[LEDE-DEV] [PATCH] umdns: Replace unnecessary memset calls with {}.

[rosenp at gmail.com]

On Wed, 2017-11-08 at 21:17 +0100, Arjen de Korte wrote:
> Citeren Rosen Penev <rosenp at gmail.com>:
> 
> > Less verbose.
> 
> And uses a GCC extension which makes it less portable. ISO C
> forbids  
> empty initializer braces [1]. See for yourself by adding the
> -pedantic  
> flag to your CFLAGS. The correct way to initialize to all-zeros is  
> therefore { 0 }.
> 
> [1] ISO/IEC 9899:201x, paragraph 6.7.9 Initialization, clause 21
> 
> "If there are fewer initializers in a brace-enclosed list than
> there  
> are elements or members
> of an aggregate, or fewer characters in a string literal used to  
> initialize an array of known
> size  than  there  are  elements  in  the  array,  the  remainder  of
>    
> the  aggregate  shall  be
> initialized implicitly the same as objects that have static storage
> duration."

I decided to test this with the following program.


#include <stdio.h>
#include <stdint.h>
#include <string.h>

int main()
{
        struct k {
                int h;
                int t;
        };

	struct k z = {5};
        printf("%d", z.t);

        return 0;
}

0 was printed instead of 5. 
> 
> > Signed-off-by: Rosen Penev <rosenp at gmail.com>
> > 
> > v2: some of those memset calls are needed. Also replace { 0 } with
> > {}.
> > ---
> >  interface.c | 16 ++++++----------
> >  1 file changed, 6 insertions(+), 10 deletions(-)
> > 
> > diff --git a/interface.c b/interface.c
> > index 7f814d2..deabcbb 100644
> > --- a/interface.c
> > +++ b/interface.c
> > @@ -186,7 +186,7 @@ read_socket4(struct uloop_fd *u, unsigned int
> > events)
> >  	struct iovec iov[1];
> >  	char cmsg[CMSG_SPACE(sizeof(struct in_pktinfo)) +  
> > CMSG_SPACE(sizeof(int)) + 1];
> >  	struct cmsghdr *cmsgptr;
> > -	struct msghdr msg;
> > +	struct msghdr msg = {};
> >  	socklen_t len;
> >  	struct sockaddr_in from;
> >  	int flags = 0, ifindex = -1;
> > @@ -202,7 +202,6 @@ read_socket4(struct uloop_fd *u, unsigned int
> > events)
> >  	iov[0].iov_base = buffer;
> >  	iov[0].iov_len = sizeof(buffer);
> > 
> > -	memset(&msg, 0, sizeof(msg));
> >  	msg.msg_name = (struct sockaddr *) &from;
> >  	msg.msg_namelen = sizeof(struct sockaddr_in);
> >  	msg.msg_iov = iov;
> > @@ -260,7 +259,7 @@ read_socket6(struct uloop_fd *u, unsigned int
> > events)
> >  	struct iovec iov[1];
> >  	char cmsg6[CMSG_SPACE(sizeof(struct in6_pktinfo)) +  
> > CMSG_SPACE(sizeof(int)) + 1];
> >  	struct cmsghdr *cmsgptr;
> > -	struct msghdr msg;
> > +	struct msghdr msg = {};
> >  	socklen_t len;
> >  	struct sockaddr_in6 from;
> >  	int flags = 0, ifindex = -1;
> > @@ -276,7 +275,6 @@ read_socket6(struct uloop_fd *u, unsigned int
> > events)
> >  	iov[0].iov_base = buffer;
> >  	iov[0].iov_len = sizeof(buffer);
> > 
> > -	memset(&msg, 0, sizeof(msg));
> >  	msg.msg_name = (struct sockaddr *) &from;
> >  	msg.msg_namelen = sizeof(struct sockaddr_in6);
> >  	msg.msg_iov = iov;
> > @@ -327,17 +325,16 @@ read_socket6(struct uloop_fd *u, unsigned int
> > events)
> >  static int
> >  interface_mcast_setup4(struct interface *iface)
> >  {
> > -	struct ip_mreqn mreq;
> > +	struct ip_mreqn mreq = {};
> >  	uint8_t ttl = 255;
> >  	int no = 0;
> > -	struct sockaddr_in sa = { 0 };
> > +	struct sockaddr_in sa = {};
> >  	int fd = iface->fd.fd;
> > 
> >  	sa.sin_family = AF_INET;
> >  	sa.sin_port = htons(MCAST_PORT);
> >  	inet_pton(AF_INET, MCAST_ADDR, &sa.sin_addr);
> > 
> > -	memset(&mreq, 0, sizeof(mreq));
> >  	mreq.imr_address.s_addr = iface->v4_addr.s_addr;
> >  	mreq.imr_multiaddr = sa.sin_addr;
> >  	mreq.imr_ifindex = iface->ifindex;
> > @@ -368,17 +365,16 @@ interface_mcast_setup4(struct interface
> > *iface)
> >  static int
> >  interface_socket_setup6(struct interface *iface)
> >  {
> > -	struct ipv6_mreq mreq;
> > +	struct ipv6_mreq mreq = {};
> >  	int ttl = 255;
> >  	int no = 0;
> > -	struct sockaddr_in6 sa = { 0 };
> > +	struct sockaddr_in6 sa = {};
> >  	int fd = iface->fd.fd;
> > 
> >  	sa.sin6_family = AF_INET6;
> >  	sa.sin6_port = htons(MCAST_PORT);
> >  	inet_pton(AF_INET6, MCAST_ADDR6, &sa.sin6_addr);
> > 
> > -	memset(&mreq, 0, sizeof(mreq));
> >  	mreq.ipv6mr_multiaddr = sa.sin6_addr;
> >  	mreq.ipv6mr_interface = iface->ifindex;
> 
> 
> 
> 
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