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/*
* Copyright ( c ) James Peach 2005 - 2006
*
* This program is free software ; you can redistribute it and / or modify
* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation ; either version 3 of the License , or
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* ( at your option ) any later version .
*
* This program is distributed in the hope that it will be useful ,
* but WITHOUT ANY WARRANTY ; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE . See the
* GNU General Public License for more details .
*
* You should have received a copy of the GNU General Public License
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* along with this program ; if not , see < http : //www.gnu.org/licenses/>.
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*/
# include "includes.h"
/* Cache priming module.
*
* The purpose of this module is to do RAID stripe width reads to prime the
* buffer cache to do zero - copy I / O for subsequent sendfile calls . The idea is
* to do a single large read at the start of the file to make sure that most or
* all of the file is pulled into the buffer cache . Subsequent I / Os have
* reduced latency .
*
* Tunables .
*
* cacheprime : rsize Amount of readahead in bytes . This should be a
* multiple of the RAID stripe width .
* cacheprime : debug Debug level at which to emit messages .
*/
# define READAHEAD_MIN (128 * 1024) /* min is 128 KiB */
# define READAHEAD_MAX (100 * 1024 * 1024) /* max is 100 MiB */
# define MODULE "cacheprime"
static int module_debug ;
static ssize_t g_readsz = 0 ;
static void * g_readbuf = NULL ;
/* Prime the kernel buffer cache with data from the specified file. We use
* per - fsp data to make sure we only ever do this once . If pread is being
* emulated by seek / read / seek , when this will suck quite a lot .
*/
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static bool prime_cache (
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struct vfs_handle_struct * handle ,
files_struct * fsp ,
SMB_OFF_T offset ,
size_t count )
{
SMB_OFF_T * last ;
ssize_t nread ;
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last = ( SMB_OFF_T * ) VFS_ADD_FSP_EXTENSION ( handle , fsp , SMB_OFF_T , NULL ) ;
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if ( ! last ) {
return False ;
}
if ( * last = = - 1 ) {
/* Readahead disabled. */
return False ;
}
if ( ( * last + g_readsz ) > ( offset + count ) ) {
/* Skip readahead ... we've already been here. */
return False ;
}
DEBUG ( module_debug ,
( " %s: doing readahead of %lld bytes at %lld for %s \n " ,
MODULE , ( long long ) g_readsz , ( long long ) * last ,
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fsp_str_dbg ( fsp ) ) ) ;
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nread = sys_pread ( fsp - > fh - > fd , g_readbuf , g_readsz , * last ) ;
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if ( nread < 0 ) {
* last = - 1 ;
return False ;
}
* last + = nread ;
return True ;
}
static int cprime_connect (
struct vfs_handle_struct * handle ,
const char * service ,
const char * user )
{
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int ret ;
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module_debug = lp_parm_int ( SNUM ( handle - > conn ) , MODULE , " debug " , 100 ) ;
if ( g_readbuf ) {
/* Only allocate g_readbuf once. If the config changes and
* another client multiplexes onto this smbd , we don ' t want
* to risk memory corruption .
*/
return SMB_VFS_NEXT_CONNECT ( handle , service , user ) ;
}
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ret = SMB_VFS_NEXT_CONNECT ( handle , service , user ) ;
if ( ret < 0 ) {
return ret ;
}
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g_readsz = conv_str_size ( lp_parm_const_string ( SNUM ( handle - > conn ) ,
MODULE , " rsize " , NULL ) ) ;
if ( g_readsz < READAHEAD_MIN ) {
DEBUG ( module_debug , ( " %s: %ld bytes of readahead "
" requested, using minimum of %u \n " ,
MODULE , ( long ) g_readsz , READAHEAD_MIN ) ) ;
g_readsz = READAHEAD_MIN ;
} else if ( g_readsz > READAHEAD_MAX ) {
DEBUG ( module_debug , ( " %s: %ld bytes of readahead "
" requested, using maximum of %u \n " ,
MODULE , ( long ) g_readsz , READAHEAD_MAX ) ) ;
g_readsz = READAHEAD_MAX ;
}
if ( ( g_readbuf = SMB_MALLOC ( g_readsz ) ) = = NULL ) {
/* Turn off readahead if we can't get a buffer. */
g_readsz = 0 ;
}
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return 0 ;
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}
static ssize_t cprime_sendfile (
struct vfs_handle_struct * handle ,
int tofd ,
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files_struct * fromfsp ,
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const DATA_BLOB * header ,
SMB_OFF_T offset ,
size_t count )
{
if ( g_readbuf & & offset = = 0 ) {
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prime_cache ( handle , fromfsp , offset , count ) ;
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}
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return SMB_VFS_NEXT_SENDFILE ( handle , tofd , fromfsp ,
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header , offset , count ) ;
}
static ssize_t cprime_read (
vfs_handle_struct * handle ,
files_struct * fsp ,
void * data ,
size_t count )
{
SMB_OFF_T offset ;
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offset = SMB_VFS_LSEEK ( fsp , 0 , SEEK_CUR ) ;
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if ( offset > = 0 & & g_readbuf ) {
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prime_cache ( handle , fsp , offset , count ) ;
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SMB_VFS_LSEEK ( fsp , offset , SEEK_SET ) ;
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}
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return SMB_VFS_NEXT_READ ( handle , fsp , data , count ) ;
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}
static ssize_t cprime_pread (
vfs_handle_struct * handle ,
files_struct * fsp ,
void * data ,
size_t count ,
SMB_OFF_T offset )
{
if ( g_readbuf ) {
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prime_cache ( handle , fsp , offset , count ) ;
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}
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return SMB_VFS_NEXT_PREAD ( handle , fsp , data , count , offset ) ;
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}
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static struct vfs_fn_pointers vfs_cacheprime_fns = {
. sendfile = cprime_sendfile ,
. pread = cprime_pread ,
. vfs_read = cprime_read ,
. connect_fn = cprime_connect ,
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} ;
/* -------------------------------------------------------------------------
* Samba module initialisation entry point .
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
*/
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NTSTATUS vfs_cacheprime_init ( void ) ;
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NTSTATUS vfs_cacheprime_init ( void )
{
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return smb_register_vfs ( SMB_VFS_INTERFACE_VERSION , MODULE ,
& vfs_cacheprime_fns ) ;
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}
/* vim: set sw=4 ts=4 tw=79 et: */