Append to file broken

[hsandmeyer]

I can not append to files any more. In the mounted directory:

$ echo foo > test.txt
$ echo bar >> test.txt
$ cat test.txt
bar

Same happens using other programs than the shell

System is arch-linux with newest updates.

sshfs --version

SSHFS version 3.0.0
FUSE library version 3.1.0
using FUSE kernel interface version 7.26
fusermount3 version: 3.1.0

[myagues]

Try disabling writeback_cache with -o writeback_cache=no.

[hsandmeyer]

Thank you. That helps

[Nikratio]

Thanks for the report! I will look into it ASAP.

[Nikratio]

A very similar problem with append operations is actually present in the passthrough_fh example that comes with libfuse itself. If writeback cache is enabled, we get:

$ echo foo > test.txt
$ echo bar >> test.txt
bash: echo: write error: Bad file descriptor
$ cat test.txt 
foo

[Nikratio]

Alright, so the problem is that SSHFS opens the file write-only, but writeback cache requires the ability to read the file. Opening read-write fixes the problem.

But the important question is: why aren't we getting an error from the remote server when trying to read from a write-only file? This is what's responsible for getting silent data corruptions instead of an error on the second write.

[Nikratio]

Reported the issue to the openssh folks. Should soon show up on https://marc.info/?l=openssh-unix-dev&r=1&b=201708&w=2.