Date: Thu, 18 Dec 2025 18:22:52 +0000 From: John Baldwin <jhb@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: 313616c4504a - stable/15 - fcntl(F_SETFL): Don't unconditionally invoke FIONBIO and FIOASYNC Message-ID: <6944467c.26fdb.761eebd7@gitrepo.freebsd.org>
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The branch stable/15 has been updated by jhb: URL: https://cgit.FreeBSD.org/src/commit/?id=313616c4504a1b97f1c0b773fa92ba8f54b7f97c commit 313616c4504a1b97f1c0b773fa92ba8f54b7f97c Author: John Baldwin <jhb@FreeBSD.org> AuthorDate: 2025-09-10 14:22:19 +0000 Commit: John Baldwin <jhb@FreeBSD.org> CommitDate: 2025-12-18 17:01:55 +0000 fcntl(F_SETFL): Don't unconditionally invoke FIONBIO and FIOASYNC Currently, F_SETFL always invokes FIONBIO and FIOASYNC ioctls on the file descriptor even if the state of the associated flag has not changed. This means that a character device driver that implements non-blocking I/O but not async I/O needs a handler for FIOASYNC that permits setting the value to 0. This also means that fcntl(fd, F_SETFL, fcntl(fd, F_GETFL)) can fail for a character device driver that does not handle both FIONBIO and FIOASYNC. These requirements are not obvious nor well documented. Instead, only invoke FIONBIO and FIOASYNC if the relevant flag changes state. This only requires a device driver to implement support for FIONBIO or FIOASYNC if it supports the corresponding flag. While here, if a request aims to toggle both F_NOBLOCK and F_ASYNC and FIOASYNC fails, pass the previous state of F_NONBLOCK to FIONBIO instead of always disabling non-blocking I/O and then possibly reverting the flag back to on in f_flags. Reviewed by: mckusick, imp, kib, emaste Differential Revision: https://reviews.freebsd.org/D52403 (cherry picked from commit 3c152a3de42a7d077e8d19159b679c3fb7572820) --- sys/kern/kern_descrip.c | 32 +++++++++++++++++++------------- 1 file changed, 19 insertions(+), 13 deletions(-) diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c index ebc82b8dc427..2e43b5ca3b97 100644 --- a/sys/kern/kern_descrip.c +++ b/sys/kern/kern_descrip.c @@ -664,20 +664,26 @@ kern_fcntl(struct thread *td, int fd, int cmd, intptr_t arg) } while (atomic_cmpset_int(&fp->f_flag, flg, tmp) == 0); got_set = tmp & ~flg; got_cleared = flg & ~tmp; - tmp = fp->f_flag & FNONBLOCK; - error = fo_ioctl(fp, FIONBIO, &tmp, td->td_ucred, td); - if (error != 0) - goto revert_f_setfl; - tmp = fp->f_flag & FASYNC; - error = fo_ioctl(fp, FIOASYNC, &tmp, td->td_ucred, td); - if (error == 0) { - fdrop(fp, td); - break; + if (((got_set | got_cleared) & FNONBLOCK) != 0) { + tmp = fp->f_flag & FNONBLOCK; + error = fo_ioctl(fp, FIONBIO, &tmp, td->td_ucred, td); + if (error != 0) + goto revert_flags; + } + if (((got_set | got_cleared) & FASYNC) != 0) { + tmp = fp->f_flag & FASYNC; + error = fo_ioctl(fp, FIOASYNC, &tmp, td->td_ucred, td); + if (error != 0) + goto revert_nonblock; + } + fdrop(fp, td); + break; +revert_nonblock: + if (((got_set | got_cleared) & FNONBLOCK) != 0) { + tmp = ~fp->f_flag & FNONBLOCK; + (void)fo_ioctl(fp, FIONBIO, &tmp, td->td_ucred, td); } - atomic_clear_int(&fp->f_flag, FNONBLOCK); - tmp = 0; - (void)fo_ioctl(fp, FIONBIO, &tmp, td->td_ucred, td); -revert_f_setfl: +revert_flags: do { tmp = flg = fp->f_flag; tmp &= ~FCNTLFLAGS;help
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