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([2a01:e0a:e10:ef90:4326:a36e:a7cb:624b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48711764509sm30401965e9.13.2026.03.24.00.16.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 24 Mar 2026 00:16:51 -0700 (PDT) Message-ID: <0ca2db00-8982-46dc-b49e-15787720878e@redhat.com> Date: Tue, 24 Mar 2026 08:16:50 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 4/5] iov: Add IOV_PUT_HEADER() and with_header() to write header data back to iov_tail To: David Gibson References: <20260323143151.538673-1-lvivier@redhat.com> <20260323143151.538673-5-lvivier@redhat.com> From: Laurent Vivier Autocrypt: addr=lvivier@redhat.com; keydata= xsFNBFYFJhkBEAC2me7w2+RizYOKZM+vZCx69GTewOwqzHrrHSG07MUAxJ6AY29/+HYf6EY2 WoeuLWDmXE7A3oJoIsRecD6BXHTb0OYS20lS608anr3B0xn5g0BX7es9Mw+hV/pL+63EOCVm SUVTEQwbGQN62guOKnJJJfphbbv82glIC/Ei4Ky8BwZkUuXd7d5NFJKC9/GDrbWdj75cDNQx UZ9XXbXEKY9MHX83Uy7JFoiFDMOVHn55HnncflUncO0zDzY7CxFeQFwYRbsCXOUL9yBtqLer Ky8/yjBskIlNrp0uQSt9LMoMsdSjYLYhvk1StsNPg74+s4u0Q6z45+l8RAsgLw5OLtTa+ePM JyS7OIGNYxAX6eZk1+91a6tnqfyPcMbduxyBaYXn94HUG162BeuyBkbNoIDkB7pCByed1A7q q9/FbuTDwgVGVLYthYSfTtN0Y60OgNkWCMtFwKxRaXt1WFA5ceqinN/XkgA+vf2Ch72zBkJL RBIhfOPFv5f2Hkkj0MvsUXpOWaOjatiu0fpPo6Hw14UEpywke1zN4NKubApQOlNKZZC4hu6/ 8pv2t4HRi7s0K88jQYBRPObjrN5+owtI51xMaYzvPitHQ2053LmgsOdN9EKOqZeHAYG2SmRW LOxYWKX14YkZI5j/TXfKlTpwSMvXho+efN4kgFvFmP6WT+tPnwARAQABzSNMYXVyZW50IFZp dmllciA8bHZpdmllckByZWRoYXQuY29tPsLBeAQTAQIAIgUCVgVQgAIbAwYLCQgHAwIGFQgC CQoLBBYCAwECHgECF4AACgkQ8ww4vT8vvjwpgg//fSGy0Rs/t8cPFuzoY1cex4limJQfReLr SJXCANg9NOWy/bFK5wunj+h/RCFxIFhZcyXveurkBwYikDPUrBoBRoOJY/BHK0iZo7/WQkur 6H5losVZtrotmKOGnP/lJYZ3H6OWvXzdz8LL5hb3TvGOP68K8Bn8UsIaZJoeiKhaNR0sOJyI YYbgFQPWMHfVwHD/U+/gqRhD7apVysxv5by/pKDln1I5v0cRRH6hd8M8oXgKhF2+rAOL7gvh jEHSSWKUlMjC7YwwjSZmUkL+TQyE18e2XBk85X8Da3FznrLiHZFHQ/NzETYxRjnOzD7/kOVy gKD/o7asyWQVU65mh/ECrtjfhtCBSYmIIVkopoLaVJ/kEbVJQegT2P6NgERC/31kmTF69vn8 uQyW11Hk8tyubicByL3/XVBrq4jZdJW3cePNJbTNaT0d/bjMg5zCWHbMErUib2Nellnbg6bc 2HLDe0NLVPuRZhHUHM9hO/JNnHfvgiRQDh6loNOUnm9Iw2YiVgZNnT4soUehMZ7au8PwSl4I KYE4ulJ8RRiydN7fES3IZWmOPlyskp1QMQBD/w16o+lEtY6HSFEzsK3o0vuBRBVp2WKnssVH qeeV01ZHw0bvWKjxVNOksP98eJfWLfV9l9e7s6TaAeySKRRubtJ+21PRuYAxKsaueBfUE7ZT 7zfOwU0EVgUmGQEQALxSQRbl/QOnmssVDxWhHM5TGxl7oLNJms2zmBpcmlrIsn8nNz0rRyxT 460k2niaTwowSRK8KWVDeAW6ZAaWiYjLlTunoKwvF8vP3JyWpBz0diTxL5o+xpvy/Q6YU3BN efdq8Vy3rFsxgW7mMSrI/CxJ667y8ot5DVugeS2NyHfmZlPGE0Nsy7hlebS4liisXOrN3jFz asKyUws3VXek4V65lHwB23BVzsnFMn/bw/rPliqXGcwl8CoJu8dSyrCcd1Ibs0/Inq9S9+t0 VmWiQWfQkz4rvEeTQkp/VfgZ6z98JRW7S6l6eophoWs0/ZyRfOm+QVSqRfFZdxdP2PlGeIFM C3fXJgygXJkFPyWkVElr76JTbtSHsGWbt6xUlYHKXWo+xf9WgtLeby3cfSkEchACrxDrQpj+ Jt/JFP+q997dybkyZ5IoHWuPkn7uZGBrKIHmBunTco1+cKSuRiSCYpBIXZMHCzPgVDjk4viP brV9NwRkmaOxVvye0vctJeWvJ6KA7NoAURplIGCqkCRwg0MmLrfoZnK/gRqVJ/f6adhU1oo6 z4p2/z3PemA0C0ANatgHgBb90cd16AUxpdEQmOCmdNnNJF/3Zt3inzF+NFzHoM5Vwq6rc1JP jfC3oqRLJzqAEHBDjQFlqNR3IFCIAo4SYQRBdAHBCzkM4rWyRhuVABEBAAHCwV8EGAECAAkF AlYFJhkCGwwACgkQ8ww4vT8vvjwg9w//VQrcnVg3TsjEybxDEUBm8dBmnKqcnTBFmxN5FFtI WlEuY8+YMiWRykd8Ln9RJ/98/ghABHz9TN8TRo2b6WimV64FmlVn17Ri6FgFU3xNt9TTEChq AcNg88eYryKsYpFwegGpwUlaUaaGh1m9OrTzcQy+klVfZWaVJ9Nw0keoGRGb8j4XjVpL8+2x OhXKrM1fzzb8JtAuSbuzZSQPDwQEI5CKKxp7zf76J21YeRrEW4WDznPyVcDTa+tz++q2S/Bp P4W98bXCBIuQgs2m+OflERv5c3Ojldp04/S4NEjXEYRWdiCxN7ca5iPml5gLtuvhJMSy36gl U6IW9kn30IWuSoBpTkgV7rLUEhh9Ms82VWW/h2TxL8enfx40PrfbDtWwqRID3WY8jLrjKfTd R3LW8BnUDNkG+c4FzvvGUs8AvuqxxyHbXAfDx9o/jXfPHVRmJVhSmd+hC3mcQ+4iX5bBPBPM oDqSoLt5w9GoQQ6gDVP2ZjTWqwSRMLzNr37rJjZ1pt0DCMMTbiYIUcrhX8eveCJtY7NGWNyx FCRkhxRuGcpwPmRVDwOl39MB3iTsRighiMnijkbLXiKoJ5CDVvX5yicNqYJPKh5MFXN1bvsB kmYiStMRbrD0HoY1kx5/VozBtc70OU0EB8Wrv9hZD+Ofp0T3KOr1RUHvCZoLURfFhSQ= In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: mm7tgE5TT2iXxJGV74tWqVFUrPFWhLEr1SrQD6PPBVk_1774336612 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Message-ID-Hash: FIDVFWVARSRCUSZXBWTZ2YC37F724SYQ X-Message-ID-Hash: FIDVFWVARSRCUSZXBWTZ2YC37F724SYQ X-MailFrom: lvivier@redhat.com 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: On 3/24/26 03:41, 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(). >> >> 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. >> >> Signed-off-by: Laurent Vivier >> --- >> iov.c | 22 ++++++++++++++++++++++ >> iov.h | 25 ++++++++++++++++++++++++- >> 2 files changed, 46 insertions(+), 1 deletion(-) >> >> 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; >> } >> >> +/** >> + * 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, size_t len) >> +{ >> + size_t l = len; >> + >> + /* iov_peek_header_() already called iov_check_header() */ >> + if ((char *)tail->iov[0].iov_base + tail->off != v) >> + l = iov_from_buf(tail->iov, tail->cnt, tail->off, v, len); >> + >> + assert(l == 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, size_t align); >> +size_t iov_put_header_(const struct iov_tail *tail, const void *v, size_t len); >> void *iov_remove_header_(struct iov_tail *tail, void *v, size_t len, size_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_)))) >> >> +/** >> + * 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 tail >> * @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_)))) >> >> -/** 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_)) >> >> +/** >> + * with_header() - Execute a block on a given header >> + * @type: Data type of the header to modify > > We already use __typeof__ in IOV_PEEK_HEADER(), so we should be able > to use that to avoid explicitly passing the type. I tried but it's not possible to put a declaration and an initialization in the first part of the for(). for instance #define with_header(hdr_, tail_)\ for (__typeof__(*hdr_) store_, hdr_ = IOV_PEEK_HEADER(tail_, store_);\ hdr_;\ IOV_PUT_HEADER(tail_, hdr_), hdr_ = NULL) Then : struct ethhdr *eh; struct iov_tail *tail; with_header(eh, tail) becomes: for (struct ethhdr store_, eh = IOV_PEEK_HEADER(tail, store_); eh; IOV_PUT_HEADER(store, eh), eh = NULL) And struct ethhdr store_, eh = IOV_PEEK_HEADER(tail, store_); declares store_, but also declares eh, that is already declared. We could do something like: #define with_header(hdr_, tail_)\ for (__typeof__(*hdr_) store_, *tmp_hdr_ = (hdr_ = IOV_PEEK_HEADER(tail_, store_));\ hdr_;\ IOV_PUT_HEADER(tail_, hdr_), hdr_ = NULL) But I preferred to introduce the type rather than a dummy variable. Moreover, doing as I did, the variable is local to the body of the for() and cannot be used outside. Thanks, Laurent > >> + * @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_ = IOV_PEEK_HEADER(tail_, store_); \ >> + hdr_; \ >> + IOV_PUT_HEADER(tail_, hdr_), hdr_ = NULL) >> + >> #endif /* IOVEC_H */ >> -- >> 2.53.0 >> >