utilize st_blksize field to optimize size of reads and writes

[unix-history] / usr / src / lib / libc / stdio / filbuf.c

/* @(#)filbuf.c 4.4 (Berkeley) %G% */
#include        <stdio.h>
#include        <sys/types.h>
#include        <sys/stat.h>
char    *malloc();

_filbuf(iop)
register FILE *iop;
{
       int size;
       struct stat stbuf;
       static char smallbuf[_NFILE];
       extern char _sibuf[];

       if (iop->_flag & _IORW)
               iop->_flag |= _IOREAD;

       if ((iop->_flag&_IOREAD) == 0)
               return(EOF);
       if (iop->_flag&_IOSTRG)
               return(EOF);
tryagain:
       if (iop->_base==NULL) {
               if (iop->_flag&_IONBF) {
                       iop->_base = &smallbuf[fileno(iop)];
                       goto tryagain;
               }
               if (fstat(fileno(iop), &stbuf) < 0 || stbuf.st_blksize <= NULL)
                       size = BUFSIZ;
               else
                       size = stbuf.st_blksize;
               if (iop == stdin)
                       iop->_base = _sibuf;
               else {
                       if ((iop->_base = malloc(size)) == NULL) {
                               iop->_flag |= _IONBF;
                               goto tryagain;
                       }
                       iop->_flag |= _IOMYBUF;
               }
               iop->_bufsiz = size;
       }
       if (iop == stdin && (stdout->_flag&_IOLBF))
               fflush(stdout);
       iop->_cnt = read(fileno(iop), iop->_base,
               iop->_flag & _IONBF ? 1 : iop->_bufsiz);
       iop->_ptr = iop->_base;
       if (--iop->_cnt < 0) {
               if (iop->_cnt == -1) {
                       iop->_flag |= _IOEOF;
                       if (iop->_flag & _IORW)
                               iop->_flag &= ~_IOREAD;
               } else
                       iop->_flag |= _IOERR;
               iop->_cnt = 0;
               return(-1);
       }
       return(*iop->_ptr++&0377);
}