Re: [9fans] a pair nec bugs

[erik quanstrom]

here's what i settled on for now.  i believe it to
be correct in all cases, but if you are sharing file
descriptors among many processes, you may have
/dev/bintime open many more times that necessary.

i put off solving other instances of fd-group private
until later, since the solution in hand is not very
satisfying.

in the future, i believe it might make sense to make
file descriptor groups, environment groups, etc. available
via /dev/fdid to allow for sharing without false sharing.

- erik
----

#include <u.h>
#include <libc.h>
#include <tos.h>

typedef struct  Nfd     Nfd;
struct Nfd {
        int     pid;
        int     fd;
};

static  void    **nsecpriv;
#define Fd      ((Nfd*)nsecpriv[0])


static uvlong order = 0x0001020304050607ULL;

static void
be2vlong(vlong *to, uchar *f)
{
        uchar *t, *o;
        int i;

        t = (uchar*)to;
        o = (uchar*)&order;
        for(i = 0; i < sizeof order; i++)
                t[o[i]] = f[i];
}

static Nfd*
getfd(void)
{
        Nfd *p;

        if(nsecpriv != nil && Fd->pid == _tos->pid)
                return Fd;
        if(nsecpriv == nil){
                /*
                 * privalloc's allocates slots on a shared
                 * basis, even though the memory slots
                 * themselves are proc-private.
                 */
                nsecpriv = privalloc();
                if(nsecpriv == nil)
                        return nil;
                *nsecpriv = p = malloc(sizeof *p);
                if(p == nil)
                        return nil;
        }else
                p = Fd;
        p->fd = -1;
        return p;
}

vlong
nsec(void)
{
        uchar b[8];
        vlong t;
        Nfd *p;

        if((p = getfd()) == nil)
                return 0;
        if(p->fd == -1){
                p->fd = open("/dev/bintime", OREAD|OCEXEC);
                p->pid = _tos->pid;
        }
        if(pread(p->fd, b, sizeof b, 0) == sizeof b){
                be2vlong(&t, b);
                return t;
        }
        return 0;
}