On Wed, May 06, 2015 at 09:09:36AM +0200, Bart Van Assche wrote: > On 05/05/15 23:06, Christoph Hellwig wrote: > >The contiguous requirements isn't something we can alway guarantee. > >While a lot of I/O will have that form the form where there are holes > >can happen, although it's not common. > > Indeed. That is why there is code in the SRP initiator that uses multiple > FRWR registrations when a discontiguous SG-list is passed to that driver by > the SCSI mid-layer. Some time ago I had posted a test program that makes the > SCSI mid-layer submit a discontiguous I/O request to a SCSI LLD (see also > https://www.mail-archive.com/linux-rdma@xxxxxxxxxxxxxxx/msg21224.html). Note that block layer now has the (fairly misnamed) QUEUE_FLAG_SG_GAPS flag, which ensures drivers don't see S/G lists like this one. I haven't ever seen normal TYPE_FS producers submit bios like that, so in practice the effect is to reject vectored SG_IO uses like your test program. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
