[PATCH STABLE v2] chmod: create a new file when flags are set on a hardlinked file

[Augie Fackler]

On Wed, May 03, 2017 at 11:58:17PM -0700, Gregory Szorc wrote:
> On Wed, May 3, 2017 at 2:36 AM, Koen Van Hoof <koen.van_hoof at nokia.com>
> wrote:
>
> > # HG changeset patch
> > # User Koen Van Hoof <koen.van_hoof at nokia.com>
> > # Date 1493215522 -7200
> > #      Wed Apr 26 16:05:22 2017 +0200
> > # Branch stable
> > # Node ID 04b33b356260d9d4c27f8cd223c7e5446a51ac48
> > # Parent  2de67783dd31c66be1677aa443b95eabb0129a75
> > chmod: create a new file when flags are set on a hardlinked file
> >
> > For performance reasons we have several repositories where the files in
> > the working
> > directory of 1 repo are hardlinks to the files of the other repo
> > When an update in one repo results in a chmod of a such a file, the
> > hardlink
> > has to be deleted and replaced by a regular file to make sure that the
> > change
> > does not happen in the other repo
> >
> > diff --git a/mercurial/posix.py b/mercurial/posix.py
> > --- a/mercurial/posix.py
> > +++ b/mercurial/posix.py
> > @@ -98,7 +98,8 @@ def isexec(f):
> >      return (os.lstat(f).st_mode & 0o100 != 0)
> >
> >  def setflags(f, l, x):
> > -    s = os.lstat(f).st_mode
> > +    st = os.lstat(f)
> > +    s = st.st_mode
> >      if l:
> >          if not stat.S_ISLNK(s):
> >              # switch file to link
> > @@ -124,6 +125,14 @@ def setflags(f, l, x):
> >          fp.close()
> >          s = 0o666 & ~umask # avoid restatting for chmod
> >
> > +    if st.st_nlink > 1: # the file is a hardlink, break the hardlink
> > +        fpin = open(f,"r")
> > +        unlink(f)
> > +        fpout = open(f, "w")
> > +        fpout.write(fpin.read())
> > +        fpin.close()
> > +        fpout.close()
> > +
> >
>
> I'll let someone else comment on the semantics of the change. But this
> should use context managers so file descriptors aren't leaked [until next
> garbage collection] in case of an exception.

I'm generally okay with the semantics of the patch - it was surprising
to me as a long-standing source control hacker that this
misbehaves. Sorry I didn't notice the context manager bit in the last
cycle.

(If anyone has objections to these semantics, please speak up.)

>
>
> >      sx = s & 0o100
> >      if x and not sx:
> >          # Turn on +x for every +r bit when making a file executable
> > @@ -132,6 +141,8 @@ def setflags(f, l, x):
> >      elif not x and sx:
> >          # Turn off all +x bits
> >          os.chmod(f, s & 0o666)
> > +    elif st.st_nlink > 1: # new file still needs its stat to be copied
> > +        os.chmod(f, s)
> >
> >  def copymode(src, dst, mode=None):
> >      '''Copy the file mode from the file at path src to dst.
> > diff --git a/tests/test-hardlinks.t b/tests/test-hardlinks.t
> > --- a/tests/test-hardlinks.t
> > +++ b/tests/test-hardlinks.t
> > @@ -193,11 +193,18 @@ Committing a change to f1 in r1 must bre
> >    1 r2/.hg/store/data/f1.i
> >    [12] r2/\.hg/store/fncache (re)
> >
> > +Create a file which exec permissions we will change
> > +  $ cd r3
> > +  $ echo "echo hello world" > f3
> > +  $ hg add f3
> > +  $ hg ci -mf3
> > +  $ cd ..
> >
> >    $ cd r3
> >    $ hg tip --template '{rev}:{node|short}\n'
> > -  11:a6451b6bc41f
> > +  12:d3b77733a28a
> >    $ echo bla > f1
> > +  $ chmod +x f3
> >    $ hg ci -m1
> >    $ cd ..
> >
> > @@ -226,6 +233,7 @@ r4 has hardlinks in the working dir (not
> >    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/data/f3.i
> >    2 r4/.hg/store/fncache
> >    2 r4/.hg/store/phaseroots
> >    2 r4/.hg/store/undo
> > @@ -241,11 +249,12 @@ r4 has hardlinks in the working dir (not
> >    2 r4/d1/data1
> >    2 r4/d1/f2
> >    2 r4/f1
> > +  2 r4/f3
> >
> > -Update back to revision 11 in r4 should break hardlink of file f1:
> > +Update back to revision 12 in r4 should break hardlink of file f1 and f3:
> >
> > -  $ hg -R r4 up 11
> > -  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
> > +  $ hg -R r4 up 12
> > +  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
> >
> >    $ nlinksdir r4
> >    2 r4/.hg/00changelog.i
> > @@ -265,6 +274,7 @@ Update back to revision 11 in r4 should
> >    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/data/f3.i
> >    2 r4/.hg/store/fncache
> >    2 r4/.hg/store/phaseroots
> >    2 r4/.hg/store/undo
> > @@ -280,6 +290,7 @@ Update back to revision 11 in r4 should
> >    2 r4/d1/data1
> >    2 r4/d1/f2
> >    1 r4/f1
> > +  1 r4/f3
> >
> >
> >  Test hardlinking outside hg:
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> >

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