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([2a01:e0a:e10:ef90:343a:68f:2e91:95c]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4356997df75sm36388468f8f.29.2026.01.21.04.18.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 21 Jan 2026 04:18:35 -0800 (PST) Message-ID: <887bdb7b-ee0e-4723-889f-a90f158d0073@redhat.com> Date: Wed, 21 Jan 2026 13:18:34 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/3] tcp: Register fds with epoll at flow creation To: Stefano Brivio References: <20260119161915.4014677-1-lvivier@redhat.com> <20260119161915.4014677-3-lvivier@redhat.com> <20260121091321.22fbb246@elisabeth> <20260121124113.56147c36@elisabeth> 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: <20260121124113.56147c36@elisabeth> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: B7l9_gMsPdRdifdZBqjFyWoeUaQCAJwB3XGwfXPSGB8_1768997917 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: MWMEPQCQFW7N7I4YXKXA44LJKU442MKM X-Message-ID-Hash: MWMEPQCQFW7N7I4YXKXA44LJKU442MKM 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, David Gibson 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 1/21/26 12:41, Stefano Brivio wrote: > On Wed, 21 Jan 2026 09:43:55 +0100 > Laurent Vivier wrote: > >> On 1/21/26 09:13, Stefano Brivio wrote: >>> On Mon, 19 Jan 2026 17:19:14 +0100 >>> Laurent Vivier wrote: >>> >>>> Register connection sockets with epoll using empty events >>>> (events=0) in tcp_conn_from_tap(), tcp_tap_conn_from_sock() >>>> and tcp_flow_repair_socket(). >>>> >>>> This allows tcp_epoll_ctl() to always use EPOLL_CTL_MOD, removing >>>> the need to check whether fds are already registered. As a result, the >>>> conditional ADD/MOD logic is no longer needed, simplifying the function. >>>> >>>> Signed-off-by: Laurent Vivier >>>> --- >>>> flow.c | 1 + >>>> tcp.c | 46 ++++++++++++++++++++++++---------------------- >>>> 2 files changed, 25 insertions(+), 22 deletions(-) >>>> >>>> diff --git a/flow.c b/flow.c >>>> index cefe6c8b5b24..532339ce7fe1 100644 >>>> --- a/flow.c >>>> +++ b/flow.c >>>> @@ -357,6 +357,7 @@ static void flow_set_state(struct flow_common *f, enum flow_state state) >>>> * >>>> * Return: true if flow is registered with epoll, false otherwise >>>> */ >>>> +/* cppcheck-suppress unusedFunction */ >>>> bool flow_in_epoll(const struct flow_common *f) >>>> { >>>> return f->epollid != EPOLLFD_ID_INVALID; >>>> diff --git a/tcp.c b/tcp.c >>>> index 1db861705ddb..29d69354bd94 100644 >>>> --- a/tcp.c >>>> +++ b/tcp.c >>>> @@ -528,37 +528,22 @@ static uint32_t tcp_conn_epoll_events(uint8_t events, uint8_t conn_flags) >>>> static int tcp_epoll_ctl(struct tcp_tap_conn *conn) >>>> { >>>> uint32_t events; >>>> - int m; >>>> >>>> if (conn->events == CLOSED) { >>>> - if (flow_in_epoll(&conn->f)) { >>>> - int epollfd = flow_epollfd(&conn->f); >>>> + int epollfd = flow_epollfd(&conn->f); >>>> >>>> - epoll_del(epollfd, conn->sock); >>>> - if (conn->timer != -1) >>>> - epoll_del(epollfd, conn->timer); >>>> - } >>>> + epoll_del(epollfd, conn->sock); >>>> + if (conn->timer != -1) >>>> + epoll_del(epollfd, conn->timer); >>>> >>>> return 0; >>>> } >>>> >>>> events = tcp_conn_epoll_events(conn->events, conn->flags); >>>> >>>> - if (flow_in_epoll(&conn->f)) { >>>> - m = EPOLL_CTL_MOD; >>>> - } else { >>>> - flow_epollid_set(&conn->f, EPOLLFD_ID_DEFAULT); >>>> - m = EPOLL_CTL_ADD; >>>> - } >>>> - >>>> - if (flow_epoll_set(&conn->f, m, events, conn->sock, >>>> - !TAPSIDE(conn)) < 0) { >>>> - int ret = -errno; >>>> - >>>> - if (m == EPOLL_CTL_ADD) >>>> - flow_epollid_clear(&conn->f); >>>> - return ret; >>>> - } >>>> + if (flow_epoll_set(&conn->f, EPOLL_CTL_MOD, events, conn->sock, >>>> + !TAPSIDE(conn)) < 0) >>>> + return -errno; >>>> >>>> return 0; >>>> } >>>> @@ -1710,6 +1695,11 @@ static void tcp_conn_from_tap(const struct ctx *c, sa_family_t af, >>>> conn->sock = s; >>>> conn->timer = -1; >>>> conn->listening_sock = -1; >>>> + flow_epollid_set(&conn->f, EPOLLFD_ID_DEFAULT); >>>> + if (flow_epoll_set(&conn->f, EPOLL_CTL_ADD, 0, s, TGTSIDE) < 0) { >>>> + flow_perror(flow, "Can't register with epoll"); >>>> + goto cancel; >>>> + } >>>> conn_event(c, conn, TAP_SYN_RCVD); >>>> >>>> conn->wnd_to_tap = WINDOW_DEFAULT; >>>> @@ -2433,6 +2423,15 @@ static void tcp_tap_conn_from_sock(const struct ctx *c, union flow *flow, >>>> conn->sock = s; >>>> conn->timer = -1; >>>> conn->ws_to_tap = conn->ws_from_tap = 0; >>>> + >>>> + flow_epollid_set(&conn->f, EPOLLFD_ID_DEFAULT); >>>> + if (flow_epoll_set(&conn->f, EPOLL_CTL_ADD, 0, s, INISIDE) < 0) { >>>> + flow_perror(flow, "Can't register with epoll"); >>>> + conn_flag(c, conn, CLOSING); >>>> + FLOW_ACTIVATE(conn); >>>> + return; >>>> + } >>>> + >>>> conn_event(c, conn, SOCK_ACCEPTED); >>>> >>>> hash = flow_hash_insert(c, TAP_SIDX(conn)); >>>> @@ -3825,6 +3824,9 @@ int tcp_flow_migrate_target(struct ctx *c, int fd) >>>> return 0; >>>> } >>>> >>>> + flow_epollid_set(&conn->f, EPOLLFD_ID_DEFAULT); >>>> + flow_epoll_set(&conn->f, EPOLL_CTL_ADD, 0, conn->sock, !TAPSIDE(conn)); >>> >>> Oops, I overlooked this, because I missed re-checking on v2 after David >>> pointed it out: this causes Coverity Scan to (reasonably, I think) >>> complain that: >>> >>> /home/sbrivio/passt/tcp.c:3693:2: >>> Type: Unchecked return value (CHECKED_RETURN) >>> >>> /home/sbrivio/passt/tcp.c:3648:2: Unchecked call to function >>> 1. path: Condition "!(flow = flow_alloc())", taking false branch. >>> /home/sbrivio/passt/tcp.c:3653:2: >>> 2. path: Condition "read_all_buf(fd, &t, 112UL /* sizeof (t) */)", taking false branch. >>> /home/sbrivio/passt/tcp.c:3685:2: >>> 3. path: Condition "rc = tcp_flow_repair_socket(c, conn)", taking false branch. >>> /home/sbrivio/passt/tcp.c:3693:2: >>> 4. path: Condition "!(conn->f.pif[1] == PIF_TAP)", taking true branch. >>> /home/sbrivio/passt/tcp.c:3693:2: >>> 5. check_return: Calling "flow_epoll_set" without checking return value (as is done elsewhere 6 out of 7 times). >>> /home/sbrivio/passt/icmp.c:213:2: Examples where return value from this function is checked >>> 6. example_checked: Example 1: "flow_epoll_set(&pingf->f, 1, EPOLLIN, pingf->sock, 1U)" has its value checked in "flow_epoll_set(&pingf->f, 1, EPOLLIN, pingf->sock, 1U) < 0". >>> /home/sbrivio/passt/tcp.c:1695:2: Examples where return value from this function is checked >>> 7. example_checked: Example 2: "flow_epoll_set(&conn->f, 1, 0U, s, 1U)" has its value checked in "flow_epoll_set(&conn->f, 1, 0U, s, 1U) < 0". >>> /home/sbrivio/passt/tcp_splice.c:364:2: Examples where return value from this function is checked >>> 8. example_checked: Example 3: "flow_epoll_set(&conn->f, 1, 0U, conn->s[1], 1U)" has its value checked in "flow_epoll_set(&conn->f, 1, 0U, conn->s[1], 1U)". >>> /home/sbrivio/passt/tcp_splice.c:364:2: Examples where return value from this function is checked >>> 9. example_checked: Example 4: "flow_epoll_set(&conn->f, 1, 0U, conn->s[0], 0U)" has its value checked in "flow_epoll_set(&conn->f, 1, 0U, conn->s[0], 0U)". >>> /home/sbrivio/passt/udp_flow.c:87:2: Examples where return value from this function is checked >>> 10. example_checked: Example 5: "flow_epoll_set(&uflow->f, 1, EPOLLIN, s, sidei)" has its value checked in "flow_epoll_set(&uflow->f, 1, EPOLLIN, s, sidei) < 0". >>> >>> I don't think it's overly problematic but epoll_ctl() can, in theory, >>> fail regardless of the arguments. >>> >> >> Yes, I agree, but the problem is catched later by tcp_epoll_ctl() within >> tcp_flow_migrate_target_ext(). > > I see. It's just not really obvious, and other than that it adds static > checkers noise that I'm trying to keep to a minimum. > >> Furthermore, at this point, to handle the error we have to return 0 (single point of >> failure) and still execute FLOW_ACTIVATE() anyway. The result is therefore identical (only >> flow_hash_insert() is not executed in the absence of an error). > > Well, not calling flow_hash_insert() in that case looks like a > substantial simplification (for auditing / debugging purposes) to me. > > Given that we already have an early return above on failures from > tcp_flow_repair_socket(), maybe that could become an 'out' goto label at > the end, and we would have a similar comment for this other case? > > I'll send a patch in this sense in a bit, unless you see something > wrong with it. > Yes, that makes sense. Go ahead. Thanks, Laurent