RE: FW: [cygwin] Cygwin's git says "error: failed to read delta-pack base object"
- From
Jason Pyeron <jpyeron@pdinc.us>
- Date
- Dec 7, 2014, 01:33 UTC
- Message-ID
- <275080CE3B5A44D7A46B3DF0E55C33D4@black>
- In-Reply-To
- <F5116E3BF1974D039102426C8F6E3BED@black>
TLDR = Cygwin remote filesystem sometimes has strange failures -> workaround is to use rename, not link/unlink; see https://github.com/pdinc-oss/git/commit/5a36824ed01d4335148ca3846e75cc99c11650e2
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> -----Original Message----- > From: Jason Pyeron > Sent: Friday, December 05, 2014 10:30 > > > -----Original Message----- > > From: Jason Pyeron > > Sent: Thursday, December 04, 2014 16:34 > > > > > -----Original Message----- > > > From: brian m. carlson > > > Sent: Wednesday, December 03, 2014 19:55 > > > > > > On Wed, Dec 03, 2014 at 06:31:18PM -0500, Jason Pyeron wrote: > > > > I remember hitting this a while ago, but just gave up. > > > > > > > > It seems to be a problem for others too. > > > > > > > > Any ideas on how to debug this so it can be patched? > > > > > > > > -----Original Message----- > > > > From: Dave Lindbergh > > > > Sent: Wednesday, December 03, 2014 18:07 > > > > To: cygwin > > > > > > > > Aha - you're right. > > > > > > > > It works fine on a local NTFS volume. > > > > > > > > I get the error when I do it on Z:, which is mapped to a > > > network drive > > > > (on another Windows box). > > > > > > > > Is there a workaround? Why does this happen?
I have a really hacky workaround, commit 5a36824ed01d4335148ca3846e75cc99c11650e2 comments out the logic and forces a rename instead of link and unlink.
https://github.com/pdinc-oss/git/tree/cygwin-issue-remoteCIFS-rename
<snip/>
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> Pseudo code and observations
> ./sha1_file.c:write_loose_object(sha1)
> {
> filename=sha1_file_name(sha1)
> (fd,tmp_file)=create_tmpfile(filename)
> write_buffer(fd)
> close_sha1_file(fd)
> return move_temp_to_file(tmp_file, filename)
> }
>
> move_temp_to_file(tmpfile, filename)
> {
> // I am thinking about forcing renames to see if the problem
> exists then as well
> // if that "works" then a per repo config option allowing
> for forced renames
> if (OBJECT_CREATION_USES_RENAMES) goto try_rename
> else if link(tmpfile,filename)
> Dave has tested a build I made for him on 64 bit Cygwin and it works. I no longer have access to the environment I was having this problem in last February. I will try to investigate this further, but I am not hopeful, maybe Corinna will have luck on the issue. But I was in a secure corporate environment and I thought the host based security system (AV), coupled with the remote file system was causing the problem, namely files created are not available instantly.
I do think that we should have a config option for this, as most users who could encounter such a problem are not likely to be able (or allowed) to rebuild the git executable themselves.
<snip/>
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> > -----Original Message----- > > From: Corinna Vinschen > > Sent: Friday, December 05, 2014 6:35 > > To: cygwin@cygwin.com > <snip/> > > What I found in the strace is this: > > > > - Create file Z:\pic32mx-bmf\.git\objects\30\tmp_obj_YljwNZ > > > > - open file, write something, close file. > > > > - link (Z:\pic32mx-bmf\.git\objects\30\tmp_obj_YljwNZ, > > > > > Z:\pic32mx-bmf\.git\objects\30\0bdeb2fd209d24afb865584da10b78aa8fefc4) > > succeeds. > > > > - unlink (Z:\pic32mx-bmf\.git\objects\30\tmp_obj_YljwNZ) succeeds > > > > - Trying to open > > > > > Z:\pic32mx-bmf\.git\objects\30\0bdeb2fd209d24afb865584da10b78aa8fefc4 > > but the file doesn't exist and NtCreateFile fails with status > > 0xC0000034, STATUS_OBJECT_NAME_NOT_FOUND --> ENOENT. > > > > - Subsequent unlink (Z:\pic32mx-bmf\.git\objects\30) fails with a > > STATUS_DIRECTORY_NOT_EMPTY --> ENOTEMPTY. > > > > - git seems to be prepared for such a case, the parent process calls > > opendir/readdir on the directory. Enumerating the files in > > Z:\pic32mx-bmf\.git\objects\30 shows the entries ".", ".." and > > "0bdeb2fd209d24afb865584da10b78aa8fefc4". > > > > - Then git calls lstat on the file, which results in NtOpenFile > > returning status STATUS_OBJECT_NAME_NOT_FOUND again. > > > > - From a POSIX POV this means "somebody else" deleted the file, > > so the dir is empty now. Git tries to delete the directory again, > > which again results in STATUS_DIRECTORY_NOT_EMPTY --> ENOTEMPTY > > and, internally, a sharing violation which disallows to move the > > directory out of the way. > > > > This looks suspiciously like a bug in the remote filesystem. Link > > succeeded, so there are two links to the same file in the directory. > > Unlinking link 1 succeeds, so there's still one link to the > > file in the > > directory, but link 2 is inaccessible as if the file has > been deleted > > completely. Thus, a full POSIX git on this drive is broken. > > > > Can you please run > > > > /usr/lib/csih/getVolInfo /cygdrive/z > > > > and paste the output here? Maybe I can workaround this in the next > > Cygwin version.
Dave's response: https://www.cygwin.com/ml/cygwin/2014-12/msg00066.html
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