tests/test-permissions.t

cborutil: change buffering strategy

Profiling revealed that we were spending a lot of time on the
line that was concatenating the old buffer with the incoming data
when attempting to decode long byte strings, such as manifest
revisions.

Essentially, we were feeding N chunks of size len(X) << len(Y) into
decode() and continuously allocating a new, larger buffer to hold
the undecoded input. This created substantial memory churn and
slowed down execution.

Changing the code to aggregate pending chunks in a list until we
have enough data to fully decode the next atom makes things much
more efficient.

I don't have exact data, but I recall the old code spending >1s
on manifest fulltexts from the mozilla-unified repo. The new code
doesn't significantly appear in profile output.

Differential Revision: https://phab.mercurial-scm.org/D4854

#require unix-permissions no-root reporevlogstore

  $ hg init t
  $ cd t

  $ echo foo > a
  $ hg add a

  $ hg commit -m "1"

  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checked 1 changesets with 1 changes to 1 files

  $ chmod -r .hg/store/data/a.i

  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  abort: Permission denied: $TESTTMP/t/.hg/store/data/a.i
  [255]

  $ chmod +r .hg/store/data/a.i

  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checked 1 changesets with 1 changes to 1 files

  $ chmod -w .hg/store/data/a.i

  $ echo barber > a
  $ hg commit -m "2"
  trouble committing a!
  abort: Permission denied: $TESTTMP/t/.hg/store/data/a.i
  [255]

  $ chmod -w .

  $ hg diff --nodates
  diff -r 2a18120dc1c9 a
  --- a/a
  +++ b/a
  @@ -1,1 +1,1 @@
  -foo
  +barber

  $ chmod +w .

  $ chmod +w .hg/store/data/a.i
  $ mkdir dir
  $ touch dir/a
  $ hg status
  M a
  ? dir/a
  $ chmod -rx dir

#if no-fsmonitor

(fsmonitor makes "hg status" avoid accessing to "dir")

  $ hg status
  dir: Permission denied
  M a

#endif

Reenable perm to allow deletion:

  $ chmod +rx dir

  $ cd ..