USDT probes are statically defined trace points that have nearly zero
disabled-probe effect, i.e. we can put them in hot paths.
The use case for these is both similar and dissimilar to Rust tracing:
We still need better logging and a better structured rust-tracing
looking thing, but probes allow for quite easy programmable interactive
tracing in production, which we also care a lot about.
This CL comes with a perfunctory trace point in
libstore/file-transfer.cc for reading data out of the curl buffer. This
was mostly thrown in there so that I could see what the buffer sizes of
this were, and maybe be able to instrument the perf of the curl usages
in Lix in the future.
Fixes: https://git.lix.systems/lix-project/lix/issues/727
Change-Id: I0f5d9912d76bf3d6923bf53ebfd9b8d6c6e70aea
Jade Lovelace
cad275307e