Re: [PATCH 6/7] iov: Helper macro to construct iovs covering existing variables or fields

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Apr 30, 2024 at 08:47:46PM +0200, Stefano Brivio wrote:
> On Mon, 29 Apr 2024 17:09:32 +1000
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > Laurent's recent changes mean we use IO vectors much more heavily in the
> > TCP code.  In many of those cases, and few others around the code base,
> > individual iovs of these vectors are constructed to exactly cover existing
> > variables or fields.  We can make initializing such iovs shorter and
> > clearer with a macro for the purpose.
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  iov.h |  3 +++
> >  tap.c |  3 +--
> >  tcp.c | 24 +++++++++---------------
> >  udp.c |  7 +++----
> >  4 files changed, 16 insertions(+), 21 deletions(-)
> > 
> > diff --git a/iov.h b/iov.h
> > index 6058af77..5668ca5f 100644
> > --- a/iov.h
> > +++ b/iov.h
> > @@ -18,6 +18,9 @@
> >  #include <unistd.h>
> >  #include <string.h>
> >  
> > +#define IOV_OF_LVALUE(lval) \
> > +	(struct iovec){ .iov_base = &(lval), .iov_len = sizeof(lval) }
> 
> I'm not sure if IOV_OF_LVALUE() is much clearer than IOV_FROM() or
> IOV_OF(). No strong preference though.

Yeah, I don't love the name but it was the best I came up with.  I
wanted to emphasise the fact that it must be given an lvalue - this
has to be a macro, not a function (even inline).

[snip]
> > @@ -315,8 +316,7 @@ static void udp_sock4_iov_init_one(const struct ctx *c, size_t i)
> >  		.iph = L2_BUF_IP4_INIT(IPPROTO_UDP)
> >  	};
> >  
> > -	siov->iov_base	= buf->data;
> > -	siov->iov_len	= sizeof(buf->data);
> > +	*siov		= IOV_OF_LVALUE(buf->data);
> >  
> >  	mh->msg_name	= &buf->s_in;
> >  	mh->msg_namelen	= sizeof(buf->s_in);
> > @@ -343,8 +343,7 @@ static void udp_sock6_iov_init_one(const struct ctx *c, size_t i)
> >  		.ip6h = L2_BUF_IP6_INIT(IPPROTO_UDP)
> >  	};
> >  
> > -	siov->iov_base	= buf->data;
> > -	siov->iov_len	= sizeof(buf->data);
> > +	*siov		 = IOV_OF_LVALUE(buf->data);
> 
> Extra whitespace between tabs and =.

Oops, fixed.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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