Public bug reported:
Summary: The switch from vmhgfs to newer vmhgfs-fuse (in open-vm-tools)
results in data corruption and bus errors, due to particularly bad cache
coherency issues. I noticed this when using Git.
Detail:
I'm running Ubuntu 16.04 in a VM on my Macbook using VMware Fusion 8.0.
I use VMware Fusion's folder sharing to access the Mac's home directory from
Linux.
>From the Linux point of view, this is vmhgfs.
Previously I was running an older version of Ubuntu, and I upgraded it
recently.
Following the upgrade, I found the vmhgfs kernel module was no longer
available, vmhgfs-fuse was packaged as part of open-vm-tools, and the
syntax needed in /etc/fstab changed significantly. This was
inconvenient at the time, but not a serious problem.
What has emerged as a serious problem, though, is when I run almost any
Git command on one of these shared folders, I get one or both of these
errors:
- Reports of Git index corruption
- Git crashes with a Bus Error
Investigations found this test case:
$ echo foo > TEST; ls -l TEST; echo longer > TEST.new; mv TEST.new TEST;
ls -l TEST; sleep 6; ls -l TEST
-rw-rw-r-- 1 jamie jamie 4 May 7 03:26 TEST
-rw-rw-r-- 1 jamie jamie 4 May 7 03:26 TEST <-- This should have size
7, not 4.
-rw-rw-r-- 1 jamie jamie 7 May 7 03:26 TEST <-- After the 6 second
delay it shows the correct size.
That's awful behaviour for a filesystem, and it makes vmhgs-fuse quite
useless for serious interactions in which we write to the filesystem.
The Bus Errors which Git had were due to it calling mmap() with the
reported size, and then finding that some of the mapped range was not
readable because it wasn't the real size.
I tried disabling caching with the documented FUSE options:
- entry_timeout=0
- attr_timeout=0
Unfortunately vmhgfs-fuse ignores these. It has its own /hard-coded/ 5
second cache for attributes, separate from FUSE's cache, and it doesn't
even notice when it itself is responsible for changing a file on the
client size. The fact you can't disable the first and the second
doesn't work are individually both quite bad.
The source for vmhgfs-fuse defines the hard-coded timeout as
CACHE_TIMEOUT in cache.c.
Since the old vmhgfs worked, is there a way to install it on Ubuntu
16.04?
(This has forced me to stop using vmhgfs-fuse and look for alternatives
to access my Mac's home directory from the VM. Unfortunately NFS has
user id mapping problems (changing either user id isn't a solution for
me), Mac SMB can't convey executability to Linux CIFS (this also breaks
Git), and Samba smbclient currently has a bug whereby it can't connect
to Mac SMB shares with a password! So I am still looking for a
solution! :)
** Affects: open-vm-tools (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1579544
Title:
vmhgfs-fuse inconsistencies cause Git index corruption and Bus Error
crashes; older vmhgfs was fine
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