Hi Eric,
=== Short story ===
git-svn on Cygwin works well with svn+ssh://, but needs some fixes around
tempfile and/or subprocess handling for https:// - please help.
=== Long story ===
First the good news: git-svn on Cygwin seems to work just fine with
svn+ssh://... style Subversion URLs. I've been doing this for quite a
while now with various repos, never had issues: I can init, clone, fetch
rebase, dcommit just fine.
I'm looking for some help https:// access on Cygwin (Windows XP SP3
underneath; more version info at the end of the message).
I've debugged it a little, but am not sufficiently acquainted with the
git-svn Perl source to do changes myself; I hope I can describe the issue
well enough that you (or somebody else) can suggest code changes to
improve the experience.
0. PROBLEM/SYMPTOM:
login@mycomp ~/compnet2.gitsvn
$ git svn fetch
M file1
A file2
A file3
A file4
r15 = 70a56f818a057442e29161170e28c5df4b38a811 (git-svn)
Permission denied: Can't open
'/cygdrive/c/DOKUME~1/login/LOKALE~1/Temp/tempfile.tmp': Permission denied
at /usr/local/libexec/git-core/git-svn line 2540
which is, in my version:
2537 }
2538 $ed = SVN::Git::Fetcher->new($self);
2539 }
+ 2540 unless ($self->ra->gs_do_update($last_rev, $rev, $self,
$ed)) {
2541 die "SVN connection failed somewhere...\n";
2542 }
2543 $self->make_log_entry($rev, \@parents, $ed);
Apparently, we die when fetching a new revision for the 2nd time. I can
restart git svn fetch and it will pick up where it left off. It will make
progress, but is painful.
git svn rebase has the same issues. I haven't tested other operations such
as dcommit yet.
1. WORKAROUND for fetch/rebase:
while ! git svn fetch ; do : ; done
git svn rebase
2. A SHORT LOG OF FINDING THE CAUSE:
$ perl -d /usr/local/libexec/git-core/git-svn fetch
...
main::(/usr/local/libexec/git-core/git-svn:10):
10: $AUTHOR = 'Eric Wong [off-list ref]';
DB<1> c 2540
Git::SVN::do_fetch(/usr/local/libexec/git-core/git-svn:2540):
2540: unless ($self->ra->gs_do_update($last_rev, $rev, $self,
$ed)) {
DB<2> c 2540
...
r16 = d7829595222a013e703fe4377996984b52921789 (git-svn)
Git::SVN::do_fetch(/usr/local/libexec/git-core/git-svn:2540):
2540: unless ($self->ra->gs_do_update($last_rev, $rev, $self,
$ed)) {
Now watch this (we're immediately before the problem):
$ ls -l /cygdrive/c/DOKUME~1/login/LOKALE~1/Temp/
??????????? ? ? ? ? ? tempfile.tmp
$ ls -l /cygdrive/c/DOKUME~1/login/LOKALE~1/Temp/tempfile.tmp
ls: cannot access /cygdrive/c/DOKUME~1/login/LOKALE~1/Temp/tempfile.tmp:
No such file or directory
This zombie behaviour of trashing the file flags happens if Cygwin is
asked to unlink() a file to which there are still open handles. It can't
delete the file right away (due to the open handles), so it marks it
delete-on-close instead, which then happens when the process(es) terminate.
$ ~/Desktop/handle.exe tempfile.tmp
...
git.exe pid: 2236 62C:
C:\DOKUME~1\mandree\LOKALE~1\Temp\tempfile.tmp
git.exe pid: 5552 62C:
C:\DOKUME~1\mandree\LOKALE~1\Temp\tempfile.tmp
git-hash-object.exe pid: 5320 62C:
C:\DOKUME~1\mandree\LOKALE~1\Temp\tempfile.tmp
So we have three processes that have the file open. I cannot say if they
mean the same file, or a different one, but this is the problem.
Here's the pstree dump to help identify the users of this file, with
cmdline arguments:
perl,5660 -d -I... /usr/local/libexec/git-core/git-svn fetch
|-git,2236 --batch
|-git,5552 git-hash-object -w --stdin-paths
| `-git-hash-object,5320
`-git,1128 update-index -z --index-info
Let's continue in the Perl debugger and crash:
DB<3> c
Permission denied: Can't open
'/cygdrive/c/DOKUME~1/login/LOKALE~1/Temp/tempfile.tmp': Permission denied
at /usr/local/libexec/git-core/git-svn line 2540
Bottom line: the second time we hit this "unless
($self->ra->gs_do_update($last_rev, $rev, $self, $ed))" line, we die
because there are still processes that have the tempfile open and thus the
former unlink() on the tempfile.tmp couldn't become effective.
3. UNDERLYING CYGWIN LIMITATIONS
<http://wiki.osdev.org/Cygwin_Issues#unlink.28.29> documents now
(2009-04-23 16:15 UTC):
* unlink isn't atomic (as on other platforms also)
...
On cygwin unlink() is deferred to the end of the process, when unlink
fails because of locks or delete on close (ERROR_SHARING_VIOLATION).
* unlink a file and subsequent creation of a new file in the same location
is not supported.
* "delete on close" (unlinking an open file) is supported.
I can provide a short C program to demonstrate this behaviour.
4. FIX SUGGESTIONS AND QUESTIONS
Can we defer unlink()ing the tempfile until all handles to it are closed?
Can we let complete and wait for all processes that hold handles to the
tempfile.tmp file before attempting to create a new copy?
Can we use unique tempfile names (timestamps, counter, random number
generator) instead of the hardcoded "tempfile.tmp"? This is probably a
good idea anyways to evade symlink attacks.
Either should work to fix the issue.
I'm willing to test patches.
5. VERSION INFORMATION:
Cygwin:
CYGWIN_NT-5.1 balu 1.5.25(0.156/4/2) 2008-06-12 19:34 i686 Cygwin
Git:
git version 1.6.3.rc1.51.gea0b7
Subversion:
svn, version 1.6.1 (r37116)
compiled Apr 11 2009, 12:07:06
Copyright (C) 2000-2009 CollabNet.
Subversion is open source software, see http://subversion.tigris.org/
This product includes software developed by CollabNet
(http://www.Collab.Net/).
The following repository access (RA) modules are available:
* ra_neon : Module for accessing a repository via WebDAV protocol using
Neon.
- handles 'http' scheme
- handles 'https' scheme
* ra_svn : Module for accessing a repository using the svn network
protocol.
- with Cyrus SASL authentication
- handles 'svn' scheme
* ra_local : Module for accessing a repository on local disk.
- handles 'file' scheme
* ra_serf : Module for accessing a repository via WebDAV protocol using
serf.
- handles 'http' scheme
- handles 'https' scheme
Thanks for any efforts to help!
--
Matthias Andree
As a followup to my own message,
here's one more link to explain Cygwin/Windows limitations that seem to
break git-svn here:
http://markmail.org/message/4o4yk6b4u6e44wyh
Thanks in advance for any help offered with git-svn.
--
Matthias Andree
3. UNDERLYING CYGWIN LIMITATIONS
* unlink a file and subsequent creation of a new file in the same location
is not supported.
* "delete on close" (unlinking an open file) is supported.
These last two points are old information. I would first recommend that you
try running the new cygwin 1.7 (still in beta), where unlink() semantics have
been greatly improved (you can actually unlink() an in-use file and recreate a
new file by the same name while the old handle is still open).
http://cygwin.com/#beta-test
4. FIX SUGGESTIONS AND QUESTIONS
Can we defer unlink()ing the tempfile until all handles to it are closed?
Can we let complete and wait for all processes that hold handles to the
tempfile.tmp file before attempting to create a new copy?
Can we use unique tempfile names (timestamps, counter, random number
generator) instead of the hardcoded "tempfile.tmp"? This is probably a
good idea anyways to evade symlink attacks.
Although newer cygwin may fix your particular problem, this is not a bad
suggestion for msysgit, so I suspect someone may be bothered enough by this to
write a patch. I, however, will not be the one doing it.
--
Eric Blake
Am 23.04.2009, 19:58 Uhr, schrieb Eric Blake [off-list ref]:
quoted
Can we use unique tempfile names (timestamps, counter, random number
generator) instead of the hardcoded "tempfile.tmp"? This is probably a
good idea anyways to evade symlink attacks.
Although newer cygwin may fix your particular problem, this is not a bad
suggestion for msysgit, so I suspect someone may be bothered enough by
this to write a patch. I, however, will not be the one doing it.
Hi Eric,
thanks for the hints and pointers to Cygwin 1.7 beta, however I'd suggest
to make such changes upstream (i. e. in git.git) for the benefit of
everybody else.
It also looks to me as though minor changes in the actual baseline Git
code may be sufficient to get git-svn working on Cygwin 1.5 (stable)
already. I'd prefer such a minor intrusion to hacking away on forks. :-)
Otherwise I'd start looking at how git-svn handles https:// and svn+ssh://
methods differently from each other next week or so.
Looking forward to further insights.
--
Matthias Andree
Am 23.04.2009, 19:58 Uhr, schrieb Eric Blake [off-list ref]:
These last two points are old information. I would first recommend that
you try running the new cygwin 1.7 (still in beta), where unlink()
semantics have been greatly improved (you can actually unlink() an
in-use file and recreate a new file by the same name while the old
handle is still open).
http://cygwin.com/#beta-test
Indeed, with a fresh Cygwin 1.7 install, all this seems to work smoothly.
I'd rather not bet on Cygwin release dates though, and can't judge on
short notice what else will break with Cygwin 1.7... so I'd still
appreciate help with fixing git-svn on Cygwin 1.5.
--
Matthias Andree
From: Eric Wong <hidden> Date: 2016-06-15 22:46:39
Matthias Andree [off-list ref] wrote:
Hi Eric,
=== Short story ===
git-svn on Cygwin works well with svn+ssh://, but needs some fixes around
tempfile and/or subprocess handling for https:// - please help.
Hi Matthias,
Marcus Griep did a lot of work for more efficiently handling of
tempfiles in Git.pm a few months ago, so maybe he has more insight into
how things work...
git-svn used to use IO::File->new_tmpfile() which was much simpler and
probably less prone to portability problems, but cycled through inodes
too quickly for Marcus (and probably some other people).
Speaking only for myself and not other contributors:
I have no interest in dealing with crazy systems like Windows. Ever.
However, I'll gladly accept patches to make things work if they don't
break existing use cases.
Keep in mind that I'm an extremist. I dislike Windows (and some other
crazy software systems) to the point that I refuse to deal with them
even in paid contracts and employment.
--
Eric Wong
Am 23.04.2009, 21:03 Uhr, schrieb Eric Wong [off-list ref]:
Matthias Andree [off-list ref] wrote:
quoted
Hi Eric,
=== Short story ===
git-svn on Cygwin works well with svn+ssh://, but needs some fixes
around
tempfile and/or subprocess handling for https:// - please help.
Hi Matthias,
Marcus Griep did a lot of work for more efficiently handling of
tempfiles in Git.pm a few months ago, so maybe he has more insight into
how things work...
git-svn used to use IO::File->new_tmpfile() which was much simpler and
probably less prone to portability problems, but cycled through inodes
too quickly for Marcus (and probably some other people).
I debugged this a bit further, and the damage (i. e. removal of the
tempfile) apparently happens
in $pool->clear; in line 4355. I single-stepped it, and the
apr_pool_clear(...) is the culprit, it unlinks() the tempfile, making this
location unusable.
The temp file is generated when the Reporter object is created through
$self->do_update in line 4336.
It remains unclear to me who generates the non-unique filename (it's
...\Temp\tempfile.tmp for me), I've not found the code that generates the
file names.
Questions:
- How can I either make sure that the temporary file name for the reporter
gets either a unique name (near line 4336, through SVN::Ra...)
- or is that the temp file truncated, rather than deleted, near line 4355
(through SVN::Pool::clear)?
- Is there any way to influence how the SVN::Ra::Reporter obtains
temporary files?
I seem to be unable to trace this down to the actual functions, but then
again, my perlboot is rather holey...
Any help?
4132 package Git::SVN::Ra;
4133 use vars qw/@ISA $config_dir $_log_window_size/;
4134 use strict;
4135 use warnings;
4136 my ($ra_invalid, $can_do_switch, %ignored_err, $RA);
4137
....
4324 sub gs_do_update {
4325 my ($self, $rev_a, $rev_b, $gs, $editor) = @_;
4326 my $new = ($rev_a == $rev_b);
4327 my $path = $gs->{path};
4328
4329 if ($new && -e $gs->{index}) {
4330 unlink $gs->{index} or die
4331 "Couldn't unlink index: $gs->{index}: $!\n";
4332 }
4333 my $pool = SVN::Pool->new;
4334 $editor->set_path_strip($path);
4335 my (@pc) = split m#/#, $path;
: 4336 my $reporter = $self->do_update($rev_b, (@pc ? shift @pc :
''),
4337 1, $editor, $pool);
4338 my @lock = $SVN::Core::VERSION ge '1.2.0' ? (undef) : ();
4339
4340 # Since we can't rely on svn_ra_reparent being available,
we'll
4341 # just have to do some magic with set_path to make it so
4342 # we only want a partial path.
4343 my $sp = '';
4344 my $final = join('/', @pc);
4345 while (@pc) {
4346 $reporter->set_path($sp, $rev_b, 0, @lock, $pool);
4347 $sp .= '/' if length $sp;
4348 $sp .= shift @pc;
4349 }
4350 die "BUG: '$sp' != '$final'\n" if ($sp ne $final);
4351
4352 $reporter->set_path($sp, $rev_a, $new, @lock, $pool);
4353
4354 $reporter->finish_report($pool);
: 4355 $pool->clear;
4356 $editor->{git_commit_ok};
4357 }
--
Matthias Andree