Error adding 2+ files after init --shared with fscache

[stevekmcc]

• I was not able to find an open or closed issue matching what I'm seeing

Setup

• Which version of Git for Windows are you using? Is it 32-bit or 64-bit?

$ git --version --build-options

git version 2.30.2.windows.1
cpu: x86_64
built from commit: 37f0a4afad027cf030747a1ef45537ba86162960
sizeof-long: 4
sizeof-size_t: 8
shell-path: /bin/sh

• Which version of Windows are you running? Vista, 7, 8, 10? Is it 32-bit or 64-bit?

$ cmd.exe /c ver

Microsoft Windows [Version 10.0.19041.867] 64-bit

• What options did you set as part of the installation? Or did you choose the
  defaults?

All defaults:
> type "C:\Program Files\Git\etc\install-options.txt"

Editor Option: VIM
Custom Editor Path:
Default Branch Option:
Path Option: Cmd
SSH Option: OpenSSH
Tortoise Option: false
CURL Option: OpenSSL
CRLF Option: CRLFAlways
Bash Terminal Option: MinTTY
Git Pull Behavior Option: Merge
Use Credential Manager: Core
Performance Tweaks FSCache: Enabled
Enable Symlinks: Disabled
Enable Pseudo Console Support: Disabled

• Any other interesting things about your environment that might be related
  to the issue you're seeing?

Seems independent of machine or disk type (SSD, HDD, external USB HDD)

Details

• Which terminal/shell are you running Git from? e.g Bash/CMD/PowerShell/other

CMD

• What commands did you run to trigger this issue? If you can provide a
  Minimal, Complete, and Verifiable example
  this will help us understand the issue.

git init --shared
echo x>x
echo y>y
git add -A

• What did you expect to occur after running these commands?

The two files are added with no errors

• What actually happened instead?

error: unable to create temporary file: No such file or directory
error: y: failed to insert into database
error: unable to index file 'y'
fatal: adding files failed

• If the problem was occurring with a specific repository, can you provide the
  URL to that repository to help us with testing?

(New local repository being created in an empty directory)

If I omit --shared, there is no error
If there is only one file, there is no error
If the echo commands do not have characters, just adding a blank line, there is no error
If I turn off fscache, there is no error (git config --global core.fscache false)
All other filenames and contents also show the problem, for 2+ files
E.g. with files x,y,z,a,b, error happens on b - seems to be 2nd file in alphabetical order
The various GIT_TRACE_* options do not reveal anything useful, just normal setup up to trace: built-in: git add -A
Problem seems to have existed since at least 2017 (Google the 'unable to create temp...' error and git, e.g. https://stackoverflow.com/a/44040893 )
Confirmed in git version 2.26.2.windows.1
Problem does not occur in git version 2.9.3.windows.2 (2016) on Windows 10.0.18363.1316 with fscache

Bug originally reported to git@vger.kernel.org, was asked to post here as seems Windows specific.

[dscho]

Does it even make sense to use --shared on Windows? The permission model (ACLs) is so different from what Git expects (Unix' simplistic user/group/other read/write/executable model)...

[stevekmcc]

The same repository is cloned to multiple platforms. The command lines for repository creation and use are automated as part of integrating Git in a tool that works on multiple platforms. I'm not so worried about whether --shared can perfectly emulate the permissions familiar from Unix, more that simple core operations are broken in this case. This issue is about that bug; if anyone wants to suggest better permissions emulation, that could be raised as a separate issue.

[dscho]

The same repository is cloned to multiple platforms. The command lines for repository creation and use are automated as part of integrating Git in a tool that works on multiple platforms. I'm not so worried about whether --shared can perfectly emulate the permissions familiar from Unix, more that simple core operations are broken in this case. This issue is about that bug;

Have you given it a shot to debug this via gdb? see https://github.com/git-for-windows/git/wiki/Debugging-Git

A good idea would be to set a breakpoint on error_builtin().

if anyone wants to suggest better permissions emulation, that could be raised as a separate issue.

[stevekmcc]

Have you given it a shot to debug this via gdb? see https://github.com/git-for-windows/git/wiki/Debugging-Git

Sorry, I have no familiarity with the Git code, and precious little with gdb. All I was able to offer was to whittle it down to a minimal reproducible test case.

[dscho]

I'll leave this open, then, but have to caution you not to expect much. I, for one, am too short on time to play with this right now.

[dscho]

Closing as stale.