Messages in this thread Patch in this message | | | Date | Tue, 4 Aug 2020 12:14:00 +0200 | From | Petr Mladek <> | Subject | Re: [PATCH v2][next] printk: ringbuffer: support dataless records |
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On Tue 2020-07-21 15:31:28, John Ogness wrote: > With commit ("printk: use the lockless ringbuffer"), printk() > started silently dropping messages without text because such > records are not supported by the new printk ringbuffer. > > Add support for such records. > > Currently dataless records are denoted by INVALID_LPOS in order > to recognize failed prb_reserve() calls. Change the ringbuffer > to instead use two different identifiers (FAILED_LPOS and > NO_LPOS) to distinguish between failed prb_reserve() records and > successful dataless records, respectively. > > diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c > index 7355ca99e852..0659b50872b5 100644 > --- a/kernel/printk/printk_ringbuffer.c > +++ b/kernel/printk/printk_ringbuffer.c > static bool data_check_size(struct prb_data_ring *data_ring, unsigned int size) > { > struct prb_data_block *db = NULL; > > - /* > - * Writers are not allowed to write data-less records. Such records > - * are used only internally by the ringbuffer to denote records where > - * their data failed to allocate or have been lost. > - */ > if (size == 0) > - return false; > + return true;
Nit: This might deserve a comment why size == 0 is handled a special way.specially. I think about something like:
/* * Empty data blocks are handled by special lpos values in * the record descriptor. No space is needed in the data ring. */
or simply
/* Data-less records take no space in the data ring. */
> /* > * Ensure the alignment padded size could possibly fit in the data
> @@ -1025,6 +1020,10 @@ static char *data_alloc(struct printk_ringbuffer *rb, > static unsigned int space_used(struct prb_data_ring *data_ring, > struct prb_data_blk_lpos *blk_lpos) > { > + /* Data-less blocks take no space. */ > + if (LPOS_DATALESS(blk_lpos->begin)) > + return 0;
Nit: It seems that all the other locations check also blk_lpos->next, for example, get_data() does:
if (LPOS_DATALESS(blk_lpos->begin) && LPOS_DATALESS(blk_lpos->next)) {
Both approaches are error prone. I would either simplify the other locations and check only lpos->begin. But better might be to be on the safe side do a paranoid check, like: bool is_dataless(struct prb_data_blk_lpos *blk_lpos) { if (LPOS_DATALESS(blk_lpos->begin) || LPOS_DATALESS(blk_lpos->next)) { WARN_ON_ONCE(blk_lpos->begin != blk_lpos->next); return true; } return false; } > + > if (DATA_WRAPS(data_ring, blk_lpos->begin) == DATA_WRAPS(data_ring, blk_lpos->next)) { > /* Data block does not wrap. */ > return (DATA_INDEX(data_ring, blk_lpos->next) -
Anyway, the patch looks fine. It is already pushed in printk/linux.git. So, if you agree with my nits, we should solve them with separate patches on top of the existing ones.
Best Regards, Petr
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