Re: [PATCH 1/4] treewide: Use 'z' length modifier for size_t/ssize_t conversions

[Stefano Brivio <sbrivio@redhat.com>]

On Thu, 30 Nov 2023 11:15:47 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Wed, Nov 29, 2023 at 02:46:07PM +0100, Stefano Brivio wrote:
> > Types size_t and ssize_t are not necessarily long, it depends on the
> > architecture.  
> 
> Most LGTM, but a couple of nits:
> 
> [snip]
> > @@ -106,7 +106,7 @@ void *packet_get_do(const struct pool *p, size_t idx, size_t offset,
> >  
> >  	if (p->pkt[idx].offset + len + offset > p->buf_size) {
> >  		if (func) {
> > -			trace("packet offset plus length %lu from size %lu, "
> > +			trace("packet offset plus length %lu from size %zu, "  
> 
> The change here is certainly correct.  But the remaining %lu is
> dubious.  The value given is the sum of a uint32_t and two size_t, so
> it could depend on platform what exactly that will be promoted to.  I
> think we should probably either cast the result explicitly to (size_t)
> and use %zu, or cast to (uint32_t) and use "%" PRIu32.
> 
> [snip]
> > diff --git a/tcp_splice.c b/tcp_splice.c
> > index a5c1332..8d08bb4 100644
> > --- a/tcp_splice.c
> > +++ b/tcp_splice.c
> > @@ -321,7 +321,7 @@ static int tcp_splice_connect_finish(const struct ctx *c,
> >  
> >  			if (fcntl(conn->pipe[side][0], F_SETPIPE_SZ,
> >  				  c->tcp.pipe_size)) {
> > -				trace("TCP (spliced): cannot set %d->%d pipe size to %lu",
> > +				trace("TCP (spliced): cannot set %d->%d pipe size to %zu",
> >  				      side, !side, c->tcp.pipe_size);
> >  			}
> >  		}
> > @@ -554,7 +554,7 @@ retry:
> >  		readlen = splice(conn->s[fromside], NULL,
> >  				 conn->pipe[fromside][1], NULL, c->tcp.pipe_size,
> >  				 SPLICE_F_MOVE | SPLICE_F_NONBLOCK);
> > -		trace("TCP (spliced): %li from read-side call", readlen);
> > +		trace("TCP (spliced): %zi from read-side call", readlen);
> >  		if (readlen < 0) {
> >  			if (errno == EINTR)
> >  				goto retry;
> > @@ -580,7 +580,7 @@ eintr:
> >  		written = splice(conn->pipe[fromside][0], NULL,
> >  				 conn->s[!fromside], NULL, to_write,
> >  				 SPLICE_F_MOVE | more | SPLICE_F_NONBLOCK);
> > -		trace("TCP (spliced): %li from write-side call (passed %lu)",
> > +		trace("TCP (spliced): %zi from write-side call (passed %zu)",
> >  		      written, to_write);  
> 
> 'to_write' is actually an ssize_t which would suggest %zi.  However
> looking at the code, I think to_write probably *should* be a size_t
> instead.

Oops, I didn't notice. Well, I know we're passing it to splice(), but
we're also using it like this:

		if (!never_read && written < to_write) {
			to_write -= written;
			goto retry;
		}

so I'd rather keep it as ssize_t for the moment (and re-spin this
series with a %zi here), just in case we happen to do something silly
with it and ssize_t is saving us.

-- 
Stefano