[PATCH] tap: Explicitly cast TUNSETIFF to fix build warning with musl on ppc64le

[PATCH] tap: Explicitly cast TUNSETIFF to fix build warning with musl on ppc64le

[Stefano Brivio]

On ppc64le, TUNSETIFF happens to be 2147767498, which is bigger than
INT_MAX (2^31 - 1), and musl declares the second argument of ioctl()
as 'int', not 'unsigned long' like glibc does, probably because of how
POSIX specifies the equivalent argument, int dcmd, in posix_devctl(),
so gcc reports a warning:

tap.c: In function 'tap_ns_tun':
tap.c:1291:24: warning: overflow in conversion from 'long unsigned int' to 'int' changes value from '2147767498' to '-2147199798' [-Woverflow]
 1291 |         rc = ioctl(fd, TUNSETIFF, &ifr);
      |                        ^~~~~~~~~

We don't care about that overflow, so explicitly cast TUNSETIFF to
int.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 tap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tap.c b/tap.c
index cfb82e9..f638f2c 100644
--- a/tap.c
+++ b/tap.c
@@ -1288,7 +1288,7 @@ static int tap_ns_tun(void *arg)
 	if (fd < 0)
 		die_perror("Failed to open() /dev/net/tun");
 
-	rc = ioctl(fd, TUNSETIFF, &ifr);
+	rc = ioctl(fd, (int)TUNSETIFF, &ifr);
 	if (rc < 0)
 		die_perror("TUNSETIFF ioctl on /dev/net/tun failed");
 
-- 
@@ -1288,7 +1288,7 @@ static int tap_ns_tun(void *arg)
 	if (fd < 0)
 		die_perror("Failed to open() /dev/net/tun");
 
-	rc = ioctl(fd, TUNSETIFF, &ifr);
+	rc = ioctl(fd, (int)TUNSETIFF, &ifr);
 	if (rc < 0)
 		die_perror("TUNSETIFF ioctl on /dev/net/tun failed");
 
-- 
2.43.0

Re: [PATCH] tap: Explicitly cast TUNSETIFF to fix build warning with musl on ppc64le

[David Gibson]

[-- Attachment #1: Type: text/plain, Size: 1586 bytes --]

On Wed, Oct 30, 2024 at 09:50:30PM +0100, Stefano Brivio wrote:
> On ppc64le, TUNSETIFF happens to be 2147767498, which is bigger than
> INT_MAX (2^31 - 1), and musl declares the second argument of ioctl()
> as 'int', not 'unsigned long' like glibc does, probably because of how
> POSIX specifies the equivalent argument, int dcmd, in posix_devctl(),
> so gcc reports a warning:
> 
> tap.c: In function 'tap_ns_tun':
> tap.c:1291:24: warning: overflow in conversion from 'long unsigned int' to 'int' changes value from '2147767498' to '-2147199798' [-Woverflow]
>  1291 |         rc = ioctl(fd, TUNSETIFF, &ifr);
>       |                        ^~~~~~~~~
> 
> We don't care about that overflow, so explicitly cast TUNSETIFF to
> int.
> 
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Ugly, but I don't see a better way to deal with it.

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

> ---
>  tap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tap.c b/tap.c
> index cfb82e9..f638f2c 100644
> --- a/tap.c
> +++ b/tap.c
> @@ -1288,7 +1288,7 @@ static int tap_ns_tun(void *arg)
>  	if (fd < 0)
>  		die_perror("Failed to open() /dev/net/tun");
>  
> -	rc = ioctl(fd, TUNSETIFF, &ifr);
> +	rc = ioctl(fd, (int)TUNSETIFF, &ifr);
>  	if (rc < 0)
>  		die_perror("TUNSETIFF ioctl on /dev/net/tun failed");
>  

-- 
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

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]