source/modules/vfs_cacheprime.c

   1 /*
   2  * Copyright (c) James Peach 2005-2006
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; either version 2 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  17  */
  18
  19 #include "includes.h"
  20
  21 /* Cache priming module.
  22  *
  23  * The purpose of this module is to do RAID stripe width reads to prime the
  24  * buffer cache to do zero-copy I/O for subsequent sendfile calls. The idea is
  25  * to do a single large read at the start of the file to make sure that most or
  26  * all of the file is pulled into the buffer cache. Subsequent I/Os have
  27  * reduced latency.
  28  *
  29  * Tunables.
  30  *
  31  *      cacheprime:rsize    Amount of readahead in bytes. This should be a
  32  *                          multiple of the RAID stripe width.
  33  *      cacheprime:debug    Debug level at which to emit messages.
  34  */
  35
  36 #define READAHEAD_MIN       (128 * 1024)        /* min is 128 KiB */
  37 #define READAHEAD_MAX       (100 * 1024 * 1024) /* max is 100 MiB */
  38
  39 #define MODULE "cacheprime"
  40
  41 static int module_debug;
  42 static ssize_t g_readsz = 0;
  43 static void * g_readbuf = NULL;
  44
  45 /* Prime the kernel buffer cache with data from the specified file. We use
  46  * per-fsp data to make sure we only ever do this once. If pread is being
  47  * emulated by seek/read/seek, when this will suck quite a lot.
  48  */
  49 static BOOL prime_cache(
  50             struct vfs_handle_struct *  handle,
  51                         files_struct *                  fsp,
  52                         int                                     fd,
  53                         SMB_OFF_T                           offset,
  54                         size_t                              count)
  55 {
  56         SMB_OFF_T * last;
  57         ssize_t nread;
  58
  59         last = VFS_ADD_FSP_EXTENSION(handle, fsp, SMB_OFF_T);
  60         if (!last) {
  61                 return False;
  62         }
  63
  64         if (*last == -1) {
  65             /* Readahead disabled. */
  66             return False;
  67         }
  68
  69         if ((*last + g_readsz) > (offset + count)) {
  70             /* Skip readahead ... we've already been here. */
  71             return False;
  72         }
  73
  74         DEBUG(module_debug,
  75             ("%s: doing readahead of %lld bytes at %lld for %s\n",
  76             MODULE, (long long)g_readsz, (long long)*last,
  77             fsp->fsp_name));
  78
  79         nread = sys_pread(fd, g_readbuf, g_readsz, *last);
  80         if (nread < 0) {
  81             *last = -1;
  82             return False;
  83         }
  84
  85         *last += nread;
  86         return True;
  87 }
  88
  89 static int cprime_connect(
  90                 struct vfs_handle_struct *  handle,
  91                 const char *                service,
  92                 const char *                user)
  93 {
  94         module_debug = lp_parm_int(SNUM(handle->conn), MODULE, "debug", 100);
  95         if (g_readbuf) {
  96                 /* Only allocate g_readbuf once. If the config changes and
  97                  * another client multiplexes onto this smbd, we don't want
  98                  * to risk memory corruption.
  99                  */
 100                 return SMB_VFS_NEXT_CONNECT(handle, service, user);
 101         }
 102
 103         g_readsz = conv_str_size(lp_parm_const_string(SNUM(handle->conn),
 104                                         MODULE, "rsize", NULL));
 105
 106         if (g_readsz < READAHEAD_MIN) {
 107                 DEBUG(module_debug, ("%s: %ld bytes of readahead "
 108                             "requested, using minimum of %u\n",
 109                             MODULE, (long)g_readsz, READAHEAD_MIN));
 110                 g_readsz = READAHEAD_MIN;
 111         } else if (g_readsz > READAHEAD_MAX) {
 112                 DEBUG(module_debug, ("%s: %ld bytes of readahead "
 113                             "requested, using maximum of %u\n",
 114                             MODULE, (long)g_readsz, READAHEAD_MAX));
 115                 g_readsz = READAHEAD_MAX;
 116         }
 117
 118         if ((g_readbuf = SMB_MALLOC(g_readsz)) == NULL) {
 119                 /* Turn off readahead if we can't get a buffer. */
 120                 g_readsz = 0;
 121         }
 122
 123         return SMB_VFS_NEXT_CONNECT(handle, service, user);
 124 }
 125
 126 static ssize_t cprime_sendfile(
 127                 struct vfs_handle_struct *  handle,
 128                 int                         tofd,
 129                 files_struct *              fsp,
 130                 int                         fromfd,
 131                 const DATA_BLOB *           header,
 132                 SMB_OFF_T                   offset,
 133                 size_t                      count)
 134 {
 135         if (g_readbuf && offset == 0) {
 136                 prime_cache(handle, fsp, fromfd, offset, count);
 137         }
 138
 139         return SMB_VFS_NEXT_SENDFILE(handle, tofd, fsp, fromfd,
 140                                      header, offset, count);
 141 }
 142
 143 static ssize_t cprime_read(
 144                 vfs_handle_struct * handle,
 145                 files_struct *      fsp,
 146                 int                 fd,
 147                 void *              data,
 148                 size_t              count)
 149 {
 150         SMB_OFF_T offset;
 151
 152         offset = SMB_VFS_LSEEK(fsp, fd, 0, SEEK_CUR);
 153         if (offset >= 0 && g_readbuf)  {
 154                 prime_cache(handle, fsp, fd, offset, count);
 155                 SMB_VFS_LSEEK(fsp, fd, offset, SEEK_SET);
 156         }
 157
 158         return SMB_VFS_NEXT_READ(handle, fsp, fd, data, count);
 159 }
 160
 161 static ssize_t cprime_pread(
 162                 vfs_handle_struct * handle,
 163                 files_struct *      fsp,
 164                 int                 fd,
 165                 void *              data,
 166                         size_t              count,
 167                 SMB_OFF_T           offset)
 168 {
 169         if (g_readbuf) {
 170                 prime_cache(handle, fsp, fd, offset, count);
 171         }
 172
 173         return SMB_VFS_NEXT_PREAD(handle, fsp, fd, data, count, offset);
 174 }
 175
 176 static vfs_op_tuple cprime_ops [] =
 177 {
 178         {SMB_VFS_OP(cprime_sendfile),
 179                 SMB_VFS_OP_SENDFILE, SMB_VFS_LAYER_TRANSPARENT},
 180         {SMB_VFS_OP(cprime_pread),
 181                 SMB_VFS_OP_PREAD, SMB_VFS_LAYER_TRANSPARENT},
 182         {SMB_VFS_OP(cprime_read),
 183                 SMB_VFS_OP_READ, SMB_VFS_LAYER_TRANSPARENT},
 184         {SMB_VFS_OP(cprime_connect),
 185                 SMB_VFS_OP_CONNECT,  SMB_VFS_LAYER_TRANSPARENT},
 186
 187         {SMB_VFS_OP(NULL), SMB_VFS_OP_NOOP, SMB_VFS_LAYER_NOOP}
 188 };
 189
 190 /* -------------------------------------------------------------------------
 191  * Samba module initialisation entry point.
 192  * -------------------------------------------------------------------------
 193  */
 194
 195 NTSTATUS vfs_cacheprime_init(void);
 196 NTSTATUS vfs_cacheprime_init(void)
 197 {
 198     return smb_register_vfs(SMB_VFS_INTERFACE_VERSION, MODULE, cprime_ops);
 199 }
 200
 201 /* vim: set sw=4 ts=4 tw=79 et: */