Re: [PATCH] [BSG]: Add support for structsg_io_v4->d[out,in]_iovec_count

From: FUJITA Tomonori
Date: Mon Jun 14 2010 - 02:23:29 EST

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.

This doesn't work on 32bit user/64bit kernel.

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.
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