Subversion Repositories planix.SVN

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

static uvlong order = (uvlong) 0x0001020304050607ULL;

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

        t = (uchar*)to;
        o = (uchar*)&order;
        for(i = 0; i < 8; i++)
                t[o[i]] = f[i];
}

/*
 *  After a fork with fd's copied, both fd's are pointing to
 *  the same Chan structure.  Since the offset is kept in the Chan
 *  structure, the seek's and read's in the two processes can
 *  compete at moving the offset around.  Hence the retry loop.
 *
 *  Since the bintime version doesn't need a seek, it doesn't
 *  have the loop.
 */
vlong
nsec(void)
{
        char b[12+1];
        static int f = -1;
        static int usebintime;
        int retries;
        vlong t;

        if(f < 0){
                usebintime = 1;
                f = open("/dev/bintime", OREAD|OCEXEC);
                if(f < 0){
                        usebintime = 0;
                        f = open("/dev/nsec", OREAD|OCEXEC);
                        if(f < 0)
                                return 0;
                }
        }

        if(usebintime){
                if(read(f, b, sizeof(uvlong)) < 0)
                        goto error;
                be2vlong(&t, (uchar*)b);
                return t;
        } else {
                for(retries = 0; retries < 100; retries++){
                        if(seek(f, 0, 0) >= 0 && read(f, b, sizeof(b)-1) >= 0){
                                b[sizeof(b)-1] = 0;
                                return strtoll(b, 0, 0);
                        }
                }
        }

error:
        close(f);
        f = -1;
        return 0;
}