Hi Takashi, Oh yay :-( > we've received a bug report about rfkill change that was introduced in > 5.11. While the systemd-rfkill expects the same size of both read and > write, the kernel rfkill write cuts off to the old 8 bytes while read > gives 9 bytes, hence it leads the error: > https://github.com/systemd/systemd/issues/18677 > https://bugzilla.opensuse.org/show_bug.cgi?id=1183147 > As far as I understand from the log in the commit 14486c82612a, this > sounds like the intended behavior. Not really? I don't even understand why we get this behaviour. The code is this: rfkill_fop_write(): ... /* we don't need the 'hard' variable but accept it */ if (count < RFKILL_EVENT_SIZE_V1 - 1) return -EINVAL; # this is actually 7 - RFKILL_EVENT_SIZE_V1 is 8 # (and obviously we get past this if and don't get -EINVAL /* * Copy as much data as we can accept into our 'ev' buffer, * but tell userspace how much we've copied so it can determine * our API version even in a write() call, if it cares. */ count = min(count, sizeof(ev)); # sizeof(ev) should be 9 since 'ev' is the new struct if (copy_from_user(&ev, buf, count)) return -EFAULT; ... ret = 0; ... return ret ?: count; Ah, no, I see. The bug says: EDIT: above is with kernel-core-5.10.16-200.fc33.x86_64. So you've recompiled systemd with 5.11 headers, but are running against 5.10 now, where the short write really was intentional - it lets you detect that the new fields weren't handled by the kernel. If The other issue is basically this (pre-fix) systemd code: l = read(c.rfkill_fd, &event, sizeof(event)); ... if (l != RFKILL_EVENT_SIZE_V1) /* log/return error */ So ... honestly, I don't have all that much sympathy, when the uapi header explicitly says we want to be able to change the size. But I guess "no regressions" rules are hard, so ... dunno. I guess we can add a version/size ioctl and keep using 8 bytes unless you send that? johannes
