source/smbd/predict.c

   1 /*
   2    Unix SMB/Netbios implementation.
   3    Version 1.9.
   4    file read prediction routines
   5    Copyright (C) Andrew Tridgell 1992-1998
   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 #if USE_READ_PREDICTION
  27
  28 /* variables used by the read prediction module */
  29 static int rp_fd = -1;
  30 static SMB_OFF_T rp_offset = 0;
  31 static ssize_t rp_length = 0;
  32 static ssize_t rp_alloced = 0;
  33 static int rp_predict_fd = -1;
  34 static SMB_OFF_T rp_predict_offset = 0;
  35 static size_t rp_predict_length = 0;
  36 static int rp_timeout = 5;
  37 static time_t rp_time = 0;
  38 static char *rp_buffer = NULL;
  39 static BOOL predict_skip=False;
  40 extern time_t smb_last_time;
  41
  42 /****************************************************************************
  43 handle read prediction on a file
  44 ****************************************************************************/
  45 ssize_t read_predict(int fd,SMB_OFF_T offset,char *buf,char **ptr,size_t num)
  46 {
  47   ssize_t ret = 0;
  48   ssize_t possible = rp_length - (offset - rp_offset);
  49
  50   possible = MIN(possible,num);
  51
  52   /* give data if possible */
  53   if (fd == rp_fd &&
  54       offset >= rp_offset &&
  55       possible>0 &&
  56       smb_last_time-rp_time < rp_timeout)
  57   {
  58     ret = possible;
  59     if (buf)
  60       memcpy(buf,rp_buffer + (offset-rp_offset),possible);
  61     else
  62       *ptr = rp_buffer + (offset-rp_offset);
  63     DEBUG(5,("read-prediction gave %d bytes of %d\n",ret,num));
  64   }
  65
  66   if (ret == num) {
  67     predict_skip = True;
  68   } else {
  69     SMB_STRUCT_STAT rp_stat;
  70
  71     /* Find the end of the file - ensure we don't
  72        read predict beyond it. */
  73     if(sys_fstat(fd,&rp_stat) < 0)
  74     {
  75       DEBUG(0,("read-prediction failed on fstat. Error was %s\n", strerror(errno)));
  76       predict_skip = True;
  77     }
  78     else
  79     {
  80       predict_skip = False;
  81
  82       /* prepare the next prediction */
  83       rp_predict_fd = fd;
  84       /* Make sure we don't seek beyond the end of the file. */
  85       rp_predict_offset = MIN((offset + num),rp_stat.st_size);
  86       rp_predict_length = num;
  87     }
  88   }
  89
  90   if (ret < 0) ret = 0;
  91
  92   return(ret);
  93 }
  94
  95 /****************************************************************************
  96 pre-read some data
  97 ****************************************************************************/
  98 void do_read_prediction(void)
  99 {
 100   static size_t readsize = 0;
 101
 102   if (predict_skip) return;
 103
 104   if (rp_predict_fd == -1)
 105     return;
 106
 107   rp_fd = rp_predict_fd;
 108   rp_offset = rp_predict_offset;
 109   rp_length = 0;
 110
 111   rp_predict_fd = -1;
 112
 113   if (readsize == 0) {
 114     readsize = lp_readsize();
 115     readsize = MAX(readsize,1024);
 116   }
 117
 118   rp_predict_length = MIN(rp_predict_length,2*readsize);
 119   rp_predict_length = MAX(rp_predict_length,1024);
 120   rp_offset = (rp_offset/1024)*1024;
 121   rp_predict_length = (rp_predict_length/1024)*1024;
 122
 123   if (rp_predict_length > rp_alloced)
 124     {
 125       rp_buffer = Realloc(rp_buffer,rp_predict_length);
 126       rp_alloced = rp_predict_length;
 127       if (!rp_buffer)
 128         {
 129           DEBUG(0,("can't allocate read-prediction buffer\n"));
 130           rp_predict_fd = -1;
 131           rp_fd = -1;
 132           rp_alloced = 0;
 133           return;
 134         }
 135     }
 136
 137   if (sys_lseek(rp_fd,rp_offset,SEEK_SET) != rp_offset) {
 138     rp_fd = -1;
 139     rp_predict_fd = -1;
 140     return;
 141   }
 142
 143   rp_length = read(rp_fd,rp_buffer,rp_predict_length);
 144   rp_time = time(NULL);
 145   if (rp_length < 0)
 146     rp_length = 0;
 147 }
 148
 149 /****************************************************************************
 150 invalidate read-prediction on a fd
 151 ****************************************************************************/
 152 void invalidate_read_prediction(int fd)
 153 {
 154  if (rp_fd == fd)
 155    rp_fd = -1;
 156  if (rp_predict_fd == fd)
 157    rp_predict_fd = -1;
 158 }
 159
 160 #else
 161  void read_prediction_dummy(void) ;
 162 #endif