On 2020-09-04, Petr Mladek <[email protected]> wrote: > I am currently playing with support for all three timestamps based > on https://lore.kernel.org/lkml/[email protected]/ > > And I got the following idea: > > 1. Storing side: > > Create one more ring/array for storing the optional metadata. > It might eventually replace dict ring, see below. > > struct struct printk_ext_info { > u64 ts_boot; /* timestamp from boot clock */ > u64 ts_real; /* timestamp from real clock */ > char process[TASK_COMM_LEN]; /* process name */ > }; > > It must be in a separate array so that struct prb_desc stay stable > and crashdump tools do not need to be updated so often. > > But the number of these structures must be the same as descriptors. > So it might be: > > struct prb_desc_ring { > unsigned int count_bits; > struct prb_desc *descs; > struct printk_ext_info *ext_info > atomic_long_t head_id; > atomic_long_t tail_id; > }; > > One huge advantage is that these extra information would not block > pushing lockless printk buffer upstream. > > It might be even possible to get rid of dict ring and just > add two more elements into struct printk_ext_info: > > char subsystem[16]; /* for SUBSYSTEM= dict value */ > char device[48]; /* for DEVICE= dict value */
You say "get rid of dict ring", but there is nothing requiring the dict_ring to be strings. It can be binary data. The @data of the prb_data_block struct could be a printk_ext_info struct. This would be trivial to implement in printk.c and would not require any ringbuffer changes. (My ringbuffer test software [0] uses binary structs for the data.) Using VMCOREINFO we can provide the printk_ext_info size and field offsets for crash tools. > Pros: > > + the information will always get stored If the dict_ring is "_DESCS_COUNT() * sizeof(struct printk_ext_info)" then it would also always get stored. Although this does seem like a bit of a waste of space in order to cover the worst case scenario of all records using all fields. John Ogness [0] https://github.com/Linutronix/prb-test.git
