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

mercurial/repair.py

@@ -1,358 +1,359
 # repair.py - functions for repository repair for mercurial
 #
 # Copyright 2005, 2006 Chris Mason <[e-mail]>
 # Copyright 2007 Matt Mackall
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from __future__ import absolute_import
 
 import errno
 import hashlib
 
 from .i18n import _
 from .node import short
 from . import (
     bundle2,
     changegroup,
     error,
     exchange,
     obsolete,
     util,
 )
 
 def _bundle(repo, bases, heads, node, suffix, compress=True):
     """create a bundle with the specified revisions as a backup"""
     cgversion = changegroup.safeversion(repo)
 
     cg = changegroup.changegroupsubset(repo, bases, heads, 'strip',
                                        version=cgversion)
     backupdir = "strip-backup"
     vfs = repo.vfs
     if not vfs.isdir(backupdir):
         vfs.mkdir(backupdir)
 
     # Include a hash of all the nodes in the filename for uniqueness
     allcommits = repo.set('%ln::%ln', bases, heads)
     allhashes = sorted(c.hex() for c in allcommits)
     totalhash = hashlib.sha1(''.join(allhashes)).hexdigest()
     name = "%s/%s-%s-%s.hg" % (backupdir, short(node), totalhash[:8], suffix)
 
     comp = None
     if cgversion != '01':
         bundletype = "HG20"
         if compress:
             comp = 'BZ'
     elif compress:
         bundletype = "HG10BZ"
     else:
         bundletype = "HG10UN"
     return bundle2.writebundle(repo.ui, cg, name, bundletype, vfs,
                                    compression=comp)
 
 def _collectfiles(repo, striprev):
     """find out the filelogs affected by the strip"""
     files = set()
 
     for x in xrange(striprev, len(repo)):
         files.update(repo[x].files())
 
     return sorted(files)
 
 def _collectbrokencsets(repo, files, striprev):
     """return the changesets which will be broken by the truncation"""
     s = set()
     def collectone(revlog):
         _, brokenset = revlog.getstrippoint(striprev)
         s.update([revlog.linkrev(r) for r in brokenset])
 
     collectone(repo.manifest)
     for fname in files:
         collectone(repo.file(fname))
 
     return s
 
 def strip(ui, repo, nodelist, backup=True, topic='backup'):
     # This function operates within a transaction of its own, but does
     # not take any lock on the repo.
     # Simple way to maintain backwards compatibility for this
     # argument.
     if backup in ['none', 'strip']:
         backup = False
 
     repo = repo.unfiltered()
     repo.destroying()
 
     cl = repo.changelog
     # TODO handle undo of merge sets
     if isinstance(nodelist, str):
         nodelist = [nodelist]
     striplist = [cl.rev(node) for node in nodelist]
     striprev = min(striplist)
 
     # Some revisions with rev > striprev may not be descendants of striprev.
     # We have to find these revisions and put them in a bundle, so that
     # we can restore them after the truncations.
     # To create the bundle we use repo.changegroupsubset which requires
     # the list of heads and bases of the set of interesting revisions.
     # (head = revision in the set that has no descendant in the set;
     #  base = revision in the set that has no ancestor in the set)
     tostrip = set(striplist)
     for rev in striplist:
         for desc in cl.descendants([rev]):
             tostrip.add(desc)
 
     files = _collectfiles(repo, striprev)
     saverevs = _collectbrokencsets(repo, files, striprev)
 
     # compute heads
     saveheads = set(saverevs)
     for r in xrange(striprev + 1, len(cl)):
         if r not in tostrip:
             saverevs.add(r)
             saveheads.difference_update(cl.parentrevs(r))
             saveheads.add(r)
     saveheads = [cl.node(r) for r in saveheads]
 
     # compute base nodes
     if saverevs:
         descendants = set(cl.descendants(saverevs))
         saverevs.difference_update(descendants)
     savebases = [cl.node(r) for r in saverevs]
     stripbases = [cl.node(r) for r in tostrip]
 
     # For a set s, max(parents(s) - s) is the same as max(heads(::s - s)), but
     # is much faster
     newbmtarget = repo.revs('max(parents(%ld) - (%ld))', tostrip, tostrip)
     if newbmtarget:
         newbmtarget = repo[newbmtarget.first()].node()
     else:
         newbmtarget = '.'
 
     bm = repo._bookmarks
     updatebm = []
     for m in bm:
         rev = repo[bm[m]].rev()
         if rev in tostrip:
             updatebm.append(m)
 
     # create a changegroup for all the branches we need to keep
     backupfile = None
     vfs = repo.vfs
     node = nodelist[-1]
     if backup:
         backupfile = _bundle(repo, stripbases, cl.heads(), node, topic)
         repo.ui.status(_("saved backup bundle to %s\n") %
                        vfs.join(backupfile))
         repo.ui.log("backupbundle", "saved backup bundle to %s\n",
                     vfs.join(backupfile))
     tmpbundlefile = None
     if saveheads:
         # do not compress temporary bundle if we remove it from disk later
         tmpbundlefile = _bundle(repo, savebases, saveheads, node, 'temp',
                             compress=False)
 
     mfst = repo.manifest
 
     curtr = repo.currenttransaction()
     if curtr is not None:
         del curtr  # avoid carrying reference to transaction for nothing
         msg = _('programming error: cannot strip from inside a transaction')
         raise error.Abort(msg, hint=_('contact your extension maintainer'))
 
     try:
         with repo.transaction("strip") as tr:
             offset = len(tr.entries)
 
             tr.startgroup()
             cl.strip(striprev, tr)
             mfst.strip(striprev, tr)
             if 'treemanifest' in repo.requirements: # safe but unnecessary
                                                     # otherwise
                 for unencoded, encoded, size in repo.store.datafiles():
                     if (unencoded.startswith('meta/') and
                         unencoded.endswith('00manifest.i')):
                         dir = unencoded[5:-12]
                         repo.manifest.dirlog(dir).strip(striprev, tr)
             for fn in files:
                 repo.file(fn).strip(striprev, tr)
             tr.endgroup()
 
             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)
 
         if tmpbundlefile:
             ui.note(_("adding branch\n"))
             f = vfs.open(tmpbundlefile, "rb")
             gen = exchange.readbundle(ui, f, tmpbundlefile, vfs)
             if not repo.ui.verbose:
                 # silence internal shuffling chatter
                 repo.ui.pushbuffer()
             if isinstance(gen, bundle2.unbundle20):
                 with repo.transaction('strip') as tr:
                     tr.hookargs = {'source': 'strip',
                                    'url': 'bundle:' + vfs.join(tmpbundlefile)}
                     bundle2.applybundle(repo, gen, tr, source='strip',
                                         url='bundle:' + vfs.join(tmpbundlefile))
             else:
                 gen.apply(repo, 'strip', 'bundle:' + vfs.join(tmpbundlefile),
                           True)
             if not repo.ui.verbose:
                 repo.ui.popbuffer()
             f.close()
         repo._phasecache.invalidate()
 
         for m in updatebm:
             bm[m] = repo[newbmtarget].node()
         lock = tr = None
         try:
             lock = repo.lock()
             tr = repo.transaction('repair')
             bm.recordchange(tr)
             tr.close()
         finally:
             tr.release()
             lock.release()
 
         # remove undo files
         for undovfs, undofile in repo.undofiles():
             try:
                 undovfs.unlink(undofile)
             except OSError as e:
                 if e.errno != errno.ENOENT:
                     ui.warn(_('error removing %s: %s\n') %
                             (undovfs.join(undofile), str(e)))
 
     except: # re-raises
         if backupfile:
             ui.warn(_("strip failed, backup bundle stored in '%s'\n")
                     % vfs.join(backupfile))
         if tmpbundlefile:
             ui.warn(_("strip failed, unrecovered changes stored in '%s'\n")
                     % vfs.join(tmpbundlefile))
             ui.warn(_("(fix the problem, then recover the changesets with "
                       "\"hg unbundle '%s'\")\n") % vfs.join(tmpbundlefile))
         raise
     else:
         if tmpbundlefile:
             # Remove temporary bundle only if there were no exceptions
             vfs.unlink(tmpbundlefile)
 
     repo.destroyed()
 
 def rebuildfncache(ui, repo):
     """Rebuilds the fncache file from repo history.
 
     Missing entries will be added. Extra entries will be removed.
     """
     repo = repo.unfiltered()
 
     if 'fncache' not in repo.requirements:
         ui.warn(_('(not rebuilding fncache because repository does not '
                   'support fncache)\n'))
         return
 
     with repo.lock():
         fnc = repo.store.fncache
         # Trigger load of fncache.
         if 'irrelevant' in fnc:
             pass
 
         oldentries = set(fnc.entries)
         newentries = set()
         seenfiles = set()
 
         repolen = len(repo)
         for rev in repo:
             ui.progress(_('rebuilding'), rev, total=repolen,
                         unit=_('changesets'))
 
             ctx = repo[rev]
             for f in ctx.files():
                 # This is to minimize I/O.
                 if f in seenfiles:
                     continue
                 seenfiles.add(f)
 
                 i = 'data/%s.i' % f
                 d = 'data/%s.d' % f
 
                 if repo.store._exists(i):
                     newentries.add(i)
                 if repo.store._exists(d):
                     newentries.add(d)
 
         ui.progress(_('rebuilding'), None)
 
         if 'treemanifest' in repo.requirements: # safe but unnecessary otherwise
             for dir in util.dirs(seenfiles):
                 i = 'meta/%s/00manifest.i' % dir
                 d = 'meta/%s/00manifest.d' % dir
 
                 if repo.store._exists(i):
                     newentries.add(i)
                 if repo.store._exists(d):
                     newentries.add(d)
 
         addcount = len(newentries - oldentries)
         removecount = len(oldentries - newentries)
         for p in sorted(oldentries - newentries):
             ui.write(_('removing %s\n') % p)
         for p in sorted(newentries - oldentries):
             ui.write(_('adding %s\n') % p)
 
         if addcount or removecount:
             ui.write(_('%d items added, %d removed from fncache\n') %
                      (addcount, removecount))
             fnc.entries = newentries
             fnc._dirty = True
 
             with repo.transaction('fncache') as tr:
                 fnc.write(tr)
         else:
             ui.write(_('fncache already up to date\n'))
 
 def stripbmrevset(repo, mark):
     """
     The revset to strip when strip is called with -B mark
 
     Needs to live here so extensions can use it and wrap it even when strip is
     not enabled or not present on a box.
     """
     return repo.revs("ancestors(bookmark(%s)) - "
                      "ancestors(head() and not bookmark(%s)) - "
                      "ancestors(bookmark() and not bookmark(%s))",
                      mark, mark, mark)
 
 def deleteobsmarkers(obsstore, indices):
     """Delete some obsmarkers from obsstore and return how many were deleted
 
     'indices' is a list of ints which are the indices
     of the markers to be deleted.
 
     Every invocation of this function completely rewrites the obsstore file,
     skipping the markers we want to be removed. The new temporary file is
     created, remaining markers are written there and on .close() this file
     gets atomically renamed to obsstore, thus guaranteeing consistency."""
     if not indices:
         # we don't want to rewrite the obsstore with the same content
         return
 
     left = []
     current = obsstore._all
     n = 0
     for i, m in enumerate(current):
         if i in indices:
             n += 1
             continue
         left.append(m)
 
     newobsstorefile = obsstore.svfs('obsstore', 'w', atomictemp=True)
     for bytes in obsolete.encodemarkers(left, True, obsstore._version):
         newobsstorefile.write(bytes)
     newobsstorefile.close()
     return n