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/*
* orderfiles.c: order file accesses to optimise disk load
*
* Copyright (C) 2014 Colin Watson.
*
* Inspired by and loosely based on dpkg/src/filesdb.c, which is:
* Copyright (C) 1995 Ian Jackson <ian@chiark.greenend.org.uk>
* Copyright (C) 2000,2001 Wichert Akkerman <wakkerma@debian.org>
* Copyright (C) 2008-2014 Guillem Jover <guillem@debian.org>
*
* This file is part of man-db.
*
* man-db 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 2 of the License, or
* (at your option) any later version.
*
* man-db 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 man-db; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
#ifdef HAVE_CONFIG_H
# include "config.h"
#endif /* HAVE_CONFIG_H */
#ifdef HAVE_LINUX_FIEMAP_H
# include <linux/fiemap.h>
# include <linux/fs.h>
# include <sys/ioctl.h>
# include <sys/vfs.h>
#endif /* HAVE_LINUX_FIEMAP_H */
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "manconfig.h"
#include "hashtable.h"
struct hashtable *physical_offsets = NULL;
#if defined(HAVE_LINUX_FIEMAP_H)
int compare_physical_offsets (const void *a, const void *b)
{
const char *left = *(const char **) a;
const char *right = *(const char **) b;
uint64_t *left_offset_p = hashtable_lookup (physical_offsets,
left, strlen (left));
uint64_t *right_offset_p = hashtable_lookup (physical_offsets,
right, strlen (right));
uint64_t left_offset = left_offset_p ? *left_offset_p : UINT64_MAX;
uint64_t right_offset = right_offset_p ? *right_offset_p : UINT64_MAX;
if (left_offset < right_offset)
return -1;
else if (left_offset > right_offset)
return 1;
else
return 0;
}
void order_files (const char *dir, char **basenames, size_t n_basenames)
{
int dir_fd_open_flags;
int dir_fd;
struct statfs fs;
size_t i;
dir_fd_open_flags = O_SEARCH | O_DIRECTORY;
#ifdef O_PATH
dir_fd_open_flags |= O_PATH;
#endif
dir_fd = open (dir, dir_fd_open_flags);
if (dir_fd < 0)
return;
if (fstatfs (dir_fd, &fs) < 0) {
close (dir_fd);
return;
}
/* Sort files by the physical locations of their first blocks, in an
* attempt to minimise disk drive head movements. This assumes that
* files are small enough that they are likely to be in one block or
* a small number of contiguous blocks, which seems a reasonable
* assumption for manual pages.
*/
physical_offsets = hashtable_create (&free);
for (i = 0; i < n_basenames; ++i) {
struct {
struct fiemap fiemap;
struct fiemap_extent extent;
} fm;
int fd;
fd = openat (dir_fd, basenames[i], O_RDONLY);
if (fd < 0)
continue;
memset (&fm, 0, sizeof (fm));
fm.fiemap.fm_start = 0;
fm.fiemap.fm_length = fs.f_bsize;
fm.fiemap.fm_flags = 0;
fm.fiemap.fm_extent_count = 1;
if (ioctl (fd, FS_IOC_FIEMAP, (unsigned long) &fm) == 0) {
uint64_t *offset = XMALLOC (uint64_t);
*offset = fm.fiemap.fm_extents[0].fe_physical;
hashtable_install (physical_offsets, basenames[i],
strlen (basenames[i]), offset);
}
close (fd);
}
qsort (basenames, n_basenames, sizeof *basenames,
compare_physical_offsets);
hashtable_free (physical_offsets);
physical_offsets = NULL;
close (dir_fd);
}
#elif defined(HAVE_POSIX_FADVISE)
void order_files (const char *dir, char **basenames, size_t n_basenames)
{
int dir_fd_open_flags;
int dir_fd;
size_t i;
dir_fd_open_flags = O_SEARCH | O_DIRECTORY;
#ifdef O_PATH
dir_fd_open_flags |= O_PATH;
#endif
dir_fd = open (dir, dir_fd_open_flags);
if (dir_fd < 0)
return;
/* While we can't actually order the files, we can at least ask the
* kernel to preload them.
*/
for (i = 0; i < n_basenames; ++i) {
int fd = openat (dir_fd, basenames[i], O_RDONLY | O_NONBLOCK);
if (fd >= 0) {
posix_fadvise (fd, 0, 0, POSIX_FADV_WILLNEED);
close (fd);
}
}
close (dir_fd);
}
#else
void order_files (const char *dir, char **basenames, size_t n_basenames)
{
}
#endif
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