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. Cheers, Jeremy -- 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
