Re: [libvirt] [PATCH v7 2/6] add fuse support for libvirt lxc

On 11/07/2012 11:54 AM, Gao feng wrote: > 于 2012年11月06日 20:55, Richard W.M. Jones 写道: >> On Tue, Nov 06, 2012 at 07:50:33PM +0800, Gao feng wrote: >>> 于 2012年11月06日 17:11, Richard W.M. Jones 写道: >>>> On Tue, Nov 06, 2012 at 04:54:59PM +0800, Gao feng wrote: >>>>> Because libvirt_lxc create a thread to mount fuse filesystem. >>>>> and then libvirt_lxc will try to access the fuse filesystem. >>>>> >>>>> Without waiting,libvirt_lxc may access fuse before it is mounted. >>>>> >>>>> And I can't find a better way to make accessing fuse after the fuse >>>>> being mounted,because fuse_main will return until fuse being unmounted,so >>>>> I don't know how to pass message to tell libvirt_lxc whether the fuse is >>>>> mounted success. >>>> >>>> Oh I see. This is solvable, but I believe that you cannot use >>>> fuse_main. You have to look at the fuse sources (quite complex!) and >>>> do the individual fuse operations. >>>> >>>> Have a look at how libguestfs does it ... >>>> >>>> https://github.com/libguestfs/libguestfs/blob/master/src/fuse.c#L911 >>>> http://libguestfs.org/guestfs.3.html#mount-local >>>> >>> >>> >>> Thanks for the information. >>> >>> Can fuse_mount & fuse_new & fuse_loop avoid the waiting? >>> >>> It seems has the same problem. >> >> It waits, but it doesn't busy wait in a loop. The first access to the >> filesystem hangs until the thread which is handling the filesystem is >> listening for requests. >> > > It makes me confuse. > > There are two threads(A and B). > thread A mounts fuse filesystem on mountpoint /mnt/fuse. > thread B try to access file /mnt/fuse/meminfo. and we don't > know which thread will execute first. > > The information I got from your comment is that because thread A > doesn't mount fuse to /mnt/fuse, when thread B access to the > /mnt/fuse/meminfo,it will hang. I am right? If I'm not wrong, I think Rich means that you should create the mountpoint and the operations using fuse_mount and fuse_new before you create the thread B, then make another thread A using fuse_loop to loop behind. Then if thread B try to access the mountpoint before thread A runs, B will hang until thread A runs into the loop.