Add implementations for some of the CloudABI file descriptor system calls.

All of the CloudABI system calls that operate on file descriptors of an
arbitrary type are prefixed with fd_. This change adds wrappers for
most of these system calls around their FreeBSD equivalents.

The dup2() system call present on CloudABI deviates from POSIX, in the
sense that it can only be used to replace existing file descriptor. It
cannot be used to create new ones. The reason for this is that this is
inherently thread-unsafe. Furthermore, there is no need on CloudABI to
use fixed file descriptor numbers. File descriptors 0, 1 and 2 have no
special meaning.

This change exposes the kern_dup() through <sys/syscallsubr.h> and puts
the FDDUP_* flags in <sys/filedesc.h>. It then adds a new flag,
FDDUP_MUSTREPLACE to force that file descriptors are replaced -- not
allocated.

Differential Revision:	https://reviews.freebsd.org/D3035
Reviewed by:	mjg

1 files changed, 1 insertions, 0 deletions

diff --git a/sys/sys/syscallsubr.h b/sys/sys/syscallsubr.h
index 4ff111e..625f834 100644
--- a/sys/sys/syscallsubr.h
+++ b/sys/sys/syscallsubr.h
@@ -85,6 +85,7 @@ int	kern_clock_settime(struct thread *td, clockid_t clock_id,
 int	kern_close(struct thread *td, int fd);
 int	kern_connectat(struct thread *td, int dirfd, int fd,
 	    struct sockaddr *sa);
+int	kern_dup(struct thread *td, int flags, int old, int new);
 int	kern_execve(struct thread *td, struct image_args *args,
 	    struct mac *mac_p);
 int	kern_fchmodat(struct thread *td, int fd, char *path,