When the tracepoint was introduced in 8f37f5c2a5,
the connect_block duration was passed in microseconds `µs`.
By starting to use steady clock in fabf1cdb20
this changed to nanoseconds `ns`. As the test only checked if the
duration value is `> 0` as a plausibility check, this went unnoticed.
I detected this when setting up monitoring for block validation time
as part of the Great Consensus Cleanup Revival discussion.
This change casts the duration explicitly to nanoseconds (as it has been
nanoseconds for the last three releases; switching back now would 'break'
the broken API again; there don't seem to be many users affected), updates
the documentation and adds a check for an upper bound to the tracepoint
interface tests. The upper bound is quite lax as mining the block takes
much longer than connecting the empty test block. It's however able to
detect incorrect duration units passed.
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.
