+1 here for being compliant with POSIX and other API/ABI.. with a hurt of yet another firmware size increase :-P
Thank you Marco for perfect reporting / discussion / working example / vote of this breaking change! :-) -- CeDeROM, SQ7MHZ, http://www.tomek.cedro.info On Thu, Oct 22, 2026 at 4:48 PM Marco C. <[email protected]> wrote: > > Hello all, > > This is the vote for the breaking change in > https://github.com/apache/nuttx/pull/20796, as CONTRIBUTING.md 1.13 > step 5 requires. The [DISCUSS] thread "struct pollfd with the POSIX > layout (breaking change)" got no objection. > > The change: > struct pollfd gets the POSIX layout: int fd, short events, short > revents (8 bytes). Today it is 40 bytes on a 64-bit target and 24 bytes > on a 32-bit target. The kernel fields (arg, cb, priv) and the 32-bit > event masks move to a new kernel type, struct pollfd_s, in > include/nuttx/poll.h. poll() copies the entries into kernel memory and > copies revents back. select(), ppoll(), pselect(), epoll and the system > call interface do not change. > > Reference: <poll.h> in IEEE Std 1003.1-2017 / The Open Group Base > Specifications Issue 7, 2018 edition: > https://pubs.opengroup.org/onlinepubs/9699919799.2018edition/basedefs/poll.h.html > > Why it is necessary: > - A program or library that uses the standard layout (for example the > Rust libc crate) gets its neighbouring entries overwritten by poll(). > - In flat and protected builds, the kernel writes a callback pointer > into the user array and calls it from poll_notify(), often in an > interrupt handler. In a protected build user code can change that > pointer. > - Two threads cannot poll the same array. On the ESP32-S3 this crashes > the board today (store to address 0 in pipecommon_poll()). > > Non-breaking alternative: there is none. POSIX defines struct pollfd > with these three fields only, so a program that uses the standard type > cannot get a correct result while the NuttX type keeps its extra fields. > Keeping the old layout under a new name keeps the problem. > > Quick fix: > - Applications: rebuild. Code that uses only fd, events and revents > needs no change. Print events and revents with %x, not PRIx32 > (nuttx-apps #3878, merged). > - Out-of-tree drivers: rename struct pollfd to struct pollfd_s in the > poll methods, the waiter arrays and the poll callbacks, and include > <nuttx/poll.h> if the file does not include <nuttx/fs/fs.h>. The > compiler reports every place that is not renamed. > > Tests: build and runtime logs on real hardware (RP2350, Cortex-M33, and > ESP32-S3, Xtensa LX7) are in the PR, with ostest and a test of the > layout, of poll() on standard arrays, and of two threads on one array. > > Cost: +168 bytes of code (flat build) and +48 bytes (kernel build) on > qemu-armv8a; the stack of poll() grows by 160 bytes (64-bit) or 96 > bytes (32-bit). > > The vote is open for at least 72 hours. > > [ ] +1 Accept the change > [ ] 0 No opinion > [ ] -1 Reject the change, because... > > NuttX PMC members cast binding votes. The change needs at least 4 > binding +1 votes and no binding -1 vote. > > My vote: +1 > > Regards, > Marco Casaroli
