tree 2c7fcde348cb94930fb52f1113ecb47d9348b1a4
parent 2d4fa78d91e9cb9f65c0dcaebc6ebfae8350953f
author Prashanth Swaminathan <prashanthsw@google.com> 1624292545 -0700
committer CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com> 1626197836 +0000

pw_ring_buffer: Add ring buffer iterator

To support walking through the ring buffers in crash contexts, it's
useful to have a mechanism that allows processing entries in the ring
buffer without requiring buffer copies (in favor of raw access). This
adds a new unsafe iteration class that can be used while the caller has
a guarantee that the underlying buffer is not being mutated.

The multisink is also updated to support this unsafe iteration by adding
an oldest entry reader that is used as a reference point for the
iterator class. This will additionally support late-drain attach flows
where a drain may want to match the oldest entry available in the
buffer, as opposed to the current logic that always starts it at the
write index.

Bug: b/190547664
Change-Id: I430bab37b47630dbdfba184ad94f818a5225f79a
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/50262
Commit-Queue: Prashanth Swaminathan <prashanthsw@google.com>
Reviewed-by: Wyatt Hepler <hepler@google.com>
Reviewed-by: Ewout van Bekkum <ewout@google.com>