From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: passt.top; dmarc=none (p=none dis=none) header.from=gibson.dropbear.id.au Authentication-Results: passt.top; dkim=pass (2048-bit key; secure) header.d=gibson.dropbear.id.au header.i=@gibson.dropbear.id.au header.a=rsa-sha256 header.s=202602 header.b=Q8QJaTJE; dkim-atps=neutral Received: from mail.ozlabs.org (mail.ozlabs.org [IPv6:2404:9400:2221:ea00::3]) by passt.top (Postfix) with ESMTPS id 3531E5A0265 for ; Tue, 24 Mar 2026 03:54:12 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gibson.dropbear.id.au; s=202602; t=1774320849; bh=2SeOWg/bwJaRTDip2nGah3YL4EyGX3Bo5nh4f/1wT1E=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Q8QJaTJE75vrsQpgi9ZAVYlL/wMBH1IgJZ9f5Mj0IqCMUufKc1x8Tbt4FNSl/B1GY +JGcMUnsAPHeyHMvveXdwScIwKUZlFbXkGd34mFHFy1263vWcuDGgbgTFFn7Q/FWd+ WHJuAut89pkxy08eWCfx37x77OIYgNTvGiMGR4I1llG+JQdLul3xuqJOy58wqEQAss OhDYXtDzl2xTxwVI7cAXFA2eAiLAvlOoxX5Z9WaYuj5MJWlqT2DTMcUfhfgnrd4QqS LP8TXbwp68luNygJKL61DBHBmANMLWV+WnlCdnC2xdsBnXyqGeaxmkRGUcGhlRDZf1 rVvTywMuA/YXQ== Received: by gandalf.ozlabs.org (Postfix, from userid 1007) id 4ffvkn4PQGz4wCY; Tue, 24 Mar 2026 13:54:09 +1100 (AEDT) Date: Tue, 24 Mar 2026 13:48:16 +1100 From: David Gibson To: Laurent Vivier Subject: Re: [PATCH v4 4/5] iov: Add IOV_PUT_HEADER() and with_header() to write header data back to iov_tail Message-ID: References: <20260323143151.538673-1-lvivier@redhat.com> <20260323143151.538673-5-lvivier@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="dp8bMsuXAxJn2/1f" Content-Disposition: inline In-Reply-To: Message-ID-Hash: 3SOUKLFN7LCQXKSY57EDMXGSZWDFROP4 X-Message-ID-Hash: 3SOUKLFN7LCQXKSY57EDMXGSZWDFROP4 X-MailFrom: dgibson@gandalf.ozlabs.org X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: passt-dev@passt.top X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: --dp8bMsuXAxJn2/1f Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Mar 24, 2026 at 01:41:18PM +1100, David Gibson wrote: > On Mon, Mar 23, 2026 at 03:31:50PM +0100, Laurent Vivier wrote: > > Add iov_put_header_() and its wrapper macro IOV_PUT_HEADER() as a > > counterpart to IOV_PEEK_HEADER(). This writes header data back to an > > iov_tail after modification. If the header pointer matches the > > original iov buffer location, the data was already modified in place > > and no copy is needed. Otherwise, it copies the data back using > > iov_from_buf(). > >=20 > > Add with_header(), a for-loop macro that combines IOV_PEEK_HEADER() > > and IOV_PUT_HEADER() to allow modifying a header in place within a > > block scope. > >=20 > > Signed-off-by: Laurent Vivier > > --- > > iov.c | 22 ++++++++++++++++++++++ > > iov.h | 25 ++++++++++++++++++++++++- > > 2 files changed, 46 insertions(+), 1 deletion(-) > >=20 > > diff --git a/iov.c b/iov.c > > index 8134b8c9f988..7fc9c3c78a32 100644 > > --- a/iov.c > > +++ b/iov.c > > @@ -308,6 +308,28 @@ void *iov_peek_header_(struct iov_tail *tail, void= *v, size_t len, size_t align) > > return v; > > } > > =20 > > +/** > > + * iov_put_header_() - Write header back to an IOV tail > > + * @tail: IOV tail to write header to > > + * @v: Pointer to header data to write > > + * @len: Length of header to write, in bytes > > + * > > + * Return: number of bytes written > > + */ > > +/* cppcheck-suppress unusedFunction */ > > +size_t iov_put_header_(const struct iov_tail *tail, const void *v, siz= e_t len) > > +{ > > + size_t l =3D len; > > + > > + /* iov_peek_header_() already called iov_check_header() */ > > + if ((char *)tail->iov[0].iov_base + tail->off !=3D v) > > + l =3D iov_from_buf(tail->iov, tail->cnt, tail->off, v, len); > > + > > + assert(l =3D=3D len); > > + > > + return l; > > +} > > + > > /** > > * iov_remove_header_() - Remove a header from an IOV tail > > * @tail: IOV tail to remove header from (modified) > > diff --git a/iov.h b/iov.h > > index d295d05b3bab..4ce425ccdbe5 100644 > > --- a/iov.h > > +++ b/iov.h > > @@ -90,6 +90,7 @@ bool iov_tail_prune(struct iov_tail *tail); > > size_t iov_tail_size(struct iov_tail *tail); > > bool iov_drop_header(struct iov_tail *tail, size_t len); > > void *iov_peek_header_(struct iov_tail *tail, void *v, size_t len, siz= e_t align); > > +size_t iov_put_header_(const struct iov_tail *tail, const void *v, siz= e_t len); > > void *iov_remove_header_(struct iov_tail *tail, void *v, size_t len, s= ize_t align); > > ssize_t iov_tail_clone(struct iovec *dst_iov, size_t dst_iov_cnt, > > struct iov_tail *tail); > > @@ -112,6 +113,16 @@ ssize_t iov_tail_clone(struct iovec *dst_iov, size= _t dst_iov_cnt, > > sizeof(var_), \ > > __alignof__(var_)))) > > =20 > > +/** > > + * IOV_PUT_HEADER() - Write header back to an IOV tail > > + * @tail_: IOV tail to write header to > > + * @var_: Pointer to a variable containing the header data to write > > + * > > + * Return: number of bytes written > > + */ > > +#define IOV_PUT_HEADER(tail_, var_) \ > > + (iov_put_header_((tail_), (var_), sizeof(*var_))) > > + > > /** > > * IOV_REMOVE_HEADER() - Remove and return typed header from an IOV ta= il > > * @tail_: IOV tail to remove header from (modified) > > @@ -130,7 +141,8 @@ ssize_t iov_tail_clone(struct iovec *dst_iov, size_= t dst_iov_cnt, > > ((__typeof__(var_) *)(iov_remove_header_((tail_), &(var_), \ > > sizeof(var_), __alignof__(var_)))) > > =20 > > -/** IOV_DROP_HEADER() - Remove a typed header from an IOV tail > > +/** > > + * IOV_DROP_HEADER() - Remove a typed header from an IOV tail > > * @tail_: IOV tail to remove header from (modified) > > * @type_: Data type of the header to remove > > * > > @@ -138,4 +150,15 @@ ssize_t iov_tail_clone(struct iovec *dst_iov, size= _t dst_iov_cnt, > > */ > > #define IOV_DROP_HEADER(tail_, type_) iov_drop_header((tail_), sizeof= (type_)) > > =20 > > +/** > > + * with_header() - Execute a block on a given header > > + * @type: Data type of the header to modify >=20 > We already use __typeof__ in IOV_PEEK_HEADER(), so we should be able > to use that to avoid explicitly passing the type. >=20 > > + * @hdr_: Variable name to receive the header pointer > > + * @tail_: IOV tail to peek/put the header from/to > > + */ > > +#define with_header(type_, hdr_, tail_) \ > > + for (type_ store_, *hdr_ =3D IOV_PEEK_HEADER(tail_, store_); \ > > + hdr_; \ > > + IOV_PUT_HEADER(tail_, hdr_), hdr_ =3D NULL) > > + I know I suggested this, but looking at it now, I'm wondering if the fact that you _must not_ alter the tail in the block is too non-obvious a constraint :/. In particular this means you can never work with multiple headers at once, say: with_header(iphdr) { with_header(udphdr) { ... } } --=20 David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson --dp8bMsuXAxJn2/1f Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQIzBAEBCgAdFiEEO+dNsU4E3yXUXRK2zQJF27ox2GcFAmnB+28ACgkQzQJF27ox 2Gcqdg//fNJVxE7/rAy/Xt3Tpa0zf7V9OKFGdVQec+YMPC96amQUFEML577VBy9C 7ZE2+EV+tOqSEyY4zXv6N6HQYysfcKK21+t7M+y5Nssk3nXvKYuauy39bqOYFwJI 36sXBYvFt3d0D/gXDgcD+QKBdTp5Bfl5I8of2wCq/FpnZxiWmLGePK9a//H8R+Wn S56CejgcKnn77Y0K0lZT1oteU6Hkr4v5fEQV0RqNKbx8w71Gljwsavr+fQuBf7Ll UNYEWzhI6rI7AGNmiUnPHWF1VCDQT9IcXjmEtSxE9C+q5ir/4zNhX+WH9eU4mbE6 jFv5BhItiAS9QGBmJxKSIyVXr0zznYBJQiSVRvUF8fXPcrgBYs2JUF7Z2AMxNVIR bhiQYiKfWbmwJQoc31PaoLGXAIZcZrX/muypEuyXh4Ijd6PIDjLevR6n5WOFSBQN HLbja1QOYiaDBYvZdoY190m1OlrUNi8jvpbmsSlv378dPmXOdrcY7SgfMzLiD/Zy lSAljspjHrx464mobYpVIHTAfevd5ZDaHMaNFWhXrATxxHyz0Loy2yA86cw9YxNo hnmvmORA0c9mLYt24qOugftE185JOmw6Yc3jP1MtjPCs+p40GAeNqBmkSOOGfhoS OQG5AkIsQ46Y1KSMTtzXu2EXMXwW5kSlBTBvfc0zbiF+YbhxLbo= =QTCL -----END PGP SIGNATURE----- --dp8bMsuXAxJn2/1f--