CmdName previously opened the running executable and streamed through
tens of MB searching for two 16-byte magic needles to find the Go
module info blob embedded by the linker, allocating a 64 KiB buffer on
every call. It was called at least twice during tailscaled startup
(logpolicy.LogsDir and logpolicy.Options.init on Windows) and once
more for tsweb's debug page title -- each call ~2.6 ms on a ~40 MB
tailscaled binary, and ~74 KB of allocator churn per call.
The same module info is exposed via runtime/debug.ReadBuildInfo, which
reads an already-resident string maintained by the Go runtime -- no
filesystem I/O. Use that, cached with sync.OnceValue so the lookup
happens at most once per process.
Benchmarks on Xeon 6975P-C (Linux amd64), against the version test
binary:
BenchmarkCmdName before: 540,094 ns/op 66,136 B/op 8 allocs/op
BenchmarkCmdName after: 2.5 ns/op 0 B/op 0 allocs/op
First-call (uncached) cost at tailscaled scale (71 deps in embedded
build info): 160 mallocs, ~11.5 KiB allocated, sub-microsecond. That
is smaller than the single 64 KiB scratch buffer the old code
allocated per call, and is now paid exactly once per process.
Stripped tailscaled binary size is unchanged: runtime/debug was
already imported transitively (including by sibling code in this same
package at version/version.go:121), so no new dependencies ship. The
hand-rolled byte scanner, 64 KiB scratch buffer, rsc.io/goversion-
derived magic constants, and the 32-second integration test that
built tailscaled to re-parse it are removed.
TestCmdNameNoAllocs asserts that, once primed, CmdName is 0 allocs
per call, guarding against regressions that reintroduce per-call
binary parsing. TestCmdNameFromBuildInfo verifies that CmdName is
pulling from the embedded build info rather than falling back to the
os.Executable basename.
This file was never truly necessary and has never actually been used in
the history of Tailscale's open source releases.
A Brief History of AUTHORS files
---
The AUTHORS file was a pattern developed at Google, originally for
Chromium, then adopted by Go and a bunch of other projects. The problem
was that Chromium originally had a copyright line only recognizing
Google as the copyright holder. Because Google (and most open source
projects) do not require copyright assignemnt for contributions, each
contributor maintains their copyright. Some large corporate contributors
then tried to add their own name to the copyright line in the LICENSE
file or in file headers. This quickly becomes unwieldy, and puts a
tremendous burden on anyone building on top of Chromium, since the
license requires that they keep all copyright lines intact.
The compromise was to create an AUTHORS file that would list all of the
copyright holders. The LICENSE file and source file headers would then
include that list by reference, listing the copyright holder as "The
Chromium Authors".
This also become cumbersome to simply keep the file up to date with a
high rate of new contributors. Plus it's not always obvious who the
copyright holder is. Sometimes it is the individual making the
contribution, but many times it may be their employer. There is no way
for the proejct maintainer to know.
Eventually, Google changed their policy to no longer recommend trying to
keep the AUTHORS file up to date proactively, and instead to only add to
it when requested: https://opensource.google/docs/releasing/authors.
They are also clear that:
> Adding contributors to the AUTHORS file is entirely within the
> project's discretion and has no implications for copyright ownership.
It was primarily added to appease a small number of large contributors
that insisted that they be recognized as copyright holders (which was
entirely their right to do). But it's not truly necessary, and not even
the most accurate way of identifying contributors and/or copyright
holders.
In practice, we've never added anyone to our AUTHORS file. It only lists
Tailscale, so it's not really serving any purpose. It also causes
confusion because Tailscalars put the "Tailscale Inc & AUTHORS" header
in other open source repos which don't actually have an AUTHORS file, so
it's ambiguous what that means.
Instead, we just acknowledge that the contributors to Tailscale (whoever
they are) are copyright holders for their individual contributions. We
also have the benefit of using the DCO (developercertificate.org) which
provides some additional certification of their right to make the
contribution.
The source file changes were purely mechanical with:
git ls-files | xargs sed -i -e 's/\(Tailscale Inc &\) AUTHORS/\1 contributors/g'
Updates #cleanup
Change-Id: Ia101a4a3005adb9118051b3416f5a64a4a45987d
Signed-off-by: Will Norris <will@tailscale.com>
This updates all source files to use a new standard header for copyright
and license declaration. Notably, copyright no longer includes a date,
and we now use the standard SPDX-License-Identifier header.
This commit was done almost entirely mechanically with perl, and then
some minimal manual fixes.
Updates #6865
Signed-off-by: Will Norris <will@tailscale.com>
