On Thu, 2015-07-02 at 10:57 -0500, Jeremy White wrote: > On 07/02/2015 07:10 AM, Oliver Neukum wrote: > > On Thu, 2015-07-02 at 13:35 +0200, Hans de Goede wrote: > >> Hi, > >> > >> On 02-07-15 10:45, Oliver Neukum wrote: > >>> On Wed, 2015-07-01 at 10:06 +0100, Daniel P. Berrange wrote: > >>> > >>>> I don't really think it is sensible to be defining & implementing new > >>>> network services which can't support strong encryption and authentication. > >>>> Rather than passing the file descriptor to the kernel and having it do > >>>> the I/O directly, I think it would be better to dissassociate the kernel > >>>> from the network transport, and thus leave all sockets layer data I/O > >>>> to userspace daemons so they can layer in TLS or SASL or whatever else > >>>> is appropriate for the security need. > >>> > >>> Hi, > >>> > >>> this hits a fundamental limit. Block IO must be done entirely in kernel > >>> space or the system will deadlock. The USB stack is part of the block > >>> layer and the SCSI error handling. Thus if you involve user space you > >>> cannot honor memory allocation with GFP_NOFS and you break all APIs > >>> where we pass GFP_NOIO in the USB stack. > >>> > >>> Supposed you need to reset a storage device for error handling. > >>> Your user space programm does a syscall, which allocates memory > >>> and needs to launder pages. It proceeds to write to the storage device > >>> you wish to reset. > >>> > >>> It is the same problem FUSE has with writable mmap. You cannot do > >>> block devices in user space sanely. > >> > >> So how is this dealt with for usbip ? > > > > As far as I can tell, it isn't. Running a storage device over usbip > > is a bit dangerous. > > I don't follow that analysis. The usbip interactions with the usb stack > all seem to be atomic, and never trigger a syscall, as far as I can > tell. A port reset will flip a few bits and return. A urb enqueue > queues and wakes a different thread, and returns. The alternate thread > performs the sendmsg. > > I'm not suggesting that running a storage device over usbip is > especially safe, but I don't see the limit on the design. Are you referring to the current code or the proposed user space pipe? Regards Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
