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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
* the Free Software Foundation; either version 3 of the License, or
* (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
* along with this program; if not, see <http://www.gnu.org/licenses/>.
*/
#include "includes.h"
#include "smbd/smbd.h"
#include "lib/util/sys_rw.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.
*/
static bool prime_cache(
struct vfs_handle_struct * handle,
files_struct * fsp,
off_t offset,
size_t count)
{
off_t * last;
ssize_t nread;
last = (off_t *)VFS_ADD_FSP_EXTENSION(handle, fsp, off_t, NULL);
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,
fsp_str_dbg(fsp)));
nread = sys_pread(fsp->fh->fd, g_readbuf, g_readsz, *last);
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)
{
int ret;
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);
}
ret = SMB_VFS_NEXT_CONNECT(handle, service, user);
if (ret < 0) {
return ret;
}
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;
}
return 0;
}
static ssize_t cprime_sendfile(
struct vfs_handle_struct * handle,
int tofd,
files_struct * fromfsp,
const DATA_BLOB * header,
off_t offset,
size_t count)
{
if (g_readbuf && offset == 0) {
prime_cache(handle, fromfsp, offset, count);
}
return SMB_VFS_NEXT_SENDFILE(handle, tofd, fromfsp,
header, offset, count);
}
static ssize_t cprime_read(
vfs_handle_struct * handle,
files_struct * fsp,
void * data,
size_t count)
{
off_t offset;
offset = SMB_VFS_LSEEK(fsp, 0, SEEK_CUR);
if (offset >= 0 && g_readbuf) {
prime_cache(handle, fsp, offset, count);
SMB_VFS_LSEEK(fsp, offset, SEEK_SET);
}
return SMB_VFS_NEXT_READ(handle, fsp, data, count);
}
static ssize_t cprime_pread(
vfs_handle_struct * handle,
files_struct * fsp,
void * data,
size_t count,
off_t offset)
{
if (g_readbuf) {
prime_cache(handle, fsp, offset, count);
}
return SMB_VFS_NEXT_PREAD(handle, fsp, data, count, offset);
}
static struct vfs_fn_pointers vfs_cacheprime_fns = {
.sendfile_fn = cprime_sendfile,
.pread_fn = cprime_pread,
.read_fn = cprime_read,
.connect_fn = cprime_connect,
};
/* -------------------------------------------------------------------------
* Samba module initialisation entry point.
* -------------------------------------------------------------------------
*/
NTSTATUS vfs_cacheprime_init(void);
NTSTATUS vfs_cacheprime_init(void)
{
return smb_register_vfs(SMB_VFS_INTERFACE_VERSION, MODULE,
&vfs_cacheprime_fns);
}
/* vim: set sw=4 ts=4 tw=79 et: */
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