btrfs: move ulists to data extent sharedness check context

When calling btrfs_is_data_extent_shared() we pass two ulists that were
allocated by the caller. This is because the single caller, fiemap, calls
btrfs_is_data_extent_shared() multiple times and the ulists can be reused,
instead of allocating new ones before each call and freeing them after
each call.

Now that we have a context structure/object that we pass to
btrfs_is_data_extent_shared(), we can move those ulists to it, and hide
their allocation and the context's allocation in a helper function, as
well as the freeing of the ulists and the context object. This allows to
reduce the number of parameters passed to btrfs_is_data_extent_shared(),
the need to pass the ulists from extent_fiemap() to fiemap_process_hole()
and having the caller deal with allocating and releasing the ulists.

Also rename one of the ulists from 'tmp' / 'tmp_ulist' to 'refs', since
that's a much better name as it reflects what the list is used for (and
matching the argument name for find_parent_nodes()).
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/backref.c

@@ -1655,6 +1655,30 @@ static void store_backref_shared_cache(struct btrfs_backref_share_check_ctx *ctx
 	}
 }
 
+struct btrfs_backref_share_check_ctx *btrfs_alloc_backref_share_check_ctx(void)
+{
+	struct btrfs_backref_share_check_ctx *ctx;
+
+	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+	if (!ctx)
+		return NULL;
+
+	ulist_init(&ctx->refs);
+	ulist_init(&ctx->roots);
+
+	return ctx;
+}
+
+void btrfs_free_backref_share_ctx(struct btrfs_backref_share_check_ctx *ctx)
+{
+	if (!ctx)
+		return;
+
+	ulist_release(&ctx->refs);
+	ulist_release(&ctx->roots);
+	kfree(ctx);
+}
+
 /*
  * Check if a data extent is shared or not.
  *
@@ -1662,8 +1686,6 @@ static void store_backref_shared_cache(struct btrfs_backref_share_check_ctx *ctx
  * @bytenr:      Logical bytenr of the extent we are checking.
  * @extent_gen:  Generation of the extent (file extent item) or 0 if it is
  *               not known.
- * @roots:       List of roots this extent is shared among.
- * @tmp:         Temporary list used for iteration.
  * @ctx:         A backref sharedness check context.
  *
  * btrfs_is_data_extent_shared uses the backref walking code but will short
@@ -1679,7 +1701,6 @@ static void store_backref_shared_cache(struct btrfs_backref_share_check_ctx *ctx
  */
 int btrfs_is_data_extent_shared(struct btrfs_inode *inode, u64 bytenr,
 				u64 extent_gen,
-				struct ulist *roots, struct ulist *tmp,
 				struct btrfs_backref_share_check_ctx *ctx)
 {
 	struct btrfs_root *root = inode->root;
@@ -1697,8 +1718,8 @@ int btrfs_is_data_extent_shared(struct btrfs_inode *inode, u64 bytenr,
 	};
 	int level;
 
-	ulist_init(roots);
-	ulist_init(tmp);
+	ulist_init(&ctx->roots);
+	ulist_init(&ctx->refs);
 
 	trans = btrfs_join_transaction_nostart(root);
 	if (IS_ERR(trans)) {
@@ -1720,8 +1741,8 @@ int btrfs_is_data_extent_shared(struct btrfs_inode *inode, u64 bytenr,
 		bool is_shared;
 		bool cached;
 
-		ret = find_parent_nodes(trans, fs_info, bytenr, elem.seq, tmp,
-					roots, NULL, &shared, false);
+		ret = find_parent_nodes(trans, fs_info, bytenr, elem.seq, &ctx->refs,
+					&ctx->roots, NULL, &shared, false);
 		if (ret == BACKREF_FOUND_SHARED) {
 			/* this is the only condition under which we return 1 */
 			ret = 1;
@@ -1760,13 +1781,13 @@ int btrfs_is_data_extent_shared(struct btrfs_inode *inode, u64 bytenr,
 		 * deal with), we can not use it if we have multiple leaves
 		 * (which implies multiple paths).
 		 */
-		if (level == -1 && tmp->nnodes > 1)
+		if (level == -1 && ctx->refs.nnodes > 1)
 			ctx->use_path_cache = false;
 
 		if (level >= 0)
 			store_backref_shared_cache(ctx, root, bytenr,
 						   level, false);
-		node = ulist_next(tmp, &uiter);
+		node = ulist_next(&ctx->refs, &uiter);
 		if (!node)
 			break;
 		bytenr = node->val;
@@ -1789,8 +1810,8 @@ int btrfs_is_data_extent_shared(struct btrfs_inode *inode, u64 bytenr,
 		up_read(&fs_info->commit_root_sem);
 	}
 out:
-	ulist_release(roots);
-	ulist_release(tmp);
+	ulist_release(&ctx->roots);
+	ulist_release(&ctx->refs);
 	return ret;
 }
 

fs/btrfs/backref.h

@@ -24,6 +24,9 @@ struct btrfs_backref_shared_cache_entry {
 };
 
 struct btrfs_backref_share_check_ctx {
+	/* Ulists used during backref walking. */
+	struct ulist refs;
+	struct ulist roots;
 	/*
 	 * A path from a root to a leaf that has a file extent item pointing to
 	 * a given data extent should never exceed the maximum b+tree height.
@@ -35,6 +38,9 @@ struct btrfs_backref_share_check_ctx {
 typedef int (iterate_extent_inodes_t)(u64 inum, u64 offset, u64 root,
 		void *ctx);
 
+struct btrfs_backref_share_check_ctx *btrfs_alloc_backref_share_check_ctx(void);
+void btrfs_free_backref_share_ctx(struct btrfs_backref_share_check_ctx *ctx);
+
 int extent_from_logical(struct btrfs_fs_info *fs_info, u64 logical,
 			struct btrfs_path *path, struct btrfs_key *found_key,
 			u64 *flags);
@@ -79,7 +85,6 @@ int btrfs_find_one_extref(struct btrfs_root *root, u64 inode_objectid,
 			  u64 *found_off);
 int btrfs_is_data_extent_shared(struct btrfs_inode *inode, u64 bytenr,
 				u64 extent_gen,
-				struct ulist *roots, struct ulist *tmp,
 				struct btrfs_backref_share_check_ctx *ctx);
 
 int __init btrfs_prelim_ref_init(void);

fs/btrfs/extent_io.c

@@ -3708,7 +3708,6 @@ static int fiemap_process_hole(struct btrfs_inode *inode,
 			       struct btrfs_backref_share_check_ctx *backref_ctx,
 			       u64 disk_bytenr, u64 extent_offset,
 			       u64 extent_gen,
-			       struct ulist *roots, struct ulist *tmp_ulist,
 			       u64 start, u64 end)
 {
 	const u64 i_size = i_size_read(&inode->vfs_inode);
@@ -3752,10 +3751,9 @@ static int fiemap_process_hole(struct btrfs_inode *inode,
 		if (prealloc_len > 0) {
 			if (!checked_extent_shared && fieinfo->fi_extents_max) {
 				ret = btrfs_is_data_extent_shared(inode,
-							  disk_bytenr,
-							  extent_gen, roots,
-							  tmp_ulist,
-							  backref_ctx);
+								  disk_bytenr,
+								  extent_gen,
+								  backref_ctx);
 				if (ret < 0)
 					return ret;
 				else if (ret > 0)
@@ -3803,8 +3801,7 @@ static int fiemap_process_hole(struct btrfs_inode *inode,
 		if (!checked_extent_shared && fieinfo->fi_extents_max) {
 			ret = btrfs_is_data_extent_shared(inode,
 							  disk_bytenr,
-							  extent_gen, roots,
-							  tmp_ulist,
+							  extent_gen,
 							  backref_ctx);
 			if (ret < 0)
 				return ret;
@@ -3905,8 +3902,6 @@ int extent_fiemap(struct btrfs_inode *inode, struct fiemap_extent_info *fieinfo,
 	struct btrfs_path *path;
 	struct fiemap_cache cache = { 0 };
 	struct btrfs_backref_share_check_ctx *backref_ctx;
-	struct ulist *roots;
-	struct ulist *tmp_ulist;
 	u64 last_extent_end;
 	u64 prev_extent_end;
 	u64 lockstart;
@@ -3914,11 +3909,9 @@ int extent_fiemap(struct btrfs_inode *inode, struct fiemap_extent_info *fieinfo,
 	bool stopped = false;
 	int ret;
 
-	backref_ctx = kzalloc(sizeof(*backref_ctx), GFP_KERNEL);
+	backref_ctx = btrfs_alloc_backref_share_check_ctx();
 	path = btrfs_alloc_path();
-	roots = ulist_alloc(GFP_KERNEL);
-	tmp_ulist = ulist_alloc(GFP_KERNEL);
-	if (!backref_ctx || !path || !roots || !tmp_ulist) {
+	if (!backref_ctx || !path) {
 		ret = -ENOMEM;
 		goto out;
 	}
@@ -3979,7 +3972,6 @@ int extent_fiemap(struct btrfs_inode *inode, struct fiemap_extent_info *fieinfo,
 
 			ret = fiemap_process_hole(inode, fieinfo, &cache,
 						  backref_ctx, 0, 0, 0,
-						  roots, tmp_ulist,
 						  prev_extent_end, range_end);
 			if (ret < 0) {
 				goto out_unlock;
@@ -4021,13 +4013,12 @@ int extent_fiemap(struct btrfs_inode *inode, struct fiemap_extent_info *fieinfo,
 			ret = fiemap_process_hole(inode, fieinfo, &cache,
 						  backref_ctx,
 						  disk_bytenr, extent_offset,
-						  extent_gen, roots, tmp_ulist,
-						  key.offset, extent_end - 1);
+						  extent_gen, key.offset,
+						  extent_end - 1);
 		} else if (disk_bytenr == 0) {
 			/* We have an explicit hole. */
 			ret = fiemap_process_hole(inode, fieinfo, &cache,
 						  backref_ctx, 0, 0, 0,
-						  roots, tmp_ulist,
 						  key.offset, extent_end - 1);
 		} else {
 			/* We have a regular extent. */
@@ -4035,8 +4026,6 @@ int extent_fiemap(struct btrfs_inode *inode, struct fiemap_extent_info *fieinfo,
 				ret = btrfs_is_data_extent_shared(inode,
 								  disk_bytenr,
 								  extent_gen,
-								  roots,
-								  tmp_ulist,
 								  backref_ctx);
 				if (ret < 0)
 					goto out_unlock;
@@ -4087,8 +4076,7 @@ int extent_fiemap(struct btrfs_inode *inode, struct fiemap_extent_info *fieinfo,
 
 	if (!stopped && prev_extent_end < lockend) {
 		ret = fiemap_process_hole(inode, fieinfo, &cache, backref_ctx,
-					  0, 0, 0, roots, tmp_ulist,
-					  prev_extent_end, lockend - 1);
+					  0, 0, 0, prev_extent_end, lockend - 1);
 		if (ret < 0)
 			goto out_unlock;
 		prev_extent_end = lockend;
@@ -4119,10 +4107,8 @@ int extent_fiemap(struct btrfs_inode *inode, struct fiemap_extent_info *fieinfo,
 out_unlock:
 	unlock_extent(&inode->io_tree, lockstart, lockend, &cached_state);
 out:
-	kfree(backref_ctx);
+	btrfs_free_backref_share_ctx(backref_ctx);
 	btrfs_free_path(path);
-	ulist_free(roots);
-	ulist_free(tmp_ulist);
 	return ret;
 }