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 <syslinux/pmapi.h>
  38 #include <minmax.h>
  39 #include "file.h"
  40
  41 int __file_get_block(struct file_info *fp)
  42 {
  43     ssize_t bytes_read;
  44
  45     bytes_read = __com32.cs_pm->read_file(&fp->i.fd.handle, fp->i.buf,
  46                                           MAXBLOCK >> fp->i.fd.blocklg2);
  47     if (!bytes_read) {
  48         errno = EIO;
  49         return -1;
  50     }
  51
  52     fp->i.nbytes = bytes_read;
  53     fp->i.datap  = fp->i.buf;
  54     return 0;
  55 }
  56
  57 ssize_t __file_read(struct file_info * fp, void *buf, size_t count)
  58 {
  59     char *bufp = buf;
  60     ssize_t n = 0;
  61     size_t ncopy;
  62
  63     while (count) {
  64         if (fp->i.nbytes == 0) {
  65             if (fp->i.offset >= fp->i.fd.size || !fp->i.fd.handle)
  66                 return n;       /* As good as it gets... */
  67
  68             if (count > MAXBLOCK) {
  69                 /* Large transfer: copy directly, without buffering */
  70                 ncopy = __com32.cs_pm->read_file(&fp->i.fd.handle, bufp,
  71                                                  count >> fp->i.fd.blocklg2);
  72                 if (!ncopy) {
  73                     errno = EIO;
  74                     return n ? n : -1;
  75                 }
  76
  77                 goto got_data;
  78             } else {
  79                 if (__file_get_block(fp))
  80                     return n ? n : -1;
  81             }
  82         }
  83
  84         ncopy = min(count, fp->i.nbytes);
  85         memcpy(bufp, fp->i.datap, ncopy);
  86
  87         fp->i.datap += ncopy;
  88         fp->i.offset += ncopy;
  89         fp->i.nbytes -= ncopy;
  90
  91     got_data:
  92         n += ncopy;
  93         bufp += ncopy;
  94         count -= ncopy;
  95     }
  96
  97     return n;
  98 }