Re: misc/38993: the macros CMSG_DATA &c. should be documented

[Taylor R Campbell <campbell%mumble.net@localhost>]

The following reply was made to PR misc/38993; it has been noted by GNATS.

From: Taylor R Campbell <campbell%mumble.net@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: misc/38993: the macros CMSG_DATA &c. should be documented
Date: Sun, 3 May 2009 12:40:48 -0400

 Except for some slightly confusing example code, the requested man
 page has been added and this PR can probably be closed.
 
 I think that the code would be a little clearer if rather than
 declaring a union with an array component of dynamic size using sizeof
 to refer to the size size, it simply used:
 
        char *cmsgbuf;
        size_t cmsgsize = CMSG_SPACE(sizeof(int));
 
        if ((cmsgbuf = malloc(cmsgsize)) == NULL)
                err(1, "malloc");
        (void)memset(&msg, 0, sizeof(msg));
        msg.msg_control = cmsgbuf;
        msg.msg_controllen = cmsgsize;
 
 Since the buffer is allocated with malloc, writing a union with a
 struct cmsghdr component doesn't add anything to the alignment already
 guaranteed by malloc.  The union is a vestige of a stack-allocated
 buffer, which might without the union be unaligned.  The code without
 any union is also conciser.