[iproute2, RESEND PATCH 1/2] arpd: use designated initializers for msghdr structure

[iproute2, RESEND PATCH 1/2] arpd: use designated initializers for msghdr structure

[Dario Binacchi]

This patch fixes the following error:

arpd.c:442:17: error: initialization of 'int' from 'void *' makes integer from pointer without a cast [-Wint-conversion]
  442 |                 NULL,   0,

raised by Buildroot autobuilder [1].

In the case in question, the analysis of socket.h [2] containing the
msghdr structure shows that it has been modified with the addition of
padding fields, which cause the compilation error. The use of designated
initializers allows the issue to be fixed.

struct msghdr {
	void *msg_name;
	socklen_t msg_namelen;
	struct iovec *msg_iov;
#if __LONG_MAX > 0x7fffffff && __BYTE_ORDER == __BIG_ENDIAN
	int __pad1;
#endif
	int msg_iovlen;
#if __LONG_MAX > 0x7fffffff && __BYTE_ORDER == __LITTLE_ENDIAN
	int __pad1;
#endif
	void *msg_control;
#if __LONG_MAX > 0x7fffffff && __BYTE_ORDER == __BIG_ENDIAN
	int __pad2;
#endif
	socklen_t msg_controllen;
#if __LONG_MAX > 0x7fffffff && __BYTE_ORDER == __LITTLE_ENDIAN
	int __pad2;
#endif
	int msg_flags;
};

[1] http://autobuild.buildroot.org/results/e4cdfa38ae9578992f1c0ff5c4edae3cc0836e3c/
[2] iproute2/host/mips64-buildroot-linux-musl/sysroot/usr/include/sys/socket.h

Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
---
 misc/arpd.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/misc/arpd.c b/misc/arpd.c
index e77ef53928a2..b4935c23eebb 100644
--- a/misc/arpd.c
+++ b/misc/arpd.c
@@ -437,10 +437,10 @@ static void get_kern_msg(void)
 	struct iovec iov;
 	char   buf[8192];
 	struct msghdr msg = {
-		(void *)&nladdr, sizeof(nladdr),
-		&iov,	1,
-		NULL,	0,
-		0
+		.msg_name = &nladdr, .msg_namelen = sizeof(nladdr),
+		.msg_iov = &iov, .msg_iovlen = 1,
+		.msg_control = (void *)NULL, .msg_controllen = 0,
+		.msg_flags = 0
 	};
 
 	iov.iov_base = buf;
-- 
2.43.0

[iproute2, RESEND PATCH 2/2] arpd: drop useless initializers

[Dario Binacchi]

It is useless to initialize the fields of a structure to their default
values. This patch keeps the initialization only for those fields that
are not set to their default values.

Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
---
 misc/arpd.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/misc/arpd.c b/misc/arpd.c
index b4935c23eebb..a2ae76a41f8d 100644
--- a/misc/arpd.c
+++ b/misc/arpd.c
@@ -439,8 +439,6 @@ static void get_kern_msg(void)
 	struct msghdr msg = {
 		.msg_name = &nladdr, .msg_namelen = sizeof(nladdr),
 		.msg_iov = &iov, .msg_iovlen = 1,
-		.msg_control = (void *)NULL, .msg_controllen = 0,
-		.msg_flags = 0
 	};
 
 	iov.iov_base = buf;
-- 
2.43.0

Re: [iproute2, RESEND PATCH 1/2] arpd: use designated initializers for msghdr structure

[Stephen Hemminger]

On Sun, 22 Sep 2024 16:46:12 +0200
Dario Binacchi <dario.binacchi@amarulasolutions.com> wrote:

> This patch fixes the following error:
> 
> arpd.c:442:17: error: initialization of 'int' from 'void *' makes integer from pointer without a cast [-Wint-conversion]
>   442 |                 NULL,   0,
> 
> raised by Buildroot autobuilder [1].
> 
> In the case in question, the analysis of socket.h [2] containing the
> msghdr structure shows that it has been modified with the addition of
> padding fields, which cause the compilation error. The use of designated
> initializers allows the issue to be fixed.
> 
> struct msghdr {
> 	void *msg_name;
> 	socklen_t msg_namelen;
> 	struct iovec *msg_iov;
> #if __LONG_MAX > 0x7fffffff && __BYTE_ORDER == __BIG_ENDIAN
> 	int __pad1;
> #endif
> 	int msg_iovlen;
> #if __LONG_MAX > 0x7fffffff && __BYTE_ORDER == __LITTLE_ENDIAN
> 	int __pad1;
> #endif
> 	void *msg_control;
> #if __LONG_MAX > 0x7fffffff && __BYTE_ORDER == __BIG_ENDIAN
> 	int __pad2;
> #endif
> 	socklen_t msg_controllen;
> #if __LONG_MAX > 0x7fffffff && __BYTE_ORDER == __LITTLE_ENDIAN
> 	int __pad2;
> #endif
> 	int msg_flags;
> };

That is a really bad idea to put extra padding in there.

> 
> [1] http://autobuild.buildroot.org/results/e4cdfa38ae9578992f1c0ff5c4edae3cc0836e3c/
> [2] iproute2/host/mips64-buildroot-linux-musl/sysroot/usr/include/sys/socket.h
> 
> Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
> ---
>  misc/arpd.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/misc/arpd.c b/misc/arpd.c
> index e77ef53928a2..b4935c23eebb 100644
> --- a/misc/arpd.c
> +++ b/misc/arpd.c
> @@ -437,10 +437,10 @@ static void get_kern_msg(void)
>  	struct iovec iov;
>  	char   buf[8192];
>  	struct msghdr msg = {
> -		(void *)&nladdr, sizeof(nladdr),
> -		&iov,	1,
> -		NULL,	0,
> -		0
> +		.msg_name = &nladdr, .msg_namelen = sizeof(nladdr),

When converting, to named initializer, please put one per line
like other code does in iproute.

> +		.msg_iov = &iov, .msg_iovlen = 1,
> +		.msg_control = (void *)NULL, .msg_controllen = 0,

The C standard says that NULL can be used for void *, cast there 
is unnecessary.

> +		.msg_flags = 0
>  	};
>  
>  	iov.iov_base = buf;