com32/lib/sys/fileread.c

   1 /* ----------------------------------------------------------------------- *
   2  *
   3  *   Copyright 2004-2008 H. Peter Anvin - All Rights Reserved
   4  *
   5  *   Permission is hereby granted, free of charge, to any person
   6  *   obtaining a copy of this software and associated documentation
   7  *   files (the "Software"), to deal in the Software without
   8  *   restriction, including without limitation the rights to use,
   9  *   copy, modify, merge, publish, distribute, sublicense, and/or
  10  *   sell copies of the Software, and to permit persons to whom
  11  *   the Software is furnished to do so, subject to the following
  12  *   conditions:
  13  *
  14  *   The above copyright notice and this permission notice shall
  15  *   be included in all copies or substantial portions of the Software.
  16  *
  17  *   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  18  *   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
  19  *   OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  20  *   NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
  21  *   HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
  22  *   WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  23  *   FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
  24  *   OTHER DEALINGS IN THE SOFTWARE.
  25  *
  26  * ----------------------------------------------------------------------- */
  27
  28 /*
  29  * read.c
  30  *
  31  * Reading from a file
  32  */
  33
  34 #include <errno.h>
  35 #include <string.h>
  36 #include <com32.h>
  37 #include <pmapi.h>
  38 #include <syslinux/pmapi.h>
  39 #include <minmax.h>
  40 #include "file.h"
  41
  42 int __file_get_block(struct file_info *fp)
  43 {
  44     ssize_t bytes_read;
  45
  46     bytes_read = pmapi_read_file(&fp->i.fd.handle, fp->i.buf,
  47                                           MAXBLOCK >> fp->i.fd.blocklg2);
  48     if (!bytes_read) {
  49         errno = EIO;
  50         return -1;
  51     }
  52
  53     fp->i.nbytes = bytes_read;
  54     fp->i.datap  = fp->i.buf;
  55     return 0;
  56 }
  57
  58 ssize_t __file_read(struct file_info * fp, void *buf, size_t count)
  59 {
  60     char *bufp = buf;
  61     ssize_t n = 0;
  62     size_t ncopy;
  63
  64     while (count) {
  65         if (fp->i.nbytes == 0) {
  66             if (fp->i.offset >= fp->i.fd.size || !fp->i.fd.handle)
  67                 return n;       /* As good as it gets... */
  68
  69             if (count > MAXBLOCK) {
  70                 /* Large transfer: copy directly, without buffering */
  71                 ncopy = pmapi_read_file(&fp->i.fd.handle, bufp,
  72                                                  count >> fp->i.fd.blocklg2);
  73                 if (!ncopy) {
  74                     errno = EIO;
  75                     return n ? n : -1;
  76                 }
  77
  78                 goto got_data;
  79             } else {
  80                 if (__file_get_block(fp))
  81                     return n ? n : -1;
  82             }
  83         }
  84
  85         ncopy = min(count, fp->i.nbytes);
  86         memcpy(bufp, fp->i.datap, ncopy);
  87
  88         fp->i.datap += ncopy;
  89         fp->i.offset += ncopy;
  90         fp->i.nbytes -= ncopy;
  91
  92     got_data:
  93         n += ncopy;
  94         bufp += ncopy;
  95         count -= ncopy;
  96     }
  97
  98     return n;
  99 }