuffer: add finalization/extension support
On Mon 2020-09-14 14:39:53, John Ogness wrote:
> Add support for extending the newest data block. For this, introduce
> a new finalization state (desc_finalized) denoting a committed
> descriptor that cannot be extended.
>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>

Looks good to me:

Reviewed-by: Petr Mladek <pmladek@suse.com>

There seems to be possible a small clean up, see below. But I would do
it in a followup patch to avoid yet another respin.


> diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
> index 911fbe150e9a..4e526c79f89c 100644
> --- a/kernel/printk/printk_ringbuffer.c
> +++ b/kernel/printk/printk_ringbuffer.c
> +/*
> + * Try to resize an existing data block associated with the descriptor
> + * specified by @id. If the resized data block should become wrapped, it
> + * copies the old data to the new data block. If @size yields a data block
> + * with the same or less size, the data block is left as is.
> + *
> + * Fail if this is not the last allocated data block or if there is not
> + * enough space or it is not possible make enough space.
> + *
> + * Return a pointer to the beginning of the entire data buffer or NULL on
> + * failure.
> + */
> +static char *data_realloc(struct printk_ringbuffer *rb,
> + struct prb_data_ring *data_ring, unsigned int size,
> + struct prb_data_blk_lpos *blk_lpos, unsigned long id)
> +{
> + struct prb_data_block *blk;
> + unsigned long head_lpos;
> + unsigned long next_lpos;
> + bool wrapped;
> +
> + /* Reallocation only works if @blk_lpos is the newest data block. */
> + head_lpos = atomic_long_read(&data_ring->head_lpos);
> + if (head_lpos != blk_lpos->next)
> + return NULL;
> +
> + /* Keep track if @blk_lpos was a wrapping data block. */
> + wrapped = (DATA_WRAPS(data_ring, blk_lpos->begin) != DATA_WRAPS(data_ring, blk_lpos->next));
> +
> + size = to_blk_size(size);
> +
> + next_lpos = get_next_lpos(data_ring, blk_lpos->begin, size);
> +
> + /* If the data block does not increase, there is nothing to do. */
> + if (head_lpos - next_lpos < DATA_SIZE(data_ring)) {
> + blk = to_block(data_ring, blk_lpos->begin);
> + return &blk->data[0];
> + }
> +
> + if (!data_push_tail(rb, data_ring, next_lpos - DATA_SIZE(data_ring)))
> + return NULL;
> +
> + /* The memory barrier involvement is the same as data_alloc:A. */
> + if (!atomic_long_try_cmpxchg(&data_ring->head_lpos, &head_lpos,
> + next_lpos)) { /* LMM(data_realloc:A) */
> + return NULL;
> + }
> +
> + blk = to_block(data_ring, blk_lpos->begin);
> +
> + if (DATA_WRAPS(data_ring, blk_lpos->begin) != DATA_WRAPS(data_ring, next_lpos)) {
> + struct prb_data_block *old_blk = blk;
> +
> + /* Wrapping data blocks store their data at the beginning. */
> + blk = to_block(data_ring, 0);
> +
> + /*
> + * Store the ID on the wrapped block for consistency.
> + * The printk_ringbuffer does not actually use it.
> + */
> + blk->id = id;

Small cleanup: The "id" should already be there when the block has
already been wrapped before. By other words, even the above
need to be done only when (!wrapped).

> +
> + if (!wrapped) {
> + /*
> + * Since the allocated space is now in the newly
> + * created wrapping data block, copy the content
> + * from the old data block.
> + */
> + memcpy(&blk->data[0], &old_blk->data[0],
> + (blk_lpos->next - blk_lpos->begin) - sizeof(blk->id));
> + }
> + }
> +
> + blk_lpos->next = next_lpos;
> +
> + return &blk->data[0];
> +}
> +
> /* Return the number of bytes used by a data block. */
> static unsigned int space_used(struct prb_data_ring *data_ring,
> struct prb_data_blk_lpos *blk_lpos)

Best Regards,
Petr

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