OSXFUSE - what exactly does the "local" mount option mean?

Question

I've implemented an OSXFUSE-based file system. It works fine on 10.8, but on Mavericks MS Word opens existing documents as blank (although I am, apparently, returning the correct data - I see the contents in the preview icon. Also, if I copy a file to a real hard drive and open it, it opens fine).

This issue is fixed on Mavericks if I mount my filesystem with the "local" flag. However, using this flag introduces other problems - e.g., it looks like it causes Finder to do some more aggressive caching, hence some file are not visible in Finder (although I can ls them in terminal).

Ideally I want to be able to mount the filesystem without this local flag (my implementation stores file on the network, so passing this flag looks wrong), but the problem with blank Word documents really puzzles me.

Answer 1

We have been able to track down the problem to - wait for it - Google Chrome. When Google Chrome is running while the volume is mounted, the problem appears. If Google Chrome is not running, Word/Excel/etc. files open just fine.

We've been in contact with Benjamin (OSXFUSE developer). Please also see his answer regarding this issue on the OSXFUSE mailing list:

https://groups.google.com/d/msg/osxfuse-group/URlw-n-Qakg/bLw2fHHDe7sJ

So far I have not found any bugs in osxfuse that might explain this behavior. The odd thing is that the files are not corrupted or empty. After copying the files to another volume they open just fine. Using LibreOffice to open the file on the FUSE volume works, too.

Chrome and Office seem to be based on the Carbon framework (which is deprecated since Mountain Lion). I believe the issue is somehow related to Carbon since non-Carbon apps do not seem to be affected. Every time a volume is mounted Chrome queries the volume’s capabilities and attributes (and maybe more). As far as I can tell all these file system operations return successful without any errors. But from this point on Office will fail to open documents.

In my opinion the two most likely reasons for this are:

1. osxfuse might break the VFS file system contract on Mavericks. I’ve been looking into this for some time now but I have not found any clues supporting this.
2. There might be a bug in the Carbon/CarbonCore framework. The odd thing is that there are no issues when using the stock network file systems afp or smb.

The two possible "fixes" (or rather "workarounds") for this issue seem to be (for now):

1. Use the "local" mount option (which might introduce other problems and is generally not recommend to use)
2. Do not use the "volname" mount option. The problem seems only to occur when the "volname" mount option is used. If no custom volume name is set, the problem seems not to occur and Excel/Word/etc. files open just fine - regardless whether Google Chrome was running at mount time.

Answer 2

I've seen the same and likewise local is not an option. Similar problems with Photoshop.

Some findings from my implementation

• The problem doesn't occur on first run after reboots.
• The problem begins occurring after program exit.
• I solved this problem by manually dismounting (and waiting a few seconds) before exiting my program. If unmount is successful, on next run the mount again performs fine.
• If the program ever terminates or dismounting fails (file in use, etc) then the volume's read-access is borked in Word/Photoshop on next mount.
• Rebooting resolves issue.

Does this match what you're seeing?