On 4/20/20 12:15 AM, Nate Karstens wrote: > The close-on-fork flag causes the file descriptor to be closed > atomically in the child process before the child process returns > from fork(). Implement this feature and provide a method to > get/set the close-on-fork flag using fcntl(2). > > This functionality was approved by the Austin Common Standards > Revision Group for inclusion in the next revision of the POSIX > standard (see issue 1318 in the Austin Group Defect Tracker). Oh well... yet another feature slowing down a critical path. > > Co-developed-by: Changli Gao <xiaosuo@xxxxxxxxx> > Signed-off-by: Changli Gao <xiaosuo@xxxxxxxxx> > Signed-off-by: Nate Karstens <nate.karstens@xxxxxxxxxx> > --- > fs/fcntl.c | 2 ++ > fs/file.c | 50 +++++++++++++++++++++++++- > include/linux/fdtable.h | 7 ++++ > include/linux/file.h | 2 ++ > include/uapi/asm-generic/fcntl.h | 5 +-- > tools/include/uapi/asm-generic/fcntl.h | 5 +-- > 6 files changed, 66 insertions(+), 5 deletions(-) > > diff --git a/fs/fcntl.c b/fs/fcntl.c > index 2e4c0fa2074b..23964abf4a1a 100644 > --- a/fs/fcntl.c > +++ b/fs/fcntl.c > @@ -335,10 +335,12 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg, > break; > case F_GETFD: > err = get_close_on_exec(fd) ? FD_CLOEXEC : 0; > + err |= get_close_on_fork(fd) ? FD_CLOFORK : 0; > break; > case F_SETFD: > err = 0; > set_close_on_exec(fd, arg & FD_CLOEXEC); > + set_close_on_fork(fd, arg & FD_CLOFORK); > break; > case F_GETFL: > err = filp->f_flags; > diff --git a/fs/file.c b/fs/file.c > index c8a4e4c86e55..de7260ba718d 100644 > --- a/fs/file.c > +++ b/fs/file.c > @@ -57,6 +57,8 @@ static void copy_fd_bitmaps(struct fdtable *nfdt, struct fdtable *ofdt, > memset((char *)nfdt->open_fds + cpy, 0, set); > memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy); > memset((char *)nfdt->close_on_exec + cpy, 0, set); > + memcpy(nfdt->close_on_fork, ofdt->close_on_fork, cpy); > + memset((char *)nfdt->close_on_fork + cpy, 0, set); > I suggest we group the two bits of a file (close_on_exec, close_on_fork) together, so that we do not have to dirty two separate cache lines. Otherwise we will add yet another cache line miss at every file opening/closing for processes with big file tables. Ie having a _single_ bitmap array, even bit for close_on_exec, odd bit for close_on_fork static inline void __set_close_on_exec(unsigned int fd, struct fdtable *fdt) { __set_bit(fd * 2, fdt->close_on_fork_exec); } static inline void __set_close_on_fork(unsigned int fd, struct fdtable *fdt) { __set_bit(fd * 2 + 1, fdt->close_on_fork_exec); } Also the F_GETFD/F_SETFD implementation must use a single function call, to not acquire the spinlock twice.