source/smbd/predict.c

   1 /*
   2    Unix SMB/Netbios implementation.
   3    Version 1.9.
   4    file read prediction routines
   5    Copyright (C) Andrew Tridgell 1992-1997
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 2 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program; if not, write to the Free Software
  19    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  20 */
  21
  22 #include "includes.h"
  23
  24 extern int DEBUGLEVEL;
  25
  26
  27 /* variables used by the read prediction module */
  28 static int rp_fd = -1;
  29 static int rp_offset = 0;
  30 static int rp_length = 0;
  31 static int rp_alloced = 0;
  32 static int rp_predict_fd = -1;
  33 static int rp_predict_offset = 0;
  34 static int rp_predict_length = 0;
  35 static int rp_timeout = 5;
  36 static time_t rp_time = 0;
  37 static char *rp_buffer = NULL;
  38 static BOOL predict_skip=False;
  39 time_t smb_last_time=(time_t)0;
  40
  41 /****************************************************************************
  42 handle read prediction on a file
  43 ****************************************************************************/
  44 int read_predict(int fd,int offset,char *buf,char **ptr,int num)
  45 {
  46   int ret = 0;
  47   int possible = rp_length - (offset - rp_offset);
  48
  49   possible = MIN(possible,num);
  50
  51   /* give data if possible */
  52   if (fd == rp_fd &&
  53       offset >= rp_offset &&
  54       possible>0 &&
  55       smb_last_time-rp_time < rp_timeout)
  56     {
  57       ret = possible;
  58       if (buf)
  59         memcpy(buf,rp_buffer + (offset-rp_offset),possible);
  60       else
  61         *ptr = rp_buffer + (offset-rp_offset);
  62       DEBUG(5,("read-prediction gave %d bytes of %d\n",ret,num));
  63     }
  64
  65   if (ret == num) {
  66     predict_skip = True;
  67   } else {
  68     predict_skip = False;
  69
  70     /* prepare the next prediction */
  71     rp_predict_fd = fd;
  72     rp_predict_offset = offset + num;
  73     rp_predict_length = num;
  74   }
  75
  76   if (ret < 0) ret = 0;
  77
  78   return(ret);
  79 }
  80
  81 /****************************************************************************
  82 pre-read some data
  83 ****************************************************************************/
  84 void do_read_prediction()
  85 {
  86   static int readsize = 0;
  87
  88   if (predict_skip) return;
  89
  90   if (rp_predict_fd == -1)
  91     return;
  92
  93   rp_fd = rp_predict_fd;
  94   rp_offset = rp_predict_offset;
  95   rp_length = 0;
  96
  97   rp_predict_fd = -1;
  98
  99   if (readsize == 0) {
 100     readsize = lp_readsize();
 101     readsize = MAX(readsize,1024);
 102   }
 103
 104   rp_predict_length = MIN(rp_predict_length,2*readsize);
 105   rp_predict_length = MAX(rp_predict_length,1024);
 106   rp_offset = (rp_offset/1024)*1024;
 107   rp_predict_length = (rp_predict_length/1024)*1024;
 108
 109   if (rp_predict_length > rp_alloced)
 110     {
 111       rp_buffer = Realloc(rp_buffer,rp_predict_length);
 112       rp_alloced = rp_predict_length;
 113       if (!rp_buffer)
 114         {
 115           DEBUG(0,("can't allocate read-prediction buffer\n"));
 116           rp_predict_fd = -1;
 117           rp_fd = -1;
 118           rp_alloced = 0;
 119           return;
 120         }
 121     }
 122
 123   if (lseek(rp_fd,rp_offset,SEEK_SET) != rp_offset) {
 124     rp_fd = -1;
 125     rp_predict_fd = -1;
 126     return;
 127   }
 128
 129   rp_length = read(rp_fd,rp_buffer,rp_predict_length);
 130   rp_time = time(NULL);
 131   if (rp_length < 0)
 132     rp_length = 0;
 133 }
 134
 135 /****************************************************************************
 136 invalidate read-prediction on a fd
 137 ****************************************************************************/
 138 void invalidate_read_prediction(int fd)
 139 {
 140  if (rp_fd == fd)
 141    rp_fd = -1;
 142  if (rp_predict_fd == fd)
 143    rp_predict_fd = -1;
 144 }
 145