lkml.org 
[lkml]   [2017]   [Apr]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH v2 15/21] xen-blkfront: Make use of the new sg_map helper function
    On Thu, Apr 27, 2017 at 02:19:24PM -0600, Logan Gunthorpe wrote:
    >
    >
    > On 26/04/17 01:37 AM, Roger Pau Monné wrote:
    > > On Tue, Apr 25, 2017 at 12:21:02PM -0600, Logan Gunthorpe wrote:
    > >> Straightforward conversion to the new helper, except due to the lack
    > >> of error path, we have to use SG_MAP_MUST_NOT_FAIL which may BUG_ON in
    > >> certain cases in the future.
    > >>
    > >> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
    > >> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
    > >> Cc: Juergen Gross <jgross@suse.com>
    > >> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    > >> Cc: "Roger Pau Monné" <roger.pau@citrix.com>
    > >> drivers/block/xen-blkfront.c | 20 +++++++++++---------
    > >> 1 file changed, 11 insertions(+), 9 deletions(-)
    > >>
    > >> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
    > >> index 3945963..ed62175 100644
    > >> +++ b/drivers/block/xen-blkfront.c
    > >> @@ -816,8 +816,9 @@ static int blkif_queue_rw_req(struct request *req, struct blkfront_ring_info *ri
    > >> BUG_ON(sg->offset + sg->length > PAGE_SIZE);
    > >>
    > >> if (setup.need_copy) {
    > >> - setup.bvec_off = sg->offset;
    > >> - setup.bvec_data = kmap_atomic(sg_page(sg));
    > >> + setup.bvec_off = 0;
    > >> + setup.bvec_data = sg_map(sg, 0, SG_KMAP_ATOMIC |
    > >> + SG_MAP_MUST_NOT_FAIL);
    > >
    > > I assume that sg_map already adds sg->offset to the address?
    >
    > Correct.
    >
    > > Also wondering whether we can get rid of bvec_off and just increment bvec_data,
    > > adding Julien who IIRC added this code.
    >
    > bvec_off is used to keep track of the offset within the current mapping
    > so it's not a great idea given that you'd want to kunmap_atomic the
    > original address and not something with an offset. It would be nice if
    > this could be converted to use the sg_miter interface but that's a much
    > more invasive change that would require someone who knows this code and
    > can properly test it. I'd be very grateful if someone actually took that on.

    blkfront is one of the drivers I looked at, and it appears to only be
    memcpying with the bvec_data pointer, so I wonder why it does not use
    sg_copy_X_buffer instead..

    Jason

    \
     
     \ /
      Last update: 2017-04-27 22:55    [W:2.858 / U:0.968 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site