From mboxrd@z Thu Jan 1 00:00:00 1970 From: Evgeniy Polyakov Subject: Re: [Fwd: Re: connector is missing in 2.6.12-rc2-mm1] Date: Mon, 11 Apr 2005 15:19:53 +0400 Message-ID: <1113218393.16303.13.camel@uganda> References: <1112942924.28858.234.camel@uganda> <20050410143205.18bff80d@zanzibar.2ka.mipt.ru> <1113131325.6994.66.camel@localhost.localdomain> <20050410153757.104fe611@zanzibar.2ka.mipt.ru> <20050410121005.GF26731@postel.suug.ch> <20050410161549.3abe4778@zanzibar.2ka.mipt.ru> <1113143959.1089.316.camel@jzny.localdomain> <20050410192727.GI26731@postel.suug.ch> <20050411092228.A32699@2ka.mipt.ru> <20050411104550.GK26731@postel.suug.ch> Reply-To: johnpol@2ka.mipt.ru Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="=-vzWhPJXCUTTEheqMzsZW" Cc: jamal , Kay Sievers , Herbert Xu , jmorris@redhat.com, ijc@hellion.org.uk, guillaume.thouvenin@bull.net, greg@kroah.com, linux-kernel@vger.kernel.org, akpm@osdl.org, netdev Return-path: To: Thomas Graf In-Reply-To: <20050411104550.GK26731@postel.suug.ch> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org --=-vzWhPJXCUTTEheqMzsZW Content-Type: text/plain Content-Transfer-Encoding: quoted-printable On Mon, 2005-04-11 at 12:45 +0200, Thomas Graf wrote: > * Evgeniy Polyakov <20050411092228.A32699@2ka.mipt.ru> 2005-04-11 09:22 > > On Sun, Apr 10, 2005 at 09:27:27PM +0200, Thomas Graf (tgraf@suug.ch) w= rote: > > > + size =3D NLMSG_SPACE(sizeof(*msg) + msg->len); > > > + > > > + skb =3D alloc_skb(size, GFP_ATOMIC); > > > + if (!skb) { > > > + printk(KERN_ERR "Failed to allocate new skb with size= =3D%u.\n", size); > > > + return; > > > + } > > > + > > > + nlh =3D NLMSG_PUT(skb, 0, msg->seq, NLMSG_DONE, size - sizeof= (*nlh)); > > >=20 > > > This is not correct, what happens is: > > > size =3D NLMSG_SPACE(sizeof(*msg) + msg->len); > > > --> align(hdr)+align(data) > > > size - sizeof(*nlh) > > > --> (align(hdr)-hdr)+align(data) > > > NLMSG_PUT pads again to get to the end of the data block (NLMSG_LENGT= H) > > > --> align(hdr)+(align(hdr)-hdr)+align(data) > > >=20 > > > At the moment align(hdr) =3D=3D hdr since nlmsghdr is already aligned > > > but this might change and your code will break. > >=20 > > As far as I remember, header is always supposed to be aligned properly > > "by design", so it even could be nonaligned here. >=20 > No, have a look at the macros: >=20 > #define NLMSG_LENGTH(len) ((len)+NLMSG_ALIGN(sizeof(struct nlmsghdr))) > #define NLMSG_SPACE(len) NLMSG_ALIGN(NLMSG_LENGTH(len)) >=20 > NLMSG_LENGTH points to the end of the payload in the message, NLMSG_SPACE > represents the total size aligned properly for a possible next multipart > message. >=20 > It is unlikely that nlmsghdr will ever be unaligned but there can be no > reason to introduce code that can break with perfectly legal changes just > because of that. But NLMSG_ALIGN(sizeof(hdr)) is always equal to sizeof(hdr), that size was select not accidentally. I will change it, no problem, it is good from aesthetic point of view. --=20 Evgeniy Polyakov Crash is better than data corruption -- Arthur Grabowski --=-vzWhPJXCUTTEheqMzsZW Content-Type: application/pgp-signature; name=signature.asc Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.6 (GNU/Linux) iD8DBQBCWl1ZIKTPhE+8wY0RAktFAJwOb5Pr2YO1WXRGX0k0MmT22wij2QCfboNE FqAh2pJaYdFCilvLbPwvVhc= =8sSt -----END PGP SIGNATURE----- --=-vzWhPJXCUTTEheqMzsZW--