netdev - Re: [PATCH] SIW: User interface

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Date:	Tue, 5 Oct 2010 16:29:08 +0200
From:	Bernard Metzler <BMT@...ich.ibm.com>
To:	Steve Wise <swise@...ngridcomputing.com>
Cc:	linux-rdma@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] SIW: User interface

Steve Wise <swise@...ngridcomputing.com> wrote on 10/05/2010 04:17:34 PM:

> Steve Wise <swise@...ngridcomputing.com> 
> 10/05/2010 04:17 PM
> 
> To
> 
> Bernard Metzler <bmt@...ich.ibm.com>
> 
> cc
> 
> netdev@...r.kernel.org, linux-rdma@...r.kernel.org
> 
> Subject
> 
> Re: [PATCH] SIW: User interface
> 
> On 10/05/2010 01:54 AM, Bernard Metzler wrote:
> 
> 
> <snip>
> 
> > +
> > +/*
> > + * siw_post_send()
> > + *
> > + * Post a list of S-WR's to a SQ.
> > + *
> > + * @ofa_qp:   OFA QP contained in siw QP
> > + * @wr:      Null terminated list of user WR's
> > + * @bad_wr:   Points to failing WR in case of synchronous failure.
> > + */
> > +int siw_post_send(struct ib_qp *ofa_qp, struct ib_send_wr *wr,
> > +        struct ib_send_wr **bad_wr)
> > +{
> > +   struct siw_wqe   *wqe = NULL;
> > +   struct siw_qp   *qp = siw_qp_ofa2siw(ofa_qp);
> > +
> > +   unsigned long flags;
> > +   int rv = 0;
> > +
> > +   dprint(DBG_WR|DBG_TX, "(QP%d): state=%d\n",
> > +      QP_ID(qp), qp->attrs.state);
> > +
> > +   /*
> > +    * Acquire QP state lock for reading. The idea is that a
> > +    * user cannot move the QP out of RTS during TX/RX processing.
> > +    */
> > +   down_read(&qp->state_lock);
> > +
> > 
> 
> I don't think you can use a rw_semaphore here because it potentially can 

> block.  You cannot block/sleep in the post_send/post_recv (and some 
> other) RDMA provider functions.  See 
> Documentation/infiniband/core_locking.txt.
> 
> 
ah, ok.
with that, a down_read_trylock() would solve the issue...?
given the limited set of errno values - what would you suggest
as a meaningful return value? EBUSY, EINVAL, ...?

thanks!
bernard.

> Steve.

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