Re: [V9fs-developer] [PATCH 3/5] [net/9p] Add support for placing page addresses directly on the sg list.

["Venkateswararao Jujjuri (JV)" <jvrao@linux.vnet.ibm.com>]

Latchesar Ionkov wrote:
> Is there any particular reason p9_fcall to have pointers to pages
> instead of a scatterlist?

Given that page sizes are constant, all we need is offset into the first page.
IO size determines the last page. So we decided no need to put sg list in the
p9_fcall.

Thanks,
JV

> 
> Thanks,
>     Lucho
> 
> On Tue, Aug 17, 2010 at 11:27 AM, Venkateswararao Jujjuri (JV)
> <jvrao@linux.vnet.ibm.com> wrote:
>> This patch adds necessary infrastructure for placing page addresses
>> directly on the sg list for the server to consume.
>>
>> The newly added routine pack_sg_list_p() is just like pack_sg_list()
>> except that it takes page array as an input and directly places them on
>> the sg list after taking care of the first page offset.
>>
>> Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
>> Signed-off-by: Badari Pulavarty <pbadari@us.ibm.com>
>> ---
>>  include/net/9p/9p.h   |    6 ++++-
>>  net/9p/client.c       |    4 +++
>>  net/9p/trans_virtio.c |   59 ++++++++++++++++++++++++++++++++++++++++++++++--
>>  3 files changed, 65 insertions(+), 4 deletions(-)
>>
>> diff --git a/include/net/9p/9p.h b/include/net/9p/9p.h
>> index a8de812..382ef22 100644
>> --- a/include/net/9p/9p.h
>> +++ b/include/net/9p/9p.h
>> @@ -651,7 +651,11 @@ struct p9_fcall {
>>
>>        size_t offset;
>>        size_t capacity;
>> -
>> +       struct page **pdata;
>> +       uint32_t pdata_mapped_pages;
>> +       uint32_t pdata_off;
>> +       uint32_t pdata_write_len;
>> +       uint32_t pdata_read_len;
>>        uint8_t *sdata;
>>  };
>>
>> diff --git a/net/9p/client.c b/net/9p/client.c
>> index 29bbbbd..5487896 100644
>> --- a/net/9p/client.c
>> +++ b/net/9p/client.c
>> @@ -244,8 +244,12 @@ static struct p9_req_t *p9_tag_alloc(struct p9_client *c, u16 tag)
>>                }
>>                req->tc->sdata = (char *) req->tc + sizeof(struct p9_fcall);
>>                req->tc->capacity = c->msize;
>> +               req->tc->pdata_write_len = 0;
>> +               req->tc->pdata_read_len = 0;
>>                req->rc->sdata = (char *) req->rc + sizeof(struct p9_fcall);
>>                req->rc->capacity = c->msize;
>> +               req->rc->pdata_write_len = 0;
>> +               req->rc->pdata_read_len = 0;
>>        }
>>
>>        p9pdu_reset(req->tc);
>> diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
>> index 762c19f..8f86cb5 100644
>> --- a/net/9p/trans_virtio.c
>> +++ b/net/9p/trans_virtio.c
>> @@ -180,6 +180,44 @@ pack_sg_list(struct scatterlist *sg, int start, int limit, char *data,
>>        return index-start;
>>  }
>>
>> +/**
>> + * pack_sg_list_p - Pack a scatter gather list from an array of pages.
>> + * @sg: scatter/gather list to pack into
>> + * @start: which segment of the sg_list to start at
>> + * @limit: maximum segment to pack data to
>> + * @pdu: pdu prepared to put on the wire.
>> + * @count: amount of data to pack into the scatter/gather list
>> + *
>> + * This is just like pack_sg_list() except that it takes page array
>> + * as an input and directly places them on the sg list after taking
>> + * care of the first page offset.
>> + */
>> +
>> +static int
>> +pack_sg_list_p(struct scatterlist *sg, int start, int limit,
>> +               struct p9_fcall *pdu, int count)
>> +{
>> +       int s;
>> +       int i = 0;
>> +       int index = start;
>> +
>> +       if (pdu->pdata_off) {
>> +               s = min((int)(PAGE_SIZE - pdu->pdata_off), count);
>> +               sg_set_page(&sg[index++], pdu->pdata[i++], s, pdu->pdata_off);
>> +               count -= s;
>> +       }
>> +
>> +       while (count) {
>> +               BUG_ON(index > limit);
>> +               s = min((int)PAGE_SIZE, count);
>> +               sg_set_page(&sg[index++], pdu->pdata[i++], s, 0);
>> +               count -= s;
>> +       }
>> +
>> +       return index-start;
>> +}
>> +
>> +
>>  /* We don't currently allow canceling of virtio requests */
>>  static int p9_virtio_cancel(struct p9_client *client, struct p9_req_t *req)
>>  {
>> @@ -196,16 +234,31 @@ static int p9_virtio_cancel(struct p9_client *client, struct p9_req_t *req)
>>  static int
>>  p9_virtio_request(struct p9_client *client, struct p9_req_t *req)
>>  {
>> -       int in, out;
>> +       int in, out, outp, inp;
>>        struct virtio_chan *chan = client->trans;
>>        char *rdata = (char *)req->rc+sizeof(struct p9_fcall);
>>
>>        P9_DPRINTK(P9_DEBUG_TRANS, "9p debug: virtio request\n");
>>
>>        out = pack_sg_list(chan->sg, 0, VIRTQUEUE_NUM, req->tc->sdata,
>> -                                                               req->tc->size);
>> -       in = pack_sg_list(chan->sg, out, VIRTQUEUE_NUM-out, rdata,
>> +                       req->tc->size);
>> +
>> +       BUG_ON(req->tc->pdata_write_len && req->tc->pdata_read_len);
>> +
>> +       if (req->tc->pdata_write_len) {
>> +               outp = pack_sg_list_p(chan->sg, out, VIRTQUEUE_NUM,
>> +                                       req->tc, req->tc->pdata_write_len);
>> +               out += outp;
>> +       }
>> +       if (req->tc->pdata_read_len) {
>> +               inp = pack_sg_list(chan->sg, out, VIRTQUEUE_NUM, rdata, 11);
>> +               in = pack_sg_list_p(chan->sg, out+inp, VIRTQUEUE_NUM,
>> +                                       req->tc, req->tc->pdata_read_len);
>> +               in += inp;
>> +       } else {
>> +               in = pack_sg_list(chan->sg, out, VIRTQUEUE_NUM, rdata,
>>                                                                client->msize);
>> +       }
>>
>>        req->status = REQ_STATUS_SENT;
>>
>> --
>> 1.6.5.2
>>
>>
>> ------------------------------------------------------------------------------
>> This SF.net email is sponsored by
>>
>> Make an app they can't live without
>> Enter the BlackBerry Developer Challenge
>> http://p.sf.net/sfu/RIM-dev2dev
>> _______________________________________________
>> V9fs-developer mailing list
>> V9fs-developer@lists.sourceforge.net
>> https://lists.sourceforge.net/lists/listinfo/v9fs-developer
>>