Re: [PATCH v4 3/3] libceph: just wait for more data to be available on the socket

[Jeff Layton <jlayton@kernel.org>]

On Mon, 2024-01-22 at 17:55 +0100, Ilya Dryomov wrote:
> On Mon, Jan 22, 2024 at 4:02 PM Jeff Layton <jlayton@kernel.org> wrote:
> > 
> > On Thu, 2024-01-18 at 18:50 +0800, xiubli@redhat.com wrote:
> > > From: Xiubo Li <xiubli@redhat.com>
> > > 
> > > The messages from ceph maybe split into multiple socket packages
> > > and we just need to wait for all the data to be availiable on the
> > > sokcet.
> > > 
> > > This will add 'sr_total_resid' to record the total length for all
> > > data items for sparse-read message and 'sr_resid_elen' to record
> > > the current extent total length.
> > > 
> > > URL: https://tracker.ceph.com/issues/63586
> > > Signed-off-by: Xiubo Li <xiubli@redhat.com>
> > > ---
> > >  include/linux/ceph/messenger.h |  1 +
> > >  net/ceph/messenger_v1.c        | 32 +++++++++++++++++++++-----------
> > >  2 files changed, 22 insertions(+), 11 deletions(-)
> > > 
> > > diff --git a/include/linux/ceph/messenger.h b/include/linux/ceph/messenger.h
> > > index 2eaaabbe98cb..ca6f82abed62 100644
> > > --- a/include/linux/ceph/messenger.h
> > > +++ b/include/linux/ceph/messenger.h
> > > @@ -231,6 +231,7 @@ struct ceph_msg_data {
> > > 
> > >  struct ceph_msg_data_cursor {
> > >       size_t                  total_resid;    /* across all data items */
> > > +     size_t                  sr_total_resid; /* across all data items for sparse-read */
> > > 
> > >       struct ceph_msg_data    *data;          /* current data item */
> > >       size_t                  resid;          /* bytes not yet consumed */
> > > diff --git a/net/ceph/messenger_v1.c b/net/ceph/messenger_v1.c
> > > index 4cb60bacf5f5..2733da891688 100644
> > > --- a/net/ceph/messenger_v1.c
> > > +++ b/net/ceph/messenger_v1.c
> > > @@ -160,7 +160,9 @@ static size_t sizeof_footer(struct ceph_connection *con)
> > >  static void prepare_message_data(struct ceph_msg *msg, u32 data_len)
> > >  {
> > >       /* Initialize data cursor if it's not a sparse read */
> > > -     if (!msg->sparse_read)
> > > +     if (msg->sparse_read)
> > > +             msg->cursor.sr_total_resid = data_len;
> > > +     else
> > >               ceph_msg_data_cursor_init(&msg->cursor, msg, data_len);
> > >  }
> > > 
> > > 
> > 
> > Sorry, disregard my last email.
> > 
> > I went and looked at the patch in the tree, and I better understand what
> > you're trying to do. We already have a value that gets set to data_len
> > called total_resid, but that is a nonsense value in a sparse read,
> > because we can advance farther through the receive buffer than the
> > amount of data in the socket.
> 
> Hi Jeff,
> 
> I see that total_resid is set to sparse_data_requested(), which is
> effectively the size of the receive buffer, not data_len.  (This is
> ignoring the seemingly unnecessary complication of trying to support
> normal reads mixed with sparse reads in the same message, which I'm
> pretty sure doesn't work anyway.)
> 

Oh right. I missed that bit when I was re-reviewing this. Once we're in
a sparse read we'll override that value. Ok, so maybe we don't need
sr_total_resid.

> With that, total_resid should represent the amount that needs to be
> filled in (advanced through) in the receive buffer.  When total_resid
> reaches 0, wouldn't that mean that the amount of data in the socket is
> also 0?  If not, where would the remaining data in the socket go?
> 

With a properly formed reply, then I think yes, there should be no
remaining data in the socket at the end of the receive.

At this point I think I must just be confused about the actual problem.
I think I need a detailed description of it before I can properly review
this patch.

-- 
Jeff Layton <jlayton@kernel.org>