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

On Wed, Nov 07, 2012 at 01:45:27PM +0800, Wanlong Gao wrote: > 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. This is right.