Subject: Re: [RFC PATCH v3 1/5] clone: test for our behavior on odd objects/* content

From: Matheus Tavares <[email-masked]>
Date: Wed, 13 Mar 2019 00:17:47 -0300

Hi, Ævar

First of all, I must apologize for my very late reply. I just got back 
from a trip and only now have been able to look again at this series.

On Fri, Mar 1, 2019 at 10:49 AM Ævar Arnfjörð Bjarmason 
<[email-masked]> wrote:
 >
 >
 > On Thu, Feb 28 2019, Matheus Tavares Bernardino wrote:
 >
 > > Hi, Ævar
 > >
 > > I'm finishing the required changes in this series to send a v4, but
 > > when submitting to travis ci, I got some errors on the
 > > t5604-clone-reference test:
 > > https://travis-ci.org/MatheusBernardino/git/builds/500007587
 >
 > I don't have access to an OSX box, but could reproduce the failure on
 > NetBSD.
 >
 > It's because there link() when faced with a symlink behaves
 > differently. On GNU/Linux link()-ing a symlink will produce another
 > symlink like it, on NetBSD (and presumably OSX) doing that will produce
 > a hardlink to the file the existing symlink points to.

Hm, interesting. I installed NetBSD here and played with it a little: It 
seems that the inconsistency comes from the fact that link() follows 
symlinks on NetBSD but not on Linux. i.e., if you have a file "C" 
link()-ed to a file "B" which, in turn, is a symlink to a file "A", 
running "ls -li A B C" we can see that:
- On linux, C points to B's inode
- On NetBSD, C points to A's inode

 > I've pushed out a version of mine here which you might want to pull in:
 > https://github.com/git/git/compare/master...avar:clone-dir-iterator-3
 >
 > I.e. this whole thing is silly, but just preserving the notion that
 > we're not going to introduce behavior changes as we're refactoring.
 >
 > So it adds a commit right after the tests I added to detect this case,
 > and use symlink() or link() as appropriate instead of link().

I think this still modifies [a little] the current behaviour, since 
symlink() will make dest->buf point to a new inode (which will be a 
symlink just as src->buf, but on a different inode) while the current 
behaviour, on Linux, is to have dest->buf being a hardlink to src->buf 
(same inode). I don't know if this sentence got too confuse, but what I 
meant is that symlink() will make a symlink at dest->buf while link(), 
on linux, will make a hardlink to the given symlink.

 > There's then a commit at the end you might want to squash in that
 > reproduces this behavior on top of your iterator refactoring.
 >
 > Of course the DIR_ITERATOR_FOLLOW_SYMLINKS flag at this point is rather
 > silly. We're telling it to stat(), and then end up needing both stat()
 > and lstat() data.
 >
 > I'm starting to think that this interface which previously only had one
 > caller, but now has two exists at the wrong abstraction level. I.e. it
 > itself needs to call lstat(). Seems sensible to always do that and leave
 > it to the caller to call stat() if they need, as I believe Duy pointed
 > out.

I see what you mean, but if the caller needs to call stat() itself, in 
the occurrence of a symlink to a directory, it would have to start a new 
directory iteration upon the symlinked dir and its subdirectories (if it 
wants to follow symlinks). This approach could became a little messy, 
IMHO. And just by calling stat() at dir-iterator we already get the 
symlinked directories iterated "for free", without having to modify 
anything else in the code. So I still think it is a good idea to have 
the DIR_ITERATOR_FOLLOW_SYMLINKS flag at dir-iterator, making it call 
stat() instead of lstat().

 > Also noticed that dir-iterator.h still has a comment to the effect
 > that it'll call "lstat()", even though we now have a "stat() or
 > lstat()?" flag.

Thanks for noticing it, I will fix it in v4.

 > > On Tue, Feb 26, 2019 at 9:28 AM Ævar Arnfjörð Bjarmason
 > > <[email-masked]> wrote:
 > >>
 > >> Add tests for what happens when we locally clone .git/objects
 > >> directories where some of the loose objects or packs are symlinked, or
 > >> when when there's unknown files there.
 > >>
 > >> I'm bending over backwards here to avoid a SHA1 dependency. See [1]
 > >> for an earlier and simpler version that hardcoded a SHA-1s.
 > >>
 > >> This behavior has been the same for a *long* time, but hasn't been
 > >> tested for.
 > >>
 > >> There's a good post-hoc argument to be made for copying over unknown
 > >> things, e.g. I'd like a git version that doesn't know about the
 > >> commit-graph to copy it under "clone --local" so a newer git version
 > >> can make use of it.
 > >>
 > >> But the behavior showed where with symlinks seems pretty
 > >> random. E.g. if "pack" is a symlink we end up with two copies of the
 > >> contents, and only transfer some symlinks as-is.
 > >>
 > >> In follow-up commits we'll look at changing some of this behavior, but
 > >> for now let's just assert it as-is so we'll notice what we'll change
 > >> later.
 > >>
 > >> 1. 
https://public-inbox.org/git/[email-masked]/
 > >>
 > >> Signed-off-by: Ævar Arnfjörð Bjarmason <[email-masked]>
 > >> ---
 > >>  t/t5604-clone-reference.sh | 142 
+++++++++++++++++++++++++++++++++++++
 > >>  1 file changed, 142 insertions(+)
 > >>
 > >> diff --git a/t/t5604-clone-reference.sh b/t/t5604-clone-reference.sh
 > >> index 4320082b1b..cb0dc22d14 100755
 > >> --- a/t/t5604-clone-reference.sh
 > >> +++ b/t/t5604-clone-reference.sh
 > >> @@ -221,4 +221,146 @@ test_expect_success 'clone, dissociate from 
alternates' '
 > >>         ( cd C && git fsck )
 > >>  '
 > >>
 > >> +test_expect_success 'setup repo with garbage in objects/*' '
 > >> +       git init S &&
 > >> +       (
 > >> +               cd S &&
 > >> +               test_commit A &&
 > >> +
 > >> +               cd .git/objects &&
 > >> +               >.some-hidden-file &&
 > >> +               >some-file &&
 > >> +               mkdir .some-hidden-dir &&
 > >> +               >.some-hidden-dir/some-file &&
 > >> +               >.some-hidden-dir/.some-dot-file &&
 > >> +               mkdir some-dir &&
 > >> +               >some-dir/some-file &&
 > >> +               >some-dir/.some-dot-file
 > >> +       )
 > >> +'
 > >> +
 > >> +test_expect_success 'clone a repo with garbage in objects/*' '
 > >> +       for option in --local --no-hardlinks --shared --dissociate
 > >> +       do
 > >> +               git clone $option S S$option || return 1 &&
 > >> +               git -C S$option fsck || return 1
 > >> +       done &&
 > >> +       find S-* -name "*some*" | sort >actual &&
 > >> +       cat >expected <<-EOF &&
 > >> +       S--dissociate/.git/objects/.some-hidden-file
 > >> +       S--dissociate/.git/objects/some-dir
 > >> +       S--dissociate/.git/objects/some-dir/.some-dot-file
 > >> +       S--dissociate/.git/objects/some-dir/some-file
 > >> +       S--dissociate/.git/objects/some-file
 > >> +       S--local/.git/objects/.some-hidden-file
 > >> +       S--local/.git/objects/some-dir
 > >> +       S--local/.git/objects/some-dir/.some-dot-file
 > >> +       S--local/.git/objects/some-dir/some-file
 > >> +       S--local/.git/objects/some-file
 > >> +       S--no-hardlinks/.git/objects/.some-hidden-file
 > >> +       S--no-hardlinks/.git/objects/some-dir
 > >> +       S--no-hardlinks/.git/objects/some-dir/.some-dot-file
 > >> +       S--no-hardlinks/.git/objects/some-dir/some-file
 > >> +       S--no-hardlinks/.git/objects/some-file
 > >> +       EOF
 > >> +       test_cmp expected actual
 > >> +'
 > >> +
 > >> +test_expect_success SYMLINKS 'setup repo with manually symlinked 
objects/*' '
 > >> +       git init T &&
 > >> +       (
 > >> +               cd T &&
 > >> +               test_commit A &&
 > >> +               git gc &&
 > >> +               (
 > >> +                       cd .git/objects &&
 > >> +                       mv pack packs &&
 > >> +                       ln -s packs pack
 > >> +               ) &&
 > >> +               test_commit B &&
 > >> +               (
 > >> +                       cd .git/objects &&
 > >> +                       find ?? -type d >loose-dirs &&
 > >> +                       last_loose=$(tail -n 1 loose-dirs) &&
 > >> +                       mv $last_loose a-loose-dir &&
 > >> +                       ln -s a-loose-dir $last_loose &&
 > >> +                       first_loose=$(head -n 1 loose-dirs) &&
 > >> +                       (
 > >> +                               cd $first_loose &&
 > >> +                               obj=$(ls *) &&
 > >> +                               mv $obj ../an-object &&
 > >> +                               ln -s ../an-object $obj
 > >> +                       ) &&
 > >> +                       find . -type f | sort 
 >../../../T.objects-files.raw &&
 > >> +                       find . -type l | sort 
 >../../../T.objects-links.raw
 > >> +               )
 > >> +       ) &&
 > >> +       git -C T fsck &&
 > >> +       git -C T rev-list --all --objects >T.objects
 > >> +'
 > >> +
 > >> +
 > >> +test_expect_success SYMLINKS 'clone repo with symlinked objects/*' '
 > >> +       for option in --local --no-hardlinks --shared --dissociate
 > >> +       do
 > >> +               git clone $option T T$option || return 1 &&
 > >> +               git -C T$option fsck || return 1 &&
 > >> +               git -C T$option rev-list --all --objects 
 >T$option.objects &&
 > >> +               test_cmp T.objects T$option.objects &&
 > >> +               (
 > >> +                       cd T$option/.git/objects &&
 > >> +                       find . -type f | sort 
 >../../../T$option.objects-files.raw &&
 > >> +                       find . -type l | sort 
 >../../../T$option.objects-links.raw
 > >> +               )
 > >> +       done &&
 > >> +
 > >> +       for raw in $(ls T*.raw)
 > >> +       do
 > >> +               sed -e "s!/..\$!/X!; s!/../!/Y/!; 
s![0-9a-f]\{38,\}!Z!" <$raw >$raw.de-sha || return 1
 > >> +       done &&
 > >> +
 > >> +       cat >expected-files <<-EOF &&
 > >> +       ./Y/Z
 > >> +       ./a-loose-dir/Z
 > >> +       ./an-object
 > >> +       ./Y/Z
 > >> +       ./info/packs
 > >> +       ./loose-dirs
 > >> +       ./pack/pack-Z.idx
 > >> +       ./pack/pack-Z.pack
 > >> +       ./packs/pack-Z.idx
 > >> +       ./packs/pack-Z.pack
 > >> +       EOF
 > >> +       cat >expected-links <<-EOF &&
 > >> +       ./Y/Z
 > >> +       EOF
 > >> +       for option in --local --dissociate
 > >> +       do
 > >> +               test_cmp expected-files 
T$option.objects-files.raw.de-sha || return 1 &&
 > >> +               test_cmp expected-links 
T$option.objects-links.raw.de-sha || return 1
 > >> +       done &&
 > >> +
 > >> +       cat >expected-files <<-EOF &&
 > >> +       ./Y/Z
 > >> +       ./Y/Z
 > >> +       ./a-loose-dir/Z
 > >> +       ./an-object
 > >> +       ./Y/Z
 > >> +       ./info/packs
 > >> +       ./loose-dirs
 > >> +       ./pack/pack-Z.idx
 > >> +       ./pack/pack-Z.pack
 > >> +       ./packs/pack-Z.idx
 > >> +       ./packs/pack-Z.pack
 > >> +       EOF
 > >> +       test_cmp expected-files 
T--no-hardlinks.objects-files.raw.de-sha &&
 > >> +       test_must_be_empty T--no-hardlinks.objects-links.raw.de-sha &&
 > >> +
 > >> +       cat >expected-files <<-EOF &&
 > >> +       ./info/alternates
 > >> +       EOF
 > >> +       test_cmp expected-files T--shared.objects-files.raw &&
 > >> +       test_must_be_empty T--shared.objects-links.raw
 > >> +'
 > >> +
 > >>  test_done
 > >> --
 > >> 2.21.0.rc2.261.ga7da99ff1b
 > >>