Date: Thu, 2 Nov 2006 10:45:04 +0100 From: Max Laier <max@love2party.net> To: ??? <antinvidia@gmail.com> Cc: freebsd-net@freebsd.org Subject: Re: Reentrant problem with inet_ntoa in the kernel Message-ID: <200611021045.09774.max@love2party.net> In-Reply-To: <be0088ce0611020026y4fe07749pd5a984f8744769b@mail.gmail.com> References: <be0088ce0611020026y4fe07749pd5a984f8744769b@mail.gmail.com>
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--nextPart3424761.XVr6h7v6Ly Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline On Thursday 02 November 2006 09:26, . 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-n >et > > I've already sent to PR(kern/104738), but got no reply, maybe it should > be discussed here first? In general, correct IPs in logs and debugging messages are a good thing. =20 I'm not sure, however, it is a good thing to put 17 bytes of buffer space=20 on every function stack that might want to print an IP address. I think=20 it's less intrusive and equally good to have a hand full of static=20 buffers available which are given out in a round-robin fashion - as=20 attempted in ip6_sprintf. Obviously the buffer rotation needs to be=20 atomic, though. If a caller needs the result for more than logging - or=20 cares strongly - it can still allocate a private buffer and use the _r=20 version. A general replacement of all applications of inet_ntoa just=20 seems bloat. =2D-=20 /"\ Best regards, | mlaier@freebsd.org \ / Max Laier | ICQ #67774661 X http://pf4freebsd.love2party.net/ | mlaier@EFnet / \ ASCII Ribbon Campaign | Against HTML Mail and News --nextPart3424761.XVr6h7v6Ly Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.5 (FreeBSD) iD8DBQBFSb4lXyyEoT62BG0RAstnAJ9w/KjXzOkzXAzSvA55EyfBvDKRLgCfbvdq l3GZjdEUZFnCXLwde6n2FoE= =rSuh -----END PGP SIGNATURE----- --nextPart3424761.XVr6h7v6Ly--
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