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[96.60.249.169]) by smtp.gmail.com with ESMTPSA id 956f58d0204a3-63f4c3cc3fdsm3663124d50.7.2025.10.28.15.56.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 28 Oct 2025 15:56:18 -0700 (PDT) Message-ID: Date: Tue, 28 Oct 2025 18:56:13 -0400 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 1/2] tools: Add adapter tool for services using sd_notify To: Alyssa Ross References: <20251003-udev-v4-0-7d7344b14d11@gmail.com> <20251003-udev-v4-1-7d7344b14d11@gmail.com> <87ms5b3uk7.fsf@alyssa.is> Content-Language: en-US From: Demi Marie Obenour Autocrypt: addr=demiobenour@gmail.com; keydata= xsFNBFp+A0oBEADffj6anl9/BHhUSxGTICeVl2tob7hPDdhHNgPR4C8xlYt5q49yB+l2nipd aq+4Gk6FZfqC825TKl7eRpUjMriwle4r3R0ydSIGcy4M6eb0IcxmuPYfbWpr/si88QKgyGSV Z7GeNW1UnzTdhYHuFlk8dBSmB1fzhEYEk0RcJqg4AKoq6/3/UorR+FaSuVwT7rqzGrTlscnT DlPWgRzrQ3jssesI7sZLm82E3pJSgaUoCdCOlL7MMPCJwI8JpPlBedRpe9tfVyfu3euTPLPx wcV3L/cfWPGSL4PofBtB8NUU6QwYiQ9Hzx4xOyn67zW73/G0Q2vPPRst8LBDqlxLjbtx/WLR 6h3nBc3eyuZ+q62HS1pJ5EvUT1vjyJ1ySrqtUXWQ4XlZyoEFUfpJxJoN0A9HCxmHGVckzTRl 5FMWo8TCniHynNXsBtDQbabt7aNEOaAJdE7to0AH3T/Bvwzcp0ZJtBk0EM6YeMLtotUut7h2 Bkg1b//r6bTBswMBXVJ5H44Qf0+eKeUg7whSC9qpYOzzrm7+0r9F5u3qF8ZTx55TJc2g656C 9a1P1MYVysLvkLvS4H+crmxA/i08Tc1h+x9RRvqba4lSzZ6/Tmt60DPM5Sc4R0nSm9BBff0N m0bSNRS8InXdO1Aq3362QKX2NOwcL5YaStwODNyZUqF7izjK4QARAQABzTxEZW1pIE1hcmll IE9iZW5vdXIgKGxvdmVyIG9mIGNvZGluZykgPGRlbWlvYmVub3VyQGdtYWlsLmNvbT7CwXgE EwECACIFAlp+A0oCGwMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJELKItV//nCLBhr8Q AK/xrb4wyi71xII2hkFBpT59ObLN+32FQT7R3lbZRjVFjc6yMUjOb1H/hJVxx+yo5gsSj5LS 9AwggioUSrcUKldfA/PKKai2mzTlUDxTcF3vKx6iMXKA6AqwAw4B57ZEJoMM6egm57TV19kz PMc879NV2nc6+elaKl+/kbVeD3qvBuEwsTe2Do3HAAdrfUG/j9erwIk6gha/Hp9yZlCnPTX+ VK+xifQqt8RtMqS5R/S8z0msJMI/ajNU03kFjOpqrYziv6OZLJ5cuKb3bZU5aoaRQRDzkFIR 6aqtFLTohTo20QywXwRa39uFaOT/0YMpNyel0kdOszFOykTEGI2u+kja35g9TkH90kkBTG+a EWttIht0Hy6YFmwjcAxisSakBuHnHuMSOiyRQLu43ej2+mDWgItLZ48Mu0C3IG1seeQDjEYP tqvyZ6bGkf2Vj+L6wLoLLIhRZxQOedqArIk/Sb2SzQYuxN44IDRt+3ZcDqsPppoKcxSyd1Ny 2tpvjYJXlfKmOYLhTWs8nwlAlSHX/c/jz/ywwf7eSvGknToo1Y0VpRtoxMaKW1nvH0OeCSVJ itfRP7YbiRVc2aNqWPCSgtqHAuVraBRbAFLKh9d2rKFB3BmynTUpc1BQLJP8+D5oNyb8Ts4x Xd3iV/uD8JLGJfYZIR7oGWFLP4uZ3tkneDfYzsFNBFp+A0oBEAC9ynZI9LU+uJkMeEJeJyQ/ 8VFkCJQPQZEsIGzOTlPnwvVna0AS86n2Z+rK7R/usYs5iJCZ55/JISWd8xD57ue0eB47bcJv VqGlObI2DEG8TwaW0O0duRhDgzMEL4t1KdRAepIESBEA/iPpI4gfUbVEIEQuqdqQyO4GAe+M kD0Hy5JH/0qgFmbaSegNTdQg5iqYjRZ3ttiswalql1/iSyv1WYeC1OAs+2BLOAT2NEggSiVO txEfgewsQtCWi8H1SoirakIfo45Hz0tk/Ad9ZWh2PvOGt97Ka85o4TLJxgJJqGEnqcFUZnJJ riwoaRIS8N2C8/nEM53jb1sH0gYddMU3QxY7dYNLIUrRKQeNkF30dK7V6JRH7pleRlf+wQcN fRAIUrNlatj9TxwivQrKnC9aIFFHEy/0mAgtrQShcMRmMgVlRoOA5B8RTulRLCmkafvwuhs6 dCxN0GNAORIVVFxjx9Vn7OqYPgwiofZ6SbEl0hgPyWBQvE85klFLZLoj7p+joDY1XNQztmfA rnJ9x+YV4igjWImINAZSlmEcYtd+xy3Li/8oeYDAqrsnrOjb+WvGhCykJk4urBog2LNtcyCj kTs7F+WeXGUo0NDhbd3Z6AyFfqeF7uJ3D5hlpX2nI9no/ugPrrTVoVZAgrrnNz0iZG2DVx46 x913pVKHl5mlYQARAQABwsFfBBgBAgAJBQJafgNKAhsMAAoJELKItV//nCLBwNIP/AiIHE8b oIqReFQyaMzxq6lE4YZCZNj65B/nkDOvodSiwfwjjVVE2V3iEzxMHbgyTCGA67+Bo/d5aQGj gn0TPtsGzelyQHipaUzEyrsceUGWYoKXYyVWKEfyh0cDfnd9diAm3VeNqchtcMpoehETH8fr RHnJdBcjf112PzQSdKC6kqU0Q196c4Vp5HDOQfNiDnTf7gZSj0BraHOByy9LEDCLhQiCmr+2 E0rW4tBtDAn2HkT9uf32ZGqJCn1O+2uVfFhGu6vPE5qkqrbSE8TG+03H8ecU2q50zgHWPdHM OBvy3EhzfAh2VmOSTcRK+tSUe/u3wdLRDPwv/DTzGI36Kgky9MsDC5gpIwNbOJP2G/q1wT1o Gkw4IXfWv2ufWiXqJ+k7HEi2N1sree7Dy9KBCqb+ca1vFhYPDJfhP75I/VnzHVssZ/rYZ9+5 1yDoUABoNdJNSGUYl+Yh9Pw9pE3Kt4EFzUlFZWbE4xKL/NPno+z4J9aWemLLszcYz/u3XnbO vUSQHSrmfOzX3cV4yfmjM5lewgSstoxGyTx2M8enslgdXhPthZlDnTnOT+C+OTsh8+m5tos8 HQjaPM01MKBiAqdPgksm1wu2DrrwUi6ChRVTUBcj6+/9IJ81H2P2gJk3Ls3AVIxIffLoY34E +MYSfkEjBz0E8CLOcAw7JIwAaeBT In-Reply-To: <87ms5b3uk7.fsf@alyssa.is> Content-Type: multipart/signed; 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boundary="------------GMjTf9onVz5jqkBhr0jjsyt5"; protected-headers="v1" From: Demi Marie Obenour To: Alyssa Ross Cc: Spectrum OS Development Message-ID: Subject: Re: [PATCH v4 1/2] tools: Add adapter tool for services using sd_notify References: <20251003-udev-v4-0-7d7344b14d11@gmail.com> <20251003-udev-v4-1-7d7344b14d11@gmail.com> <87ms5b3uk7.fsf@alyssa.is> In-Reply-To: <87ms5b3uk7.fsf@alyssa.is> Autocrypt-Gossip: addr=hi@alyssa.is; keydata= xsFNBFpSgoYBEAC4xkCYidG2JlRWulUkTWcx0pHFDf3oSbb6Q872Kb3iDChWgluNVz43hva1 3xfDo9foV0GoyfGl/ycSCkXX5hlQr7ir/5FN38E7H/yY6tH8+l68iDgIOcb1qY0OYaxyg+Lz WesfFQedrmwNTbF4L1BtWzrTR5PflDdhDo5VWSguHGJFSclchcr/6UmMb/gOUN+2ElBC2TE2 EKY099phZ6DJZ2aZCsclwKIdCpZzXlEmXPAeaH5om6xo90JYv5+sFji40R0Plqec3WC+jTxy lGca6IbPdOminuUF+GvsR86eVsgh/0XNK7/zus7gyc4PuMUA1rCoeHcWOBDPgmelgCQyJGXd /bXeKuUsGoge58uc7/YNvOh1vfpD3AaEMqAyXfmmUwBnIicml74+2eOpH3Oljfs01g+DhkOB MtpVSZSgaIDvP0WG6cbAxImoUasnmNxEDNskfVmI8bsajPW9bt4z5hiP5Q9G3vE0D5HcIFdM adOz81PpOwNiUXcjtYV1PWZQ56jbSTOf8EBvsB71WwB+XgVWcPzIlY8hAykiHIO87oV3o71U JTAn1Foj7mjSADnY0deleOmar/K5jrK3wvKKM1XlB7PXcGBdkorJC+cbxVsw0ADzMw0c7bVc wEE7OFvHjQiIK1lO+lb1cvGBBY3IZxjsjZdA/VsFHFdAeYlzNQARAQABzRpBbHlzc2EgUm9z cyA8aGlAYWx5c3NhLmlzPsLBlwQTAQgAQQIbAwULCQgHAgYVCAkKCwIEFgIDAQIeAQIXgAIZ ARYhBHVzVtd5u7iIdz5BXnNszfnvUb2XBQJoh9HmBQkOtoJgAAoJEHNszfnvUb2XFxAP/jF7 Rxuspytz7VwOA/y5WQe/FdPNRvyRUzj66ZzfuaG++md14LWcrvbb2hHLdS5ePdKoOaqC3xhK Ncy/5RVd4pD5N4AY7O5228JKDO8GGWEl3rupOCmYQL9P8GpsdGt2xkFqbu4HrFzMTzl6nvKN GtvhBSCkAW3v7wTwPf2rkjX8f+clmRZn4YLfojaBCT/ZFjmJkQSWZ+2rUZOxjgZgckLkplu8 LVILVdaHNLkOrxbKQLuuVyEkN+/YrshyJP4a7Z/Tnw+3eZcaLuLOxBHpWOAAgJZ8kL+V7BxK DlTywv/OOr0CoNi9zjH3VgRiJ1961K/DocjA50pWBilMUs4jGp9omhkAOwdNV2hi+Zj/GXaD kgvBlE313DGWzgW0RauL8j5/GULgphwm5UOHXb/5yM9pRw87kfQ/+zQuHpguoXSGkUv0kSID 88kUGlNxy1kkTsSYG2UTKLmLDPuUGOUDGaNUzD+J49MogSLTmvHUIYNs0jFmpLyhVoTtSi/I VQQpHyk9ucAZd2OLxChm3RBJhAbmGw3rhUxx6B8SHwcBcJDttGyYF2GZj9AYAGlU/Fm1Itoi NwJD0vQnSZ//25l+XJehpeeixsqydj00gksHWEFaIEgCYyC6JfmGS4HtuUcv76vc2vLCv5aH hJVHHKGs+kiKJ2+r7bCNwvW0doVePdByzjgEZyd/yxIKKwYBBAGXVQEFAQEHQCVxoiHOlsEo NDKGCbxg4nL3E1CV0MRQCU1hPowd77h3AwEIB8LBfAQYAQoAJgIbDBYhBHVzVtd5u7iIdz5B XnNszfnvUb2XBQJoh9HXBQkB4YUCAAoJEHNszfnvUb2XgvAP+gIIKR3KatmwuUcla1RN6tUc 0Ae9eqS1cbSEDj8a14fnvUHtlCEO5g4m2PvPn7L2o7047ppl5100+zGMocXWslnDFJJVeAOp xzlhZ48DFMxkZkjtLY2fRrj1tOtzrTRikV0/UsaVs9tMPMEsVu/FH0exMoNELcqEVUgcRRpd XYXC9zgDUcM4+JRH8hDOiC51JRvdkXcokAXphuCY3J996i8Ph+kg6xMqscePscvvltR68jcT HHDOiOQtzjJRKQ6BHUzYdIRixcq210sabfZGJVT+7BfHI5qiUwfoG3DXSJygviN3I/EfnSbD 6T0Ccv/G6wQPHO4Vyn+egrMOU/HUrCKuq/b0rYvI8pTtRWAxIHkFZoKVB8I8Rl8+riGiEUAh Ja0bU4iOg7vR5Bm8Gt/tR6KjClyBI5NN1M1haFgVXqZ3dsQDpBjivbDHbUsAXVsd00y0B4Ir 8muvII9eJOwbTyqcG9RJbflquPp+FPlgiy9pYj52PB0NwzLYqX0fOWU8IqQF3bWtdJIb4Zat XnfqYtJ/wCaJTU43N3+/TIdqNA4G3WbyRYsCnz/kkf1ARmxoq3r29dOl8OnNHEvB1+hBlNBk d+cLpsYdTxa63OpbNDpm/unX1sEpOYy04dL5Y8B1Xbh+rQFNySq4Ani2dl5N1OsrjgzZ+wkl k2wOTWzl7wFH --------------GMjTf9onVz5jqkBhr0jjsyt5 Content-Type: multipart/mixed; boundary="------------TmvMefs1Fycw33bfh9XM8uiT" --------------TmvMefs1Fycw33bfh9XM8uiT Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 10/28/25 11:38, Alyssa Ross wrote: > Demi Marie Obenour writes: >=20 >> This adapts programs using sd_notify for use with s6 readiness >> notification. stdin and stdout are hard-coded for simplicity. >> >> Signed-off-by: Demi Marie Obenour >> --- >> systemd readiness notification has two >> strict advantages over the s6 version: >> >> 1. It allows reliable reloading. >> 2. It allows providing a status message that the service manager >> can show in status output. >> >> s6 would actually benefit from both of these features. >> --- >> Changes since v1: >> >> - Hard-code file descriptors. >> - Run wrapper as background process. >> - Massively reduce code size. >> - Use // instead of /* */ for comments. >> - Check that the notification FD is a pipe and that the listening sock= et >> is a socket. >> - Rely on s6-ipc-socketbinder to create the listening socket. >> - Do not unlink the listening socket. >> --- >> tools/default.nix | 1 + >> tools/meson.build | 1 + >> tools/sd-notify-adapter/meson.build | 4 + >> tools/sd-notify-adapter/sd-notify-adapter.c | 114 +++++++++++++++++++= +++++++++ >> 4 files changed, 120 insertions(+) >=20 > Looks correct, so just some convention/readability things. If you're > happy with all my comments I can just change them all myself if you > prefer not to send a new version of the patch =E2=80=94 up to you. See below. I think the EAGAIN/EWOULDBLOCK checks and the MSG_DONTWAIT are good practices in general. You are correct that in this particular case they aren't needed, at least unless poll() can produce spurious wakeups. That said, if you prefer to change them feel free to do so. Making the changes on commit would be great. Saving a round of review is always a good thing. >> diff --git a/tools/sd-notify-adapter/meson.build b/tools/sd-notify-ada= pter/meson.build >> new file mode 100644 >> index 0000000000000000000000000000000000000000..6032a3a7704d49cae0655b= 43d0189444d3b15e4d >> --- /dev/null >> +++ b/tools/sd-notify-adapter/meson.build >> @@ -0,0 +1,4 @@ >> +# SPDX-License-Identifier: ISC >> +# SPDX-FileCopyrightText: 2025 Demi Marie Obenour >> + >> +executable('sd-notify-adapter', 'sd-notify-adapter.c', install: true)= >> diff --git a/tools/sd-notify-adapter/sd-notify-adapter.c b/tools/sd-no= tify-adapter/sd-notify-adapter.c >> new file mode 100644 >> index 0000000000000000000000000000000000000000..10f4e05eb602491540a792= c7fb5620d66d5bb989 >> --- /dev/null >> +++ b/tools/sd-notify-adapter/sd-notify-adapter.c >> @@ -0,0 +1,114 @@ >> +// SPDX-License-Identifier: MIT >> +// SPDX-FileCopyrightText: 2025 Demi Marie Obenour >> + >> +#define _GNU_SOURCE 1 >=20 > Like I said last time, this should be set by the build system. Good point. >> +#include >> +#include >> +#include >> +#include >> +#include >> +#include >> +#include >> +#include >> +#include >> +#include >> + >> +#include >> +#include >> +#include >> +#include >> +#include >> +#include >> +#include >> + >> +#define ARRAY_SIZE(s) (sizeof(s)/sizeof(s[0])) >> + >> +enum { >> + socket_fd, >> + notification_fd, >> +}; >> + >> +#define READY "READY=3D1" >> +#define READY_SIZE (sizeof(READY) - 1) >> + >> +static void process_notification(struct iovec *const msg) >> +{ >> + ssize_t first_recv_size =3D recv(socket_fd, msg->iov_base, msg->iov_= len, >> + MSG_DONTWAIT | MSG_TRUNC | MSG_PEEK);= >=20 > I guess it just doesn't matter either way, but my question about why > MSG_DONTWAIT from last time wasn't answered either. It's good practice to use MSG_DONTWAIT whenever it makes sense to do so. That avoids relying on sockets being in blocking or non-blocking mode. Setting the blocking mode changes the open file description, which means it can affect other processes too. So no-op in this case, but good idea in general. >> + if (first_recv_size =3D=3D -1) { >> + if (errno =3D=3D EINTR) >> + return; // signal caught >> + if (errno =3D=3D EAGAIN || errno =3D=3D EWOULDBLOCK) >> + return; // spurious wakeup >=20 > The check for these from the second recv was removed. Should this chec= k > also be removed? Is returning EAGAIN or EWOULDBLOCK here a valid thing= > for the kernel to do? In this particular case it probably isn't needed. However, many other cases *do* need the check: 1. Edge-triggered event sources. 2. Processing messages until no more are available. 3. Event sources that can produce spurious wakeups. >> + err(EXIT_FAILURE, "recv from notification socket"); >> + } >> + assert(first_recv_size >=3D 0); >=20 > Worth even checking? Would be a serious contract violation that would > break all sorts of things. Yeah, and this comes from the kernel, not from userspace. So it can't even happen as a result of a bug in this code. >> + size_t size =3D (size_t)first_recv_size; >> + if (size =3D=3D 0) >> + return; // avoid arithmetic on NULL pointer >> + if (size > msg->iov_len) { >> + msg->iov_base =3D realloc(msg->iov_base, size); >> + if (msg->iov_base =3D=3D NULL) >> + err(EXIT_FAILURE, "allocation failure"); >> + msg->iov_len =3D size; >> + } >> + ssize_t second_recv_size =3D recv(socket_fd, msg->iov_base, msg->iov= _len, >> + MSG_CMSG_CLOEXEC | MSG_TRUNC); >> + if (second_recv_size =3D=3D -1) { >> + if (errno =3D=3D EINTR) >> + return; >> + err(EXIT_FAILURE, "recv from notification socket"); >> + } >> + assert(first_recv_size =3D=3D second_recv_size); >> + for (char *next, *cursor =3D msg->iov_base, *end =3D cursor + size; >> + cursor !=3D NULL; cursor =3D (next =3D=3D NULL ? NULL : next + = 1)) { >> + next =3D memchr(cursor, '\n', (size_t)(end - cursor)); >> + size_t message_size =3D (size_t)((next =3D=3D NULL ? end : next) - = cursor); >> + if (message_size =3D=3D READY_SIZE && >> + memcmp(cursor, READY, READY_SIZE) =3D=3D 0) { >> + ssize_t write_size =3D write(notification_fd, "\n", 1); >> + if (write_size !=3D 1) >> + err(EXIT_FAILURE, "writing to notification descriptor"); >> + exit(0); >> + } >> + } >> +} >> + >> +int main(int argc, char **) >> +{ >> + if (argc !=3D 1) >> + errx(EXIT_FAILURE, "stdin is listening socket, stdout is notificati= on pipe"); >> + // Main event loop. >> + struct iovec v =3D { >> + .iov_base =3D NULL, >> + .iov_len =3D 0, >> + }; >=20 > It might be clearer for this to be a static, rather than a variable in > main that's only ever used by a function it calls. It took me a while > to figure out that it's being reused between calls (for realloc). And > then you don't need the initializer either. :) That is a good idea. I normally dislike global variables, but the disadvantages are much less severe here. 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