Patchwork [8,of,9,V2] repair: open a file with checkambig=True to avoid file stat ambiguity

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Submitter Katsunori FUJIWARA
Date Sept. 22, 2016, 12:59 p.m.
Message ID <338febde64d5fe6a5aac.1474549167@feefifofum>
Download mbox | patch
Permalink /patch/16755/
State Accepted
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Katsunori FUJIWARA - Sept. 22, 2016, 12:59 p.m.
# HG changeset patch
# User FUJIWARA Katsunori <foozy@lares.dti.ne.jp>
# Date 1474548720 -32400
#      Thu Sep 22 21:52:00 2016 +0900
# Node ID 338febde64d5fe6a5aac79aff54741e201b5d88f
# Parent  5ec24143ad2e85bf1567d9af83df9fc5187f0a4e
repair: open a file with checkambig=True to avoid file stat ambiguity

Before this patch, if steps below occurs at "the same time in sec",
all of mtime, ctime and size are same between (1) and (3).

  1. append data to revlog-style file (and close transaction)
  2. discard appended data by truncation of strip
  3. append same size but different data to revlog-style file again

Therefore, cache validation doesn't work after (3) as expected.

To avoid such file stat ambiguity around truncation, this patch opens
a file with checkambig=True.

This patch also introduces "with" statement style, to ensure immediate
invocation of close() after truncation, because closing file is the
only trigger to check (and get rid of) file stat ambiguity.

This is a part of ExactCacheValidationPlan.

    https://www.mercurial-scm.org/wiki/ExactCacheValidationPlan

Patch

diff --git a/mercurial/repair.py b/mercurial/repair.py
--- a/mercurial/repair.py
+++ b/mercurial/repair.py
@@ -181,7 +181,8 @@  def strip(ui, repo, nodelist, backup=Tru
 
             for i in xrange(offset, len(tr.entries)):
                 file, troffset, ignore = tr.entries[i]
-                repo.svfs(file, 'a').truncate(troffset)
+                with repo.svfs(file, 'a', checkambig=True) as fp:
+                    fp.truncate(troffset)
                 if troffset == 0:
                     repo.store.markremoved(file)