799968e8b3 tracing: misc follow-ups to 22902 (0xb10c)
36a6584703 tracing: correctly scope utxocache:flush tracepoint (Arnab Sen)
Pull request description:
This PR is a follow-up to the [#22902](https://github.com/bitcoin/bitcoin/pull/22902).
Previously, the tracepoint `utxocache:flush` was called, even when it was not flushing. So, the tracepoint is now scoped to write only when coins cache to disk.
ACKs for top commit:
0xB10C:
ACK 799968e8b3
Tree-SHA512: ebb096cbf991c551c81e4339821f10d9768c14cf3d8cb14d0ad851acff5980962228a1c746914c6aba3bdb27e8be53b33349c41efe8bab5542f639916e437b5f
- mention 'Lost X events' workaround
- clarify flush tracepoint docs
- fix typo in tracepoint context
- clarify flush for prune
The documentation and examples for the `fFlushForPrune` argument
of the utxocache flush tracepoint weren't clear without looking
at the code.
See these comments: https://github.com/bitcoin/bitcoin/pull/22902#issuecomment-987094612
- doc: note that there can be temporary UTXO caches
Bitcoin Core uses temporary clones of it's _main_ UTXO cache in some
places. The utxocache:add and :spent tracepoints are triggered when
temporary caches are changed too. This is documented.
Previously, the `utxocache:flush` tracepoint was in the wrong scope and
reached every time `CChainState::FlushStateToDisk` was called, even when
there was no flushing of the cache. The tracepoint is now properly scoped
and will be reached during a full flush.
Inside the scope, the `fDoFullFlush` value will always be `true`, so it
doesn't need to be logged separately. Hence, it's dropped from the
tracepoint arguments.
The tracepoint `validation:block_connected` was introduced in #22006.
The first argument was the hash of the connected block as a pointer
to a C-like String. The last argument passed the hash of the
connected block as a pointer to 32 bytes. The hash was only passed as
string to allow `bpftrace` scripts to print the hash. It was
(incorrectly) assumed that `bpftrace` cannot hex-format and print the
block hash given only the hash as bytes.
The block hash can be printed in `bpftrace` by calling
`printf("%02x")` for each byte of the hash in an `unroll () {...}`.
By starting from the last byte of the hash, it can be printed in
big-endian (the block-explorer format).
```C
$p = $hash + 31;
unroll(32) {
$b = *(uint8*)$p;
printf("%02x", $b);
$p -= 1;
}
```
See also: https://github.com/bitcoin/bitcoin/pull/22902#discussion_r705176691
This is a breaking change to the block_connected tracepoint API, however
this tracepoint has not yet been included in a release.
Both added files are extended in the following commits.
doc/usdt.md is based on earlier work by laanwj.
Co-authored-by: W. J. van der Laan <laanwj@protonmail.com>
fanquake