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 3 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, see <http://www.gnu.org/licenses/>.
  16  */
  17
  18 #include "includes.h"
  19
  20 /* Cache priming module.
  21  *
  22  * The purpose of this module is to do RAID stripe width reads to prime the
  23  * buffer cache to do zero-copy I/O for subsequent sendfile calls. The idea is
  24  * to do a single large read at the start of the file to make sure that most or
  25  * all of the file is pulled into the buffer cache. Subsequent I/Os have
  26  * reduced latency.
  27  *
  28  * Tunables.
  29  *
  30  *      cacheprime:rsize    Amount of readahead in bytes. This should be a
  31  *                          multiple of the RAID stripe width.
  32  *      cacheprime:debug    Debug level at which to emit messages.
  33  */
  34
  35 #define READAHEAD_MIN       (128 * 1024)        /* min is 128 KiB */
  36 #define READAHEAD_MAX       (100 * 1024 * 1024) /* max is 100 MiB */
  37
  38 #define MODULE "cacheprime"
  39
  40 static int module_debug;
  41 static ssize_t g_readsz = 0;
  42 static void * g_readbuf = NULL;
  43
  44 /* Prime the kernel buffer cache with data from the specified file. We use
  45  * per-fsp data to make sure we only ever do this once. If pread is being
  46  * emulated by seek/read/seek, when this will suck quite a lot.
  47  */
  48 static BOOL prime_cache(
  49             struct vfs_handle_struct *  handle,
  50                         files_struct *                  fsp,
  51                         int                                     fd,
  52                         SMB_OFF_T                           offset,
  53                         size_t                              count)
  54 {
  55         SMB_OFF_T * last;
  56         ssize_t nread;
  57
  58         last = VFS_ADD_FSP_EXTENSION(handle, fsp, SMB_OFF_T);
  59         if (!last) {
  60                 return False;
  61         }
  62
  63         if (*last == -1) {
  64             /* Readahead disabled. */
  65             return False;
  66         }
  67
  68         if ((*last + g_readsz) > (offset + count)) {
  69             /* Skip readahead ... we've already been here. */
  70             return False;
  71         }
  72
  73         DEBUG(module_debug,
  74             ("%s: doing readahead of %lld bytes at %lld for %s\n",
  75             MODULE, (long long)g_readsz, (long long)*last,
  76             fsp->fsp_name));
  77
  78         nread = sys_pread(fd, g_readbuf, g_readsz, *last);
  79         if (nread < 0) {
  80             *last = -1;
  81             return False;
  82         }
  83
  84         *last += nread;
  85         return True;
  86 }
  87
  88 static int cprime_connect(
  89                 struct vfs_handle_struct *  handle,
  90                 const char *                service,
  91                 const char *                user)
  92 {
  93         module_debug = lp_parm_int(SNUM(handle->conn), MODULE, "debug", 100);
  94         if (g_readbuf) {
  95                 /* Only allocate g_readbuf once. If the config changes and
  96                  * another client multiplexes onto this smbd, we don't want
  97                  * to risk memory corruption.
  98                  */
  99                 return SMB_VFS_NEXT_CONNECT(handle, service, user);
 100         }
 101
 102         g_readsz = conv_str_size(lp_parm_const_string(SNUM(handle->conn),
 103                                         MODULE, "rsize", NULL));
 104
 105         if (g_readsz < READAHEAD_MIN) {
 106                 DEBUG(module_debug, ("%s: %ld bytes of readahead "
 107                             "requested, using minimum of %u\n",
 108                             MODULE, (long)g_readsz, READAHEAD_MIN));
 109                 g_readsz = READAHEAD_MIN;
 110         } else if (g_readsz > READAHEAD_MAX) {
 111                 DEBUG(module_debug, ("%s: %ld bytes of readahead "
 112                             "requested, using maximum of %u\n",
 113                             MODULE, (long)g_readsz, READAHEAD_MAX));
 114                 g_readsz = READAHEAD_MAX;
 115         }
 116
 117         if ((g_readbuf = SMB_MALLOC(g_readsz)) == NULL) {
 118                 /* Turn off readahead if we can't get a buffer. */
 119                 g_readsz = 0;
 120         }
 121
 122         return SMB_VFS_NEXT_CONNECT(handle, service, user);
 123 }
 124
 125 static ssize_t cprime_sendfile(
 126                 struct vfs_handle_struct *  handle,
 127                 int                         tofd,
 128                 files_struct *              fsp,
 129                 int                         fromfd,
 130                 const DATA_BLOB *           header,
 131                 SMB_OFF_T                   offset,
 132                 size_t                      count)
 133 {
 134         if (g_readbuf && offset == 0) {
 135                 prime_cache(handle, fsp, fromfd, offset, count);
 136         }
 137
 138         return SMB_VFS_NEXT_SENDFILE(handle, tofd, fsp, fromfd,
 139                                      header, offset, count);
 140 }
 141
 142 static ssize_t cprime_read(
 143                 vfs_handle_struct * handle,
 144                 files_struct *      fsp,
 145                 int                 fd,
 146                 void *              data,
 147                 size_t              count)
 148 {
 149         SMB_OFF_T offset;
 150
 151         offset = SMB_VFS_LSEEK(fsp, fd, 0, SEEK_CUR);
 152         if (offset >= 0 && g_readbuf)  {
 153                 prime_cache(handle, fsp, fd, offset, count);
 154                 SMB_VFS_LSEEK(fsp, fd, offset, SEEK_SET);
 155         }
 156
 157         return SMB_VFS_NEXT_READ(handle, fsp, fd, data, count);
 158 }
 159
 160 static ssize_t cprime_pread(
 161                 vfs_handle_struct * handle,
 162                 files_struct *      fsp,
 163                 int                 fd,
 164                 void *              data,
 165                         size_t              count,
 166                 SMB_OFF_T           offset)
 167 {
 168         if (g_readbuf) {
 169                 prime_cache(handle, fsp, fd, offset, count);
 170         }
 171
 172         return SMB_VFS_NEXT_PREAD(handle, fsp, fd, data, count, offset);
 173 }
 174
 175 static vfs_op_tuple cprime_ops [] =
 176 {
 177         {SMB_VFS_OP(cprime_sendfile),
 178                 SMB_VFS_OP_SENDFILE, SMB_VFS_LAYER_TRANSPARENT},
 179         {SMB_VFS_OP(cprime_pread),
 180                 SMB_VFS_OP_PREAD, SMB_VFS_LAYER_TRANSPARENT},
 181         {SMB_VFS_OP(cprime_read),
 182                 SMB_VFS_OP_READ, SMB_VFS_LAYER_TRANSPARENT},
 183         {SMB_VFS_OP(cprime_connect),
 184                 SMB_VFS_OP_CONNECT,  SMB_VFS_LAYER_TRANSPARENT},
 185
 186         {SMB_VFS_OP(NULL), SMB_VFS_OP_NOOP, SMB_VFS_LAYER_NOOP}
 187 };
 188
 189 /* -------------------------------------------------------------------------
 190  * Samba module initialisation entry point.
 191  * -------------------------------------------------------------------------
 192  */
 193
 194 NTSTATUS vfs_cacheprime_init(void);
 195 NTSTATUS vfs_cacheprime_init(void)
 196 {
 197     return smb_register_vfs(SMB_VFS_INTERFACE_VERSION, MODULE, cprime_ops);
 198 }
 199
 200 /* vim: set sw=4 ts=4 tw=79 et: */