Date: Fri, 3 Nov 2006 09:46:47 +0000 From: MQ <antinvidia@gmail.com> To: "Brooks Davis" <brooks@one-eyed-alien.net> Cc: freebsd-net@freebsd.org Subject: Re: Reentrant problem with inet_ntoa in the kernel Message-ID: <be0088ce0611030146u5e97e08cmbd36e94d772c8a94@mail.gmail.com> In-Reply-To: <20061102142543.GC70915@lor.one-eyed-alien.net> References: <be0088ce0611020026y4fe07749pd5a984f8744769b@mail.gmail.com> <20061102142543.GC70915@lor.one-eyed-alien.net>
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2006/11/2, Brooks Davis <brooks@one-eyed-alien.net>: > > On Thu, Nov 02, 2006 at 08:26:27AM +0000, . wrote: > > Hi, > > > > I am confused by the use of inet_ntoa function in the kernel. > > > > The function inet_ntoa in the /sys/libkern/inet_ntoa.c uses a static > array > > static char buf[4 * sizeof "123"]; > > to store the result. And it returns the address of the array to the > caller. > > > > I think this inet_ntoa is not reentrant, though there are several > functions > > calling it. If two functions call it simultaneously, the result will be > > corrupted. Though I haven't really encountered this situation, it may > occur > > someday, especially when using multi-processors. > > > > There is another reentrant version of inet_ntoa called inet_ntoa_r in > the > > same file. It has been there for several years, but just used by ipfw2 > for > > about four times in 7-CURRENT. In my patch, I replaced all the calls to > > inet_ntoa with calls to inet_ntoa_r. > > > > By the way, some of the original calls is written in this style: > > strcpy(buf, inet_ntoa(ip)) > > The modified code is written in this style > > inet_ntoa_r(ip, buf) > > This change avoids a call to strcpy, and can save a little time. > > > > Here is the patch. > > > http://people.freebsd.org/~delphij/misc/patch-itoa-by-nodummy-at-yeah-net > > > > I've already sent to PR(kern/104738), but got no reply, maybe it should > be > > discussed here first? > > I've got to agree with other posters that the stack variable allocations > are ugly. What about extending log and printf to understand ip4v > addresses? That's 90% of the uses and the others appears to have > buffers already. > > -- Brooks > > > Ugly? Why? Don't you use local variables in your sources? By the way, implementing a printf/log which understands ipv4 address is tedious, perhaps.
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