--- a/mercurial/util.py	Sun Mar 12 00:26:20 2017 -0800
+++ b/mercurial/util.py	Sun Mar 12 01:03:23 2017 -0800
@@ -1055,11 +1055,6 @@
 
     return check
 
-# Hardlinks are problematic on CIFS, do not allow hardlinks
-# until we find a way to work around it cleanly (issue4546).
-# This is a variable so extensions can opt-in to using them.
-allowhardlinks = False
-
 # a whilelist of known filesystems where hardlink works reliably
 _hardlinkfswhitelist = set([
     'btrfs',
@@ -1095,7 +1090,7 @@
         fstype = getattr(osutil, 'getfstype', lambda x: None)(destdir)
         if fstype not in _hardlinkfswhitelist:
             hardlink = False
-    if allowhardlinks and hardlink:
+    if hardlink:
         try:
             oslink(src, dest)
             return

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/test-hardlinks-whitelisted.t	Sun Mar 12 01:03:23 2017 -0800
@@ -0,0 +1,389 @@
+#require hardlink
+#require hardlink-whitelisted
+
+This test is similar to test-hardlinks.t, but will only run on some filesystems
+that we are sure to have known good hardlink supports (see issue4546 for an
+example where the filesystem claims hardlink support but is actually
+problematic).
+
+  $ cat > nlinks.py <<EOF
+  > import sys
+  > from mercurial import util
+  > for f in sorted(sys.stdin.readlines()):
+  >     f = f[:-1]
+  >     print util.nlinks(f), f
+  > EOF
+
+  $ nlinksdir()
+  > {
+  >     find $1 -type f | python $TESTTMP/nlinks.py
+  > }
+
+Some implementations of cp can't create hardlinks (replaces 'cp -al' on Linux):
+
+  $ cat > linkcp.py <<EOF
+  > from mercurial import util
+  > import sys
+  > util.copyfiles(sys.argv[1], sys.argv[2], hardlink=True)
+  > EOF
+
+  $ linkcp()
+  > {
+  >     python $TESTTMP/linkcp.py $1 $2
+  > }
+
+Prepare repo r1:
+
+  $ hg init r1
+  $ cd r1
+
+  $ echo c1 > f1
+  $ hg add f1
+  $ hg ci -m0
+
+  $ mkdir d1
+  $ cd d1
+  $ echo c2 > f2
+  $ hg add f2
+  $ hg ci -m1
+  $ cd ../..
+
+  $ nlinksdir r1/.hg/store
+  1 r1/.hg/store/00changelog.i
+  1 r1/.hg/store/00manifest.i
+  1 r1/.hg/store/data/d1/f2.i
+  1 r1/.hg/store/data/f1.i
+  1 r1/.hg/store/fncache
+  1 r1/.hg/store/phaseroots
+  1 r1/.hg/store/undo
+  1 r1/.hg/store/undo.backup.fncache
+  1 r1/.hg/store/undo.backupfiles
+  1 r1/.hg/store/undo.phaseroots
+
+
+Create hardlinked clone r2:
+
+  $ hg clone -U --debug r1 r2 --config progress.debug=true
+  linking: 1
+  linking: 2
+  linking: 3
+  linking: 4
+  linking: 5
+  linking: 6
+  linking: 7
+  linked 7 files
+
+Create non-hardlinked clone r3:
+
+  $ hg clone --pull r1 r3
+  requesting all changes
+  adding changesets
+  adding manifests
+  adding file changes
+  added 2 changesets with 2 changes to 2 files
+  updating to branch default
+  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
+
+
+Repos r1 and r2 should now contain hardlinked files:
+
+  $ nlinksdir r1/.hg/store
+  2 r1/.hg/store/00changelog.i
+  2 r1/.hg/store/00manifest.i
+  2 r1/.hg/store/data/d1/f2.i
+  2 r1/.hg/store/data/f1.i
+  2 r1/.hg/store/fncache
+  1 r1/.hg/store/phaseroots
+  1 r1/.hg/store/undo
+  1 r1/.hg/store/undo.backup.fncache
+  1 r1/.hg/store/undo.backupfiles
+  1 r1/.hg/store/undo.phaseroots
+
+  $ nlinksdir r2/.hg/store
+  2 r2/.hg/store/00changelog.i
+  2 r2/.hg/store/00manifest.i
+  2 r2/.hg/store/data/d1/f2.i
+  2 r2/.hg/store/data/f1.i
+  2 r2/.hg/store/fncache
+
+Repo r3 should not be hardlinked:
+
+  $ nlinksdir r3/.hg/store
+  1 r3/.hg/store/00changelog.i
+  1 r3/.hg/store/00manifest.i
+  1 r3/.hg/store/data/d1/f2.i
+  1 r3/.hg/store/data/f1.i
+  1 r3/.hg/store/fncache
+  1 r3/.hg/store/phaseroots
+  1 r3/.hg/store/undo
+  1 r3/.hg/store/undo.backupfiles
+  1 r3/.hg/store/undo.phaseroots
+
+
+Create a non-inlined filelog in r3:
+
+  $ cd r3/d1
+  >>> f = open('data1', 'wb')
+  >>> for x in range(10000):
+  ...     f.write("%s\n" % str(x))
+  >>> f.close()
+  $ for j in 0 1 2 3 4 5 6 7 8 9; do
+  >   cat data1 >> f2
+  >   hg commit -m$j
+  > done
+  $ cd ../..
+
+  $ nlinksdir r3/.hg/store
+  1 r3/.hg/store/00changelog.i
+  1 r3/.hg/store/00manifest.i
+  1 r3/.hg/store/data/d1/f2.d
+  1 r3/.hg/store/data/d1/f2.i
+  1 r3/.hg/store/data/f1.i
+  1 r3/.hg/store/fncache
+  1 r3/.hg/store/phaseroots
+  1 r3/.hg/store/undo
+  1 r3/.hg/store/undo.backup.fncache
+  1 r3/.hg/store/undo.backup.phaseroots
+  1 r3/.hg/store/undo.backupfiles
+  1 r3/.hg/store/undo.phaseroots
+
+Push to repo r1 should break up most hardlinks in r2:
+
+  $ hg -R r2 verify
+  checking changesets
+  checking manifests
+  crosschecking files in changesets and manifests
+  checking files
+  2 files, 2 changesets, 2 total revisions
+
+  $ cd r3
+  $ hg push
+  pushing to $TESTTMP/r1 (glob)
+  searching for changes
+  adding changesets
+  adding manifests
+  adding file changes
+  added 10 changesets with 10 changes to 1 files
+
+  $ cd ..
+
+  $ nlinksdir r2/.hg/store
+  1 r2/.hg/store/00changelog.i
+  1 r2/.hg/store/00manifest.i
+  1 r2/.hg/store/data/d1/f2.i
+  2 r2/.hg/store/data/f1.i
+  2 r2/.hg/store/fncache
+
+  $ hg -R r2 verify
+  checking changesets
+  checking manifests
+  crosschecking files in changesets and manifests
+  checking files
+  2 files, 2 changesets, 2 total revisions
+
+
+  $ cd r1
+  $ hg up
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+
+Committing a change to f1 in r1 must break up hardlink f1.i in r2:
+
+  $ echo c1c1 >> f1
+  $ hg ci -m00
+  $ cd ..
+
+  $ nlinksdir r2/.hg/store
+  1 r2/.hg/store/00changelog.i
+  1 r2/.hg/store/00manifest.i
+  1 r2/.hg/store/data/d1/f2.i
+  1 r2/.hg/store/data/f1.i
+  2 r2/.hg/store/fncache
+
+
+  $ cd r3
+  $ hg tip --template '{rev}:{node|short}\n'
+  11:a6451b6bc41f
+  $ echo bla > f1
+  $ hg ci -m1
+  $ cd ..
+
+Create hardlinked copy r4 of r3 (on Linux, we would call 'cp -al'):
+
+  $ linkcp r3 r4
+
+r4 has hardlinks in the working dir (not just inside .hg):
+
+  $ nlinksdir r4
+  2 r4/.hg/00changelog.i
+  2 r4/.hg/branch
+  2 r4/.hg/cache/branch2-served
+  2 r4/.hg/cache/checkisexec
+  3 r4/.hg/cache/checklink (?)
+  ? r4/.hg/cache/checklink-target (glob)
+  2 r4/.hg/cache/checknoexec
+  2 r4/.hg/cache/rbc-names-v1
+  2 r4/.hg/cache/rbc-revs-v1
+  2 r4/.hg/dirstate
+  2 r4/.hg/hgrc
+  2 r4/.hg/last-message.txt
+  2 r4/.hg/requires
+  2 r4/.hg/store/00changelog.i
+  2 r4/.hg/store/00manifest.i
+  2 r4/.hg/store/data/d1/f2.d
+  2 r4/.hg/store/data/d1/f2.i
+  2 r4/.hg/store/data/f1.i
+  2 r4/.hg/store/fncache
+  2 r4/.hg/store/phaseroots
+  2 r4/.hg/store/undo
+  2 r4/.hg/store/undo.backup.fncache
+  2 r4/.hg/store/undo.backup.phaseroots
+  2 r4/.hg/store/undo.backupfiles
+  2 r4/.hg/store/undo.phaseroots
+  4 r4/.hg/undo.backup.dirstate
+  2 r4/.hg/undo.bookmarks
+  2 r4/.hg/undo.branch
+  2 r4/.hg/undo.desc
+  4 r4/.hg/undo.dirstate
+  2 r4/d1/data1
+  2 r4/d1/f2
+  2 r4/f1
+
+Update back to revision 11 in r4 should break hardlink of file f1:
+
+  $ hg -R r4 up 11
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+
+  $ nlinksdir r4
+  2 r4/.hg/00changelog.i
+  1 r4/.hg/branch
+  2 r4/.hg/cache/branch2-served
+  2 r4/.hg/cache/checkisexec
+  2 r4/.hg/cache/checklink-target
+  2 r4/.hg/cache/checknoexec
+  2 r4/.hg/cache/rbc-names-v1
+  2 r4/.hg/cache/rbc-revs-v1
+  1 r4/.hg/dirstate
+  2 r4/.hg/hgrc
+  2 r4/.hg/last-message.txt
+  2 r4/.hg/requires
+  2 r4/.hg/store/00changelog.i
+  2 r4/.hg/store/00manifest.i
+  2 r4/.hg/store/data/d1/f2.d
+  2 r4/.hg/store/data/d1/f2.i
+  2 r4/.hg/store/data/f1.i
+  2 r4/.hg/store/fncache
+  2 r4/.hg/store/phaseroots
+  2 r4/.hg/store/undo
+  2 r4/.hg/store/undo.backup.fncache
+  2 r4/.hg/store/undo.backup.phaseroots
+  2 r4/.hg/store/undo.backupfiles
+  2 r4/.hg/store/undo.phaseroots
+  4 r4/.hg/undo.backup.dirstate
+  2 r4/.hg/undo.bookmarks
+  2 r4/.hg/undo.branch
+  2 r4/.hg/undo.desc
+  4 r4/.hg/undo.dirstate
+  2 r4/d1/data1
+  2 r4/d1/f2
+  1 r4/f1
+
+
+Test hardlinking outside hg:
+
+  $ mkdir x
+  $ echo foo > x/a
+
+  $ linkcp x y
+  $ echo bar >> y/a
+
+No diff if hardlink:
+
+  $ diff x/a y/a
+
+Test mq hardlinking:
+
+  $ echo "[extensions]" >> $HGRCPATH
+  $ echo "mq=" >> $HGRCPATH
+
+  $ hg init a
+  $ cd a
+
+  $ hg qimport -n foo - << EOF
+  > # HG changeset patch
+  > # Date 1 0
+  > diff -r 2588a8b53d66 a
+  > --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+  > +++ b/a	Wed Jul 23 15:54:29 2008 +0200
+  > @@ -0,0 +1,1 @@
+  > +a
+  > EOF
+  adding foo to series file
+
+  $ hg qpush
+  applying foo
+  now at: foo
+
+  $ cd ..
+  $ linkcp a b
+  $ cd b
+
+  $ hg qimport -n bar - << EOF
+  > # HG changeset patch
+  > # Date 2 0
+  > diff -r 2588a8b53d66 a
+  > --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+  > +++ b/b	Wed Jul 23 15:54:29 2008 +0200
+  > @@ -0,0 +1,1 @@
+  > +b
+  > EOF
+  adding bar to series file
+
+  $ hg qpush
+  applying bar
+  now at: bar
+
+  $ cat .hg/patches/status
+  430ed4828a74fa4047bc816a25500f7472ab4bfe:foo
+  4e7abb4840c46a910f6d7b4d3c3fc7e5209e684c:bar
+
+  $ cat .hg/patches/series
+  foo
+  bar
+
+  $ cat ../a/.hg/patches/status
+  430ed4828a74fa4047bc816a25500f7472ab4bfe:foo
+
+  $ cat ../a/.hg/patches/series
+  foo
+
+Test tags hardlinking:
+
+  $ hg qdel -r qbase:qtip
+  patch foo finalized without changeset message
+  patch bar finalized without changeset message
+
+  $ hg tag -l lfoo
+  $ hg tag foo
+
+  $ cd ..
+  $ linkcp b c
+  $ cd c
+
+  $ hg tag -l -r 0 lbar
+  $ hg tag -r 0 bar
+
+  $ cat .hgtags
+  4e7abb4840c46a910f6d7b4d3c3fc7e5209e684c foo
+  430ed4828a74fa4047bc816a25500f7472ab4bfe bar
+
+  $ cat .hg/localtags
+  4e7abb4840c46a910f6d7b4d3c3fc7e5209e684c lfoo
+  430ed4828a74fa4047bc816a25500f7472ab4bfe lbar
+
+  $ cat ../b/.hgtags
+  4e7abb4840c46a910f6d7b4d3c3fc7e5209e684c foo
+
+  $ cat ../b/.hg/localtags
+  4e7abb4840c46a910f6d7b4d3c3fc7e5209e684c lfoo
+
+  $ cd ..

--- a/tests/test-hardlinks.t	Sun Mar 12 00:26:20 2017 -0800
+++ b/tests/test-hardlinks.t	Sun Mar 12 01:03:23 2017 -0800
@@ -166,7 +166,7 @@
   1 r2/.hg/store/00manifest.i
   1 r2/.hg/store/data/d1/f2.i
   2 r2/.hg/store/data/f1.i
-  1 r2/.hg/store/fncache
+  [12] r2/\.hg/store/fncache (re)
 
   $ hg -R r2 verify
   checking changesets
@@ -191,7 +191,7 @@
   1 r2/.hg/store/00manifest.i
   1 r2/.hg/store/data/d1/f2.i
   1 r2/.hg/store/data/f1.i
-  1 r2/.hg/store/fncache
+  [12] r2/\.hg/store/fncache (re)
 
 
   $ cd r3
@@ -233,11 +233,11 @@
   2 r4/.hg/store/undo.backup.phaseroots
   2 r4/.hg/store/undo.backupfiles
   2 r4/.hg/store/undo.phaseroots
-  2 r4/.hg/undo.backup.dirstate
+  [24] r4/\.hg/undo\.backup\.dirstate (re)
   2 r4/.hg/undo.bookmarks
   2 r4/.hg/undo.branch
   2 r4/.hg/undo.desc
-  2 r4/.hg/undo.dirstate
+  [24] r4/\.hg/undo\.dirstate (re)
   2 r4/d1/data1
   2 r4/d1/f2
   2 r4/f1
@@ -272,11 +272,11 @@
   2 r4/.hg/store/undo.backup.phaseroots
   2 r4/.hg/store/undo.backupfiles
   2 r4/.hg/store/undo.phaseroots
-  2 r4/.hg/undo.backup.dirstate
+  [24] r4/\.hg/undo\.backup\.dirstate (re)
   2 r4/.hg/undo.bookmarks
   2 r4/.hg/undo.branch
   2 r4/.hg/undo.desc
-  2 r4/.hg/undo.dirstate
+  [24] r4/\.hg/undo\.dirstate (re)
   2 r4/d1/data1
   2 r4/d1/f2
   1 r4/f1