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      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 }
    100