Date: Tue, 26 Jan 2010 11:40:50 -0500 From: John Baldwin <jhb@freebsd.org> To: d@delphij.net Cc: delphij@freebsd.org, freebsd-net@freebsd.org, Robert Watson <rwatson@freebsd.org> Subject: Re: [PATCH] Interface description Message-ID: <201001261140.51006.jhb@freebsd.org> In-Reply-To: <4B5E16DB.2080203@delphij.net> References: <4B5E16DB.2080203@delphij.net>
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On Monday 25 January 2010 5:10:35 pm Xin LI wrote:
> Hi,
>
> I have revised the patchset based on feedback received. This version:
>
> - Unbreak the case when libpcap is being built for pre-ifdescr world.
> - Documents the descr and -descr primitives for ifconfig(8), they are
> intended for OpenBSD compatibility.
> - Simplify and concentrate memory allocation in ifconfig(8)
> - Document the use of nul terminated buffer and the meaning of length
> parameter
> - Use char* instead of sbuf and simplify the logic in kernel part.
>
> Hopefully this version would address all problems raised by reviewers.
> Comments?
I just have two suggestions/comments:
@@ -295,6 +295,7 @@ struct ifreq {
struct sockaddr ifru_addr;
struct sockaddr ifru_dstaddr;
struct sockaddr ifru_broadaddr;
+ struct { size_t length; caddr_t buffer; } ifru_buffer;
short ifru_flags[2];
short ifru_index;
int ifru_jid;
I prefer to not have this all on one line, but to instead be:
struct sockaddr ifru_addr;
struct sockaddr ifru_dstaddr;
struct sockaddr ifru_broadaddr;
struct {
size_t length;
caddr_t buffer;
} ifru_buffer;
Even better would be to actually define a separate type earlier
in the file I think:
struct ifreq_buffer {
void *buffer;
size_t length;
};
and then just use:
struct ifreq_buffer ifru_buffer;
I think caddr_t is deprecated in favor of void * for new APIs at least.
Second, it would be nice if SIOCGIFDESCR provided length feedback to userland
similar to sysctl(3). Maybe change the code to set ifr.ifr_buffer.length to
the required length when returning ENAMETOOLONG. Userland can then just skip
to that length directly, or instead use an idiom similar to sysctl where it
does the following:
ifr.ifr_buffer.buffer = NULL;
ifr.ifr_buffer.length = 0;
for (;;) {
if (ioctl(s, SIOCGIFDESCR, &ifr) == 0) {
/* have descr in ifr.ifr_buffer.buffer */
} else if (errno == ENAMETOOLONG) {
ifr.ifr_buffer.buffer = reallocf(ifr.ifr_buffer.buffer,
ifr.ifr_buffer.length);
if (ifr.ifr_buffer.buffer == NULL) {
/* handle realloc() failure, break */
}
continue;
} else {
/* handle error, break */
}
}
--
John Baldwin
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