source: trunk/athena/bin/discuss/libds/tmem.c @ 23051

/*
 *
 *      Copyright (C) 1988, 1989 by the Massachusetts Institute of Technology
 *      Developed by the MIT Student Information Processing Board (SIPB).
 *      For copying information, see the file mit-copyright.h in this release.
 *
 */
/*
 *      $Id: tmem.c,v 1.7 1999-01-22 23:10:02 ghudson Exp $
 *
 *      tfile module for ``memory'' tfiles. 
 * 
 */

#ifndef lint
static char rcsid_tmem_c[] =
    "$Id: tmem.c,v 1.7 1999-01-22 23:10:02 ghudson Exp $";
#endif /* lint */

#include <errno.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/uio.h>
#include <discuss/tfile.h>

#define min(x,y) ((x)<(y)?(x):(y))

enum iovdir { SCATTER, GATHER };
        
static int iovmove (direct, iovpp, buf, len)
        register enum iovdir direct;
        struct iovec **iovpp;
        register char *buf;
        register int len;       
{
        register int moved = 0;
        register int count;
        register struct iovec *iovp;
        
        iovp = *iovpp;
        while (len > 0) {
                count = min (iovp->iov_len, len);
                if (direct == SCATTER) 
                        memcpy (iovp->iov_base, buf, count);
                else
                        memcpy (buf, iovp->iov_base,  count);
                len -= count;
                moved += count;
                buf += count;
                iovp->iov_base = (char *)iovp->iov_base + count;
                iovp->iov_len -= count;
                if (iovp->iov_len == 0) {
                        iovp ++;
                        if (iovp->iov_len == 0)
                                break;
                }
        }
        *iovpp = iovp;
        return moved;
}

static int tmem(op, infop, info, argp, argn, result)
        int op, argn;
        register int *result, *info;
        char **infop, *argp;
{
        *result = 0;            /* optimist */
        switch (op) {
        case TFOPEN:
        case TFCLOSE:
                return 0;
        case TFREAD:
                return iovmove (GATHER, (struct iovec **)infop,
                                argp, argn);
        case TFWRITE:
                return iovmove (SCATTER, (struct iovec **)infop,
                                argp, argn);
        case TFDESTROY:
                if (*info)
                        free (*infop);
                return 0;
        default:
                *result = EINVAL;
                return -1;
        }
}

tfile mem_tfile (buffer, length)
        char *buffer;
        int length;
{
        register struct iovec *ts =
                (struct iovec *) malloc (2 * sizeof (struct iovec));
        ts[0].iov_base = buffer;
        ts[0].iov_len = length;
        ts[1].iov_len = 0;
        return tcreate (length, (char *) ts, 1, tmem);
}

tfile memv_tfile (vec)
        register struct iovec *vec;
{
        register int i, len;
        for (i=0, len = 0; vec[i].iov_len; i++)
                len += vec[i].iov_len;
                
        return tcreate (len, (char *) vec, 0, tmem);
}