On Mon, 2010-06-14 at 15:22 +0900, FUJITA Tomonori wrote: > On Sun, 13 Jun 2010 23:11:29 -0700 > "Nicholas A. Bellinger" <nab@xxxxxxxxxxxxxxx> wrote: > > > From: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx> > > > > Greetings Jens and co, > > > > This patch adds the missing support to block/bsg.c:bsg_map_hdr() to accept > > struct sg_io_v4->d[out,in]_iovec_count and process struct sg_io_v4->d[out,in]_xferp memory > > containing userspace iovecs for kernel level BSG. It adds a new wrapper bsg_rq_map_user_iov() > > that will call copy_from_user() and blk_rq_map_user_iov() following the original SG_IO logic in > > drivers/scsi/sg.c:sg_start_req(). > > > > So far this has been tested on a x86_64 v2.6.34 KVM Host with TCM_Loop Virtual SAS Port/LUNs > > into a x86_64 v2.6.26 KVM Guest with Megasas 8707EM2 HBA Emulation + my new scsi-bsg backstore code. > > > > Please consider this for v2.6.36 as it will be required in order for QEMU-KVM MegaSAS and VirtIO HBA > > emulation using QEMU scatterlist memory and BSG backstores. > > > > Signed-off-by: Nicholas A. Bellinger <nab@xxxxxxxxxxxxxxx> > > --- > > block/bsg.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++-------- > > 1 files changed, 47 insertions(+), 8 deletions(-) > > This have been rejected several times. > I guess that would explain why the iovec_count structure members are part of struct sg_io_v4 and block/bsg.c:bsg_map_hdr() silently accepts and overwrites them.. :( > This doesn't work on 32bit user/64bit kernel. Hmmm, being able to use QEMU-KVM HBA emulation with userspace scatterlist memory for the various HBA emulation with a matched user/kernel is still useful though, yes..? Being able to handle TMR emulation from QEMU-KVM HBA emulation would also be useful I think. Having QEMU-KVM fall back to SG_IO for the 32bit/64bit kernel would be accpetable for me if we can still make BSG + iovecs work for the typical case. > > The compat code doesn't work for the read/write interface (does for > the ioctl interface though). So we can't support this feature cleanly. So I am curious to see if there will be a performance improvement between QEMU-KVM + scsi-bsg w/ AIO IOVECs compared to the legacy SG_IO ioctl(). Anyways, I will post my QEMU-KVM scsi-bsg patches and run some benchmarks this week with this patch on 5500 series Nehalem so see aside from the userspace TMR case how useful having a BSG backstore for QEMU-KVM may be. Best, --nab -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
