[PATCH] Btrfs: introduce mount option no_space_cache

[Josef Bacik <josef@redhat.com>]

Some users have requested this and I've found I needed a way to disable cache
loading without actually clearing the cache, so introduce the no_space_cache
option.  Before we check the super blocks cache generation field and if it was
populated we always turned space caching on.  Now we check this and set the
space cache option on, and then parse the mount options so that if we want it
off it get's turned off.  Then we check the mount option all the places we do
the caching work instead of checking the super's cache generation.  This makes
things more consistent and lets us turn space caching off.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>
---
 fs/btrfs/extent-tree.c |    9 ++++-----
 fs/btrfs/super.c       |   23 ++++++++++++++++++-----
 fs/btrfs/transaction.c |    2 +-
 3 files changed, 23 insertions(+), 11 deletions(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 25b69d0..f9711a8 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -481,7 +481,8 @@ static int cache_block_group(struct btrfs_block_group_cache *cache,
 	 * we likely hold important locks.
 	 */
 	if (trans && (!trans->transaction->in_commit) &&
-	    (root && root != root->fs_info->tree_root)) {
+	    (root && root != root->fs_info->tree_root) &&
+	    btrfs_test_opt(root, SPACE_CACHE)) {
 		spin_lock(&cache->lock);
 		if (cache->cached != BTRFS_CACHE_NO) {
 			spin_unlock(&cache->lock);
@@ -4223,7 +4224,7 @@ static int update_block_group(struct btrfs_trans_handle *trans,
 		spin_lock(&cache->space_info->lock);
 		spin_lock(&cache->lock);
 
-		if (btrfs_super_cache_generation(&info->super_copy) != 0 &&
+		if (btrfs_test_opt(root, SPACE_CACHE) &&
 		    cache->disk_cache_state < BTRFS_DC_CLEAR)
 			cache->disk_cache_state = BTRFS_DC_CLEAR;
 
@@ -7038,13 +7039,11 @@ int btrfs_read_block_groups(struct btrfs_root *root)
 	path->reada = 1;
 
 	cache_gen = btrfs_super_cache_generation(&root->fs_info->super_copy);
-	if (cache_gen != 0 &&
+	if (btrfs_test_opt(root, SPACE_CACHE) &&
 	    btrfs_super_generation(&root->fs_info->super_copy) != cache_gen)
 		need_clear = 1;
 	if (btrfs_test_opt(root, CLEAR_CACHE))
 		need_clear = 1;
-	if (!btrfs_test_opt(root, SPACE_CACHE) && cache_gen)
-		printk(KERN_INFO "btrfs: disk space caching is enabled\n");
 
 	while (1) {
 		ret = find_first_block_group(root, path, &key);
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 934789f..bfee12d 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -164,7 +164,7 @@ enum {
 	Opt_notreelog, Opt_ratio, Opt_flushoncommit, Opt_discard,
 	Opt_space_cache, Opt_clear_cache, Opt_user_subvol_rm_allowed,
 	Opt_enospc_debug, Opt_subvolrootid, Opt_defrag,
-	Opt_inode_cache, Opt_err,
+	Opt_inode_cache, Opt_no_space_cache, Opt_err,
 };
 
 static match_table_t tokens = {
@@ -197,6 +197,7 @@ static match_table_t tokens = {
 	{Opt_subvolrootid, "subvolrootid=%d"},
 	{Opt_defrag, "autodefrag"},
 	{Opt_inode_cache, "inode_cache"},
+	{Opt_no_space_cache, "no_space_cache"},
 	{Opt_err, NULL},
 };
 
@@ -208,14 +209,19 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
 {
 	struct btrfs_fs_info *info = root->fs_info;
 	substring_t args[MAX_OPT_ARGS];
-	char *p, *num, *orig;
+	char *p, *num, *orig = NULL;
+	u64 cache_gen;
 	int intarg;
 	int ret = 0;
 	char *compress_type;
 	bool compress_force = false;
 
+	cache_gen = btrfs_super_cache_generation(&root->fs_info->super_copy);
+	if (cache_gen)
+		btrfs_set_opt(info->mount_opt, SPACE_CACHE);
+
 	if (!options)
-		return 0;
+		goto out;
 
 	/*
 	 * strsep changes the string, duplicate it because parse_options
@@ -362,9 +368,12 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
 			btrfs_set_opt(info->mount_opt, DISCARD);
 			break;
 		case Opt_space_cache:
-			printk(KERN_INFO "btrfs: enabling disk space caching\n");
 			btrfs_set_opt(info->mount_opt, SPACE_CACHE);
 			break;
+		case Opt_no_space_cache:
+			printk(KERN_INFO "btrfs: disabling disk space caching\n");
+			btrfs_clear_opt(info->mount_opt, SPACE_CACHE);
+			break;
 		case Opt_inode_cache:
 			printk(KERN_INFO "btrfs: enabling inode map caching\n");
 			btrfs_set_opt(info->mount_opt, INODE_MAP_CACHE);
@@ -393,6 +402,8 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
 		}
 	}
 out:
+	if (!ret && btrfs_test_opt(root, SPACE_CACHE))
+		printk(KERN_INFO "btrfs: disk space caching is enabled\n");
 	kfree(orig);
 	return ret;
 }
@@ -686,7 +697,9 @@ static int btrfs_show_options(struct seq_file *seq, struct vfsmount *vfs)
 	if (!(root->fs_info->sb->s_flags & MS_POSIXACL))
 		seq_puts(seq, ",noacl");
 	if (btrfs_test_opt(root, SPACE_CACHE))
-		seq_puts(seq, ",space_cache");
+		seq_puts(seq, ",space_cache=on");
+	else
+		seq_puts(seq, ",space_cache=off");
 	if (btrfs_test_opt(root, CLEAR_CACHE))
 		seq_puts(seq, ",clear_cache");
 	if (btrfs_test_opt(root, USER_SUBVOL_RM_ALLOWED))
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 4565579..1e1a481 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -1003,7 +1003,7 @@ static void update_super_roots(struct btrfs_root *root)
 	super->root = root_item->bytenr;
 	super->generation = root_item->generation;
 	super->root_level = root_item->level;
-	if (super->cache_generation != 0 || btrfs_test_opt(root, SPACE_CACHE))
+	if (btrfs_test_opt(root, SPACE_CACHE))
 		super->cache_generation = root_item->generation;
 }
 
-- 
1.7.5.2