Re: [PATCH] tcp_splice: fcntl(2) returns the size of the pipe, if F_SETPIPE_SZ succeeds

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

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On Fri, Oct 25, 2024 at 01:04:18AM +0200, Stefano Brivio wrote:
> Don't report bogus failures (with --trace) just because the return
> value is not zero.
> 
> Link: https://github.com/containers/podman/issues/24219
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

I think this is technicall still not quite right, because F_SETPIPE_SZ
can return a value larger than the one requested.  AFAICT we don't get
that just becauase the way we allocate pipe sizes and the way the
kernel does are in alignment.

But it suppresses a bogus error and doesn't do any harm so:

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  tcp_splice.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tcp_splice.c b/tcp_splice.c
> index f112cfe..93f8bce 100644
> --- a/tcp_splice.c
> +++ b/tcp_splice.c
> @@ -320,7 +320,7 @@ static int tcp_splice_connect_finish(const struct ctx *c,
>  			}
>  
>  			if (fcntl(conn->pipe[sidei][0], F_SETPIPE_SZ,
> -				  c->tcp.pipe_size)) {
> +				  c->tcp.pipe_size) != (int)c->tcp.pipe_size) {
>  				flow_trace(conn,
>  					   "cannot set %d->%d pipe size to %zu",
>  					   sidei, !sidei, c->tcp.pipe_size);
> @@ -672,7 +672,7 @@ static void tcp_splice_pipe_refill(const struct ctx *c)
>  			continue;
>  
>  		if (fcntl(splice_pipe_pool[i][0], F_SETPIPE_SZ,
> -			  c->tcp.pipe_size)) {
> +			  c->tcp.pipe_size) != (int)c->tcp.pipe_size) {
>  			trace("TCP (spliced): cannot set pool pipe size to %zu",
>  			      c->tcp.pipe_size);
>  		}

-- 
David Gibson (he or they)	| 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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