Date: Sat, 4 Nov 2006 02:46:30 +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: <be0088ce0611031846l469b096bl536fec1d243da13f@mail.gmail.com> In-Reply-To: <20061103141732.GA87515@lor.one-eyed-alien.net> References: <be0088ce0611020026y4fe07749pd5a984f8744769b@mail.gmail.com> <20061102142543.GC70915@lor.one-eyed-alien.net> <be0088ce0611030146u5e97e08cmbd36e94d772c8a94@mail.gmail.com> <20061103141732.GA87515@lor.one-eyed-alien.net>
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2006/11/3, Brooks Davis <brooks@one-eyed-alien.net>: > > On Fri, Nov 03, 2006 at 09:46:47AM +0000, MQ wrote: > > 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? > > The particular definition used is excedingly ugly. At a minimum there > needs to be a define or a constant "16" for the lenght rather than the > 4*sizeof("123") nonsense. > > -- Brooks > > > Oh, I see. This kind of definition is really annoying, and hard to keep all the occurrences consistent. Maybe a better way is use a macro to make that clear? #define IPV4_ADDRSZ (4 * sizeof "123") char buf[IPV4_ADDRSZ]; This "ugly" definition comes from inet_ntoa() in /sys/libkern/inet_ntoa.c, I just copied the style without too much consideration, it's my fault.
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