Re: [fuse-devel] making fuse mount hang

[Mohit A. <ext...@gm...>]

>
> You should rather make the filesystem fault tolerant by not crashing ;)
>
> Seriously, what you require is impossible: one mount cannot magically
> replace another with all open files, etc migrated to the new one.
>


Well, no matter how well one writes code, crashes do happen sometimes - and
I'd like the application to be shielded from it. With rapid development of a
complex filesystem, it becomes even harder.

I could definitely get the desired effect with say an NFS server which runs
on the same machine - if the server crashes, the mount point is hung, and
the NFS server can be restarted safely.

In fact, I was wondering about the advantages/disadvantages of using fuse vs
a loopback NFS server. Any thoughts on that ? The one disadvantage that's
keeping me from going that route is that the freely available sunrpc library
is not multi-threaded and it takes some work to make it so. Without that,
essentially the NFS server can only have one request outstanding at any
time. One of the past companies I worked for built a user-level distributed
NFS server and it had to solve that issue.


>
> If such high level of fault tolerance is really an issue (I suspect
> not, it's much easier to just fix the bugs), then you can write a
> simple persistent layer that forwards requests to another, restartable
> layer which has all the complexity.
>

That would involve yet another context switch and more data copying - in the
short term, I'll just work with making both the application as well as the
fuse process crash together and restart both of them if necessary.


- Mohit