RE: [PATCH V3 1/5] RDMA/core: Transport-independent access flags

["Steve Wise" <swise@opengridcomputing.com>]

> -----Original Message-----
> From: Christoph Hellwig [mailto:hch@infradead.org]
> Sent: Monday, July 06, 2015 12:25 AM
> To: Steve Wise
> Cc: dledford@redhat.com; sagig@mellanox.com; ogerlitz@mellanox.com; roid@mellanox.com; linux-rdma@vger.kernel.org;
> eli@mellanox.com; target-devel@vger.kernel.org; linux-nfs@vger.kernel.org; trond.myklebust@primarydata.com; bfields@fieldses.org
> Subject: Re: [PATCH V3 1/5] RDMA/core: Transport-independent access flags
> 
> On Sun, Jul 05, 2015 at 06:22:00PM -0500, Steve Wise wrote:
> > The semantics for MR access flags are not consistent across RDMA
> > protocols.  So rather than have applications try and glean what they
> > need, have them pass in the intended roles and attributes for the MR to
> > be allocated and let the RDMA core select the appropriate access flags
> > given the roles, attributes, and device capabilities.
> >
> > We introduce rdma_mr_roles and rdma_mr_attributes that enumerate the
> > possible roles and attributes for a MR.  These are documented in the
> > enums themselves.
> >
> > New services exported:
> >
> > rdma_device_access_flags() - given the intended MR roles and attributes
> > passed in, return the ib_access_flags bits for the device.
> >
> > rdma_get_dma_mr() - allocate a dma mr using the applications intended
> > MR roles and MR attributes.  This uses rdma_device_access_flags().
> >
> > rdma_fast_reg_access_flags() - return the ib_access_flags bits needed
> > for a fast register WR given the applications intended MR roles and
> > MR attributes.  This uses rdma_device_access_flags().
> >
> > Signed-off-by: Steve Wise <swise@opengridcomputing.com>
> > ---
> >
> >  drivers/infiniband/core/verbs.c |   30 +++++++++++
> >  include/rdma/ib_verbs.h         |  106 +++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 136 insertions(+), 0 deletions(-)
> >
> > diff --git a/drivers/infiniband/core/verbs.c b/drivers/infiniband/core/verbs.c
> > index bac3fb4..f42595c 100644
> > --- a/drivers/infiniband/core/verbs.c
> > +++ b/drivers/infiniband/core/verbs.c
> > @@ -1144,6 +1144,36 @@ struct ib_mr *ib_get_dma_mr(struct ib_pd *pd, int mr_access_flags)
> >  }
> >  EXPORT_SYMBOL(ib_get_dma_mr);
> >
> > +int rdma_device_access_flags(struct ib_pd *pd, int roles, int attrs)
> > +{
> > +	int access_flags = attrs;
> 
> Please add an assert for the values that are allowed for attrs.
> 
> It also would be highly useful to add a kerneldoc comment describing
> the function and the parameters.  Also __bitwise sparse tricks
> to ensure the right flags are passed wouldn't be a too bad idea.
> 

Can you explain the "__bitwise sparse tricks"?  Or point me to an example.  

> > +/**
> > + * rdma_mr_attributes - attributes for rdma memory regions
> > + */
> > +enum {
> > +	RDMA_MRA_ZERO_BASED		= IB_ZERO_BASED,
> > +	RDMA_MRA_ACCESS_ON_DEMAND	= IB_ACCESS_ON_DEMAND,
> > +};
> 
> Why not specfiy these as separate nuerical namespace?
> 

To avoid having to translate them. 

> > +/**
> > + * rdma_device_access_flags - Returns the device-specific MR access flags.
> > + * @pd: The protection domain associated with the memory region.
> > + * @roles: The intended roles of the MR
> > + * @attrs: The desired attributes of the MR
> > + *
> > + * Use the intended roles from @roles along with @attrs and the device
> > + * capabilities to generate the needed access rights.
> > + *
> > + * Return: the ib_access_flags value needed to allocate the MR.
> > + */
> > +int rdma_device_access_flags(struct ib_pd *pd, int roles, int attrs);
> 
> Oh, here we have kerneldoc comments, just in the wrong place.  Please
> move them to the function defintion.

Ok.