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

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

[Stefano Brivio]

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>
---
 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);
 		}
-- 
@@ -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);
 		}
-- 
2.43.0

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

[David Gibson]

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

[Stefano Brivio]

On Fri, 25 Oct 2024 11:21:59 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> 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.

Right, that might happen, but I also thought that that would be
interesting enough for us to print, especially because we first probe
for a size that we can set at least for one pool of pipes.

If we get a bigger size than what we wanted to set, it's somewhat more
likely that we'd have issues setting the same size for other pipes.

-- 
Stefano