Date: Wed, 10 Sep 2025 17:26:59 +0000 From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 289441] /dev/dsp O_NONBLOCK flag effective when set by fctnl(), ineffective when set by open() Message-ID: <bug-289441-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=289441 Bug ID: 289441 Summary: /dev/dsp O_NONBLOCK flag effective when set by fctnl(), ineffective when set by open() Product: Base System Version: 14.3-RELEASE Hardware: amd64 OS: Any Status: New Severity: Affects Some People Priority: --- Component: kern Assignee: bugs@FreeBSD.org Reporter: damjan.jov@gmail.com Here, the O_NONBLOCK flag is set by the open() call, and the fcntl() with F_GETFL proves it is set, but write() will still block: ---snip--- int audio_fd, ret; audio_fd = open("/dev/dsp", O_WRONLY | O_NONBLOCK, 0); ret = fcntl(audio_fd, F_GETFL, 0); printf("flag = 0x%08x\n", ret); ret = write(audio_fd, ..., ...); ---snip--- However, if O_NONBLOCK is set by fcntl() with F_SETFL, then write() becomes non-blocking, correctly returning -1 with errno==EAGAIN when the buffer is full, instead of blocking: ---snip--- int audio_fd, ret; audio_fd = open("/dev/dsp", O_WRONLY, 0); ret = fcntl(audio_fd, F_SETFL, O_NONBLOCK); ret = fcntl(audio_fd, F_GETFL, 0); printf("flag = 0x%08x\n", ret); ret = write(audio_fd, ..., ...); ---snip--- The same value ("flag = 0x00000005") is printed out in both cases by printf(), but it is only effective in actually making write() non-blocking when set by fcntl() with F_SETFL, it does nothing when it's set by open(). Do any real applications pass O_NONBLOCK in open()? Yes, at least Wine does, in file dlls/wineoss.drv/oss.c. This could be the cause of several sound bugs with Wine on FreeBSD. -- You are receiving this mail because: You are the assignee for the bug.home | help
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