netdev - RE: [PATCH v4 iproute2 2/7] rdma: Add dev object

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Date:   Tue, 15 Aug 2017 17:00:54 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Leon Romanovsky' <leonro@...lanox.com>
CC:     'Stephen Hemminger' <stephen@...workplumber.org>,
        Doug Ledford <dledford@...hat.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        Dennis Dalessandro <dennis.dalessandro@...el.com>,
        Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
        Jiri Pirko <jiri@...lanox.com>,
        "Ariel Almog" <ariela@...lanox.com>,
        Linux Netdev <netdev@...r.kernel.org>
Subject: RE: [PATCH v4 iproute2 2/7] rdma: Add dev object

From: Leon Romanovsky
> Sent: 15 August 2017 17:47
> On Tue, Aug 15, 2017 at 04:23:11PM +0000, David Laight wrote:
> > From: Stephen Hemminger
> > > Sent: 15 August 2017 17:12
> > > On Tue, 15 Aug 2017 16:00:15 +0300
> > > Leon Romanovsky <leonro@...lanox.com> wrote:
> > >
> > > > +
> > > > +static const char *dev_caps_to_str(uint32_t idx)
> > > > +{
> > > > +	uint64_t cap = 1 << idx;
> > > > +
> > > > +	switch (cap) {
> > > > +	case RDMA_DEV_RESIZE_MAX_WR: return "RESIZE_MAX_WR";
> > > > +	case RDMA_DEV_BAD_PKEY_CNTR: return "BAD_PKEY_CNTR";
> > ...
> > > > +	case RDMA_DEV_RAW_SCATTER_FCS: return "RAW_SCATTER_FCS";
> > > > +	case RDMA_DEV_RDMA_NETDEV_OPA_VNIC: return "RDMA_NETDEV_OPA_VNIC";
> > > > +	default: return "UNKNOWN";
> > > > +	}
> > >
> > > Could this be a table in future versions?
> >
> > Potentially you could define the constants using some pre-processor
> > 'magic' that would create the table for you.
> > Something like (but not compiled):
> >
> > #define RDMA_DEV_FLAGS(x) \
> > 	x(RESIZE_MAX_WR, 0) \
> > 	x(BAD_PKEY_CNTR, 1) \
> > (continue for all the bits)
> >
> > #define RDMA_DEV_ENUM(name, bit_no) RDMA_DEV_##name = BIT(bit_no),
> > enum {RDMA_DEV_FLAGS(RDMA_DEV_ENUM)};
> > #undef RDMA_DEV_ENUM
> >
> > #define RDMA_DEV_NAMES(name, bit_no) [bit_no] = #name,
> > static const char rdma_dev_names[] = {RDMA_DEV_FLAGS(RDMA_DEV_NAMES)};
I missed the #undef
> >
> 
> David,
> 
> How should I handle "uknown" fields without names?

The function that accesses rdma_dev_names[] checks ARRAY_SIZE()
and for a NULL pointer.

WRT the other comment, the spare pointers consume far less space than
the code for your switch statement.

	David