From: Bjorn Stenberg <bjorn@haxx.se>
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
This simple patch makes the linux fat filesystem driver use the
next_cluster field in the fat_boot_fsinfo structure. This field is a hint
where to start looking for free clusters.
Using this field makes a big difference for disks connected over slow links
such as USB 1.1. Finding the first free cluster on a 40gig fat-formatted
usb disk can today take several minutes. This patch cuts it down to a
fraction of a second.
Also, commit the next_cluster search hint toand from the superblock in
write_super/fill_super.
25-akpm/fs/fat/inode.c | 1 +
25-akpm/fs/fat/misc.c | 17 +++++++++++------
25-akpm/include/linux/msdos_fs.h | 3 +--
3 files changed, 13 insertions(+), 8 deletions(-)
diff -puN fs/fat/inode.c~fat-speedup fs/fat/inode.c
--- 25/fs/fat/inode.c~fat-speedup Wed Apr 23 14:11:03 2003
+++ 25-akpm/fs/fat/inode.c Wed Apr 23 14:11:03 2003
@@ -897,6 +897,7 @@ int fat_fill_super(struct super_block *s
sbi->fsinfo_sector);
} else {
sbi->free_clusters = CF_LE_L(fsinfo->free_clusters);
+ sbi->prev_free = CF_LE_L(fsinfo->next_cluster);
}
brelse(fsinfo_bh);
diff -puN fs/fat/misc.c~fat-speedup fs/fat/misc.c
--- 25/fs/fat/misc.c~fat-speedup Wed Apr 23 14:11:03 2003
+++ 25-akpm/fs/fat/misc.c Wed Apr 23 14:11:03 2003
@@ -74,6 +74,7 @@ void fat_clusters_flush(struct super_blo
MSDOS_SB(sb)->fsinfo_sector);
} else {
fsinfo->free_clusters = CF_LE_L(MSDOS_SB(sb)->free_clusters);
+ fsinfo->next_cluster = CF_LE_L(MSDOS_SB(sb)->prev_free);
mark_buffer_dirty(bh);
}
brelse(bh);
@@ -130,19 +131,23 @@ int fat_add_cluster(struct inode *inode)
unlock_fat(sb);
return -ENOSPC;
}
- limit = MSDOS_SB(sb)->clusters;
- for (count = 0; count < limit; count++) {
- nr = ((count + MSDOS_SB(sb)->prev_free) % limit) + 2;
+
+ limit = MSDOS_SB(sb)->clusters + 2;
+ nr = MSDOS_SB(sb)->prev_free + 1;
+ for (count = 0; count < MSDOS_SB(sb)->clusters; count++, nr++) {
+ nr = nr % limit;
+ if (nr < 2)
+ nr = 2;
if (fat_access(sb, nr, -1) == FAT_ENT_FREE)
break;
}
- if (count >= limit) {
+ if (count >= MSDOS_SB(sb)->clusters) {
MSDOS_SB(sb)->free_clusters = 0;
unlock_fat(sb);
return -ENOSPC;
}
-
- MSDOS_SB(sb)->prev_free = (count + MSDOS_SB(sb)->prev_free + 1) % limit;
+ MSDOS_SB(sb)->prev_free = nr;
+
fat_access(sb, nr, FAT_ENT_EOF);
if (MSDOS_SB(sb)->free_clusters != -1)
MSDOS_SB(sb)->free_clusters--;
diff -puN include/linux/msdos_fs.h~fat-speedup include/linux/msdos_fs.h
--- 25/include/linux/msdos_fs.h~fat-speedup Wed Apr 23 14:11:03 2003
+++ 25-akpm/include/linux/msdos_fs.h Wed Apr 23 14:11:03 2003
@@ -146,8 +146,7 @@ struct fat_boot_fsinfo {
__u32 reserved1[120]; /* Nothing as far as I can tell */
__u32 signature2; /* 0x61417272L */
__u32 free_clusters; /* Free cluster count. -1 if unknown */
- __u32 next_cluster; /* Most recently allocated cluster.
- * Unused under Linux. */
+ __u32 next_cluster; /* Most recently allocated cluster */
__u32 reserved2[4];
};
_