closeioproc, iocall, ioclose, iointerrupt, iodial, ioopen, ioproc, ioread, ioread9pmsg, ioreadn, iorecvfd, iosendfd, iosleep, iowrite – slave I/O processes for threaded programs

#include <u.h>
#include <libc.h>
#include <thread.h>
typedef struct Ioproc Ioproc;
Ioproc* ioproc(void);
int      ioclose(Ioproc *io, int fd);
int      iodial(Ioproc *io, char *addr, char *local, char *dir, char *cdfp);
int      ioopen(Ioproc *io, char *file, int omode);
long     ioread(Ioproc *io, int fd, void *a, long n);
int      ioread9pmsg(Ioproc *io, int fd, void *a, uint n);
long     ioreadn(Ioproc *io, int fd, void *a, long n);
int      iorecvfd(Ioproc *io, int socket);
int      iosendfd(Ioproc *io, int socket, int fd);
int      iosleep(Ioproc *io, long milli);
long     iowrite(Ioproc *io, int fd, void *a, long n);
void     iointerrupt(Ioproc *io);
void     closeioproc(Ioproc *io);
long     iocall(Ioproc *io, long (*op)(va_list *arg), ...);

These routines provide access to I/O in slave procs. Since the I/O itself is done in a slave proc, other threads in the calling proc can run while the calling thread waits for the I/O to complete.
Ioproc forks a new slave proc and returns a pointer to the Ioproc associated with it. Ioproc uses mallocz and proccreate; if either fails, it calls sysfatal rather than return an error.
Ioclose, iodial, ioopen, ioread, ioread9pmsg, ioreadn, iorecvfd, iosendfd, iosleep, and iowrite execute the similarly named library or system calls (see close(2), dial(3), open(3), read(3), fcall(3), sendfd(3), and sleep(3)) in the slave process associated with io. It is an error to execute more than one call at a time in an I/O proc.
Iointerrupt interrupts the call currently executing in the I/O proc. If no call is executing, iointerrupt is a no-op.
Closeioproc terminates the I/O proc and frees the associated Ioproc .
Iocall is a primitive that may be used to implement more slave I/O routines. Iocall arranges for op to be called in io’s proc, with arg set to the variable parameter list, returning the value that op returns.

Relay messages between two file descriptors, counting the total number of bytes seen:
int tot;
relaythread(void *v)
int *fd, n;
char buf[1024];
Ioproc *io;
fd = v;
io = ioproc();
while((n = ioread(io, fd[0], buf, sizeof buf)) > 0){
if(iowrite(io, fd[1], buf, n) != n)
sysfatal("iowrite: %r");
tot += n;
relay(int fd0, int fd1)
int fd[4];
fd[0] = fd[3] = fd0;
fd[1] = fd[2] = fd1;
threadcreate(relaythread, fd, 8192);
threadcreate(relaythread, fd+2, 8192);
The two relaythread instances are running in the same proc, so the common access to tot is safe.
Implement ioread:
static long
_ioread(va_list *arg)
int fd;
void *a;
long n;
fd = va_arg(*arg, int);
a = va_arg(*arg, void*);
n = va_arg(*arg, long);
return read(fd, a, n);
ioread(Ioproc *io, int fd, void *a, long n)
return iocall(io, _ioread, fd, a, n);


dial(3), open(3), read(3), thread(3)

Iointerrupt is currently unimplemented.
C99 disallows the use of pointers to va_list. This interface will have to change to use pointers to a structure containing a va_list.

Space Glenda