[fuse-devel] vanished files after rename

[Dietmar M. <di...@pr...>]

Hi all,

we recently observed very strange behavior with 'rename'. Our software
uses temporary files to make sure file creation is atomic. For example,
we first create 'testfile.tmp.XYZ', write the file, and then simply
rename the file to 'testfile'. The strange thing is that 'testfile'
vanish from time to time when read from other processes.

I assembled a test case using 'fusexmp.c'. Simply download attached 
fuse-rename-bug.tgz package and do:

# tar xf fuse-rename-bug.tgz
# cd fuse-rename-bug
# Note: needs to be run as root (sorry)
# make
Start test
Waiting for CRM [10224] and LRM [10222]
write:0:Wed Oct 14 09:36:33 2015
read:0:Wed Oct 14 09:36:33 2015
read:1:Wed Oct 14 09:36:33 2015
write:1:Wed Oct 14 09:36:33 2015
READ ERROR: can't open './testmnt/test-file' - No such file or directory
read:2:Wed Oct 14 09:36:33 2015
write:2:Wed Oct 14 09:36:33 2015
read:3:Wed Oct 14 09:36:33 2015
read:4:Wed Oct 14 09:36:33 2015
write:3:Wed Oct 14 09:36:33 2015
READ ERROR: can't open './testmnt/test-file' - No such file or directory
exit[10222]: 0
write:4:Wed Oct 14 09:36:33 2015
exit[10224]: 0
End test

The real test is inside test_fuse_exmp.pl, which mounts fusexmp at 
directory './testmnt'. So when you are done with testing you should

# umount ./testmnt

AFAIK this bug triggers with any fuse based file system, for example sshfs.
I guess it is quite dangerous for any software that assume a rename
is an atomic action.

Any idea how to fix that?