Re: [fuse-devel] [PATCH] FUSE/CUSE: implement direct mmap support

[Paul Schutte]

Sorry wrong thread !

Paul Schutte wrote:
> Hi.
>
> I am just sharing my thoughts on the matter.
>
> Maybe one can implement a separate "fuse sync" ioctl which can then be 
> called by a user space program say "fusersync" to sync all the fuse 
> filesystems you are allowed to.
>
> I implemented sync to my filesystem by means of an extended attribute.
> I now do "setfattr -nsync /mountpoint" to get the syncing done.
>
> This has the drawback that you can not easily put it in a script because 
> you need to know the mount point. I know one can write smart scripts to 
> figure out the mountpoint, but it would be nice if you can just say 
> "fusersync" and all the fuse filesystems that you are allowed to will 
> just sync.
>
> One can then maybe rename the system wide sync to say "sync.system" and 
> put a script in it's place which calls "fusersync;sync.system"
>
> Hopefully this idea might be useful.
>
> Regards
> Paul
>
> Goswin von Brederlow wrote:
>   
> > Tejun Heo <tj@xxxxxxxxxx> writes:
> >
> >   
> >     
> > > Implement FUSE direct mmap support.  The server can redirect client
> > > mmap requests to any SHMLBA aligned offset in the custom address space
> > > attached to the fuse channel.  The address space is managed by the
> > > server using mmap/munmap(2).  The SHMLBA alignment requirement is
> > > necessary to avoid cache aliasing issues on archs with virtually
> > > indexed caches as FUSE direct mmaps are basically shared memory
> > > between clients and the server.
> > >
> > > The direct mmap address space is backed by pinned kernel pages which
> > > are allocated on the first fault either from a client or the server.
> > > If used carelessly, this can easily waste and drain memory.
> > > Currently, a server must have CAP_SYS_ADMIN to manage dmmap regions by
> > > mmapping and munmapping the channel fd.
> > >     
> > >       
> > Does that mean that for example in unionfs-fuse when a user wants to
> > mmap a file I can just mmap the actual underlying file from the real
> > filesystem and any read/write access would then shortcut fuse and go
> > directly to the real file?
> >
> > MfG
> >         Goswin
> >
> > ------------------------------------------------------------------------------
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> >     
>
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