[PATCH] btrfs-progs: support free space tree in mkfs

* [PATCH] btrfs-progs: support free space tree in mkfs
@ 2020-09-02 18:50 Boris Burkov
  2020-09-02 19:09 ` Josef Bacik
  2020-09-02 20:44 ` David Sterba
  0 siblings, 2 replies; 6+ messages in thread
From: Boris Burkov @ 2020-09-02 18:50 UTC (permalink / raw)
  To: Chris Mason, Josef Bacik, David Sterba
  Cc: linux-btrfs, kernel-team, Boris Burkov

Add a runtime feature (-R) flag for the free space tree. A filesystem
that is mkfs'd with -R free-space-tree then mounted with no options has
the same contents as one mkfs'd without the option, then mounted with
'-o space_cache=v2'.

The only tricky thing is in exactly how to call the tree creation code.
Using btrfs_create_free_space_tree as is did not quite work, because an
extra reference to the eb (root->commit_root) is leaked, which mkfs
complains about with a warning. I opted to follow how the uuid tree is
created by adding it to the dirty roots list for cleanup by
commit_tree_roots in commit_transaction. As a result,
btrfs_create_free_space_tree no longer exactly matches the version in
the kernel sources.

Signed-off-by: Boris Burkov <boris@bur.io>
---
 common/fsfeatures.c             | 3 +++
 common/fsfeatures.h             | 3 ++-
 kernel-shared/disk-io.c         | 5 +++++
 kernel-shared/free-space-tree.c | 1 +
 mkfs/main.c                     | 8 ++++++++
 5 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/common/fsfeatures.c b/common/fsfeatures.c
index 48ab37ca..3bebc97f 100644
--- a/common/fsfeatures.c
+++ b/common/fsfeatures.c
@@ -107,6 +107,9 @@ static const struct btrfs_feature runtime_features[] = {
 	{ "quota", BTRFS_RUNTIME_FEATURE_QUOTA, NULL,
 		VERSION_TO_STRING2(3, 4), NULL, 0, NULL, 0,
 		"quota support (qgroups)" },
+	{ "free-space-tree", BTRFS_RUNTIME_FEATURE_FREE_SPACE_TREE, NULL,
+		VERSION_TO_STRING2(4, 5), NULL, 0, NULL, 0,
+		"free space tree (space_cache=v2)" },
 	/* Keep this one last */
 	{ "list-all", BTRFS_FEATURE_LIST_ALL, NULL }
 };
diff --git a/common/fsfeatures.h b/common/fsfeatures.h
index 13141254..f76fc099 100644
--- a/common/fsfeatures.h
+++ b/common/fsfeatures.h
@@ -39,7 +39,8 @@
 
 #define BTRFS_FEATURE_LIST_ALL		(1ULL << 63)
 
-#define BTRFS_RUNTIME_FEATURE_QUOTA	(1ULL << 0)
+#define BTRFS_RUNTIME_FEATURE_QUOTA		(1ULL << 0)
+#define BTRFS_RUNTIME_FEATURE_FREE_SPACE_TREE	(1ULL << 1)
 
 void btrfs_list_all_fs_features(u64 mask_disallowed);
 void btrfs_list_all_runtime_features(u64 mask_disallowed);
diff --git a/kernel-shared/disk-io.c b/kernel-shared/disk-io.c
index 42f733e3..6f584986 100644
--- a/kernel-shared/disk-io.c
+++ b/kernel-shared/disk-io.c
@@ -1003,10 +1003,15 @@ int btrfs_setup_all_roots(struct btrfs_fs_info *fs_info, u64 root_tree_bytenr,
 		ret = find_and_setup_root(root, fs_info, BTRFS_FREE_SPACE_TREE_OBJECTID,
 					  fs_info->free_space_root);
 		if (ret) {
+			free(fs_info->free_space_root);
+			fs_info->free_space_root = NULL;
 			printk("Couldn't read free space tree\n");
 			return -EIO;
 		}
 		fs_info->free_space_root->track_dirty = 1;
+	} else {
+		free(fs_info->free_space_root);
+		fs_info->free_space_root = NULL;
 	}
 
 	ret = find_and_setup_log_root(root, fs_info, sb);
diff --git a/kernel-shared/free-space-tree.c b/kernel-shared/free-space-tree.c
index 3570a9ac..2edc7fc7 100644
--- a/kernel-shared/free-space-tree.c
+++ b/kernel-shared/free-space-tree.c
@@ -1433,6 +1433,7 @@ int btrfs_create_free_space_tree(struct btrfs_fs_info *fs_info)
 		goto abort;
 	}
 	fs_info->free_space_root = free_space_root;
+	add_root_to_dirty_list(free_space_root);
 
 	do {
 		block_group = btrfs_lookup_first_block_group(fs_info, start);
diff --git a/mkfs/main.c b/mkfs/main.c
index 18dc6f8e..3eb74821 100644
--- a/mkfs/main.c
+++ b/mkfs/main.c
@@ -34,6 +34,7 @@
 #include <blkid/blkid.h>
 #include "kernel-shared/ctree.h"
 #include "kernel-shared/disk-io.h"
+#include "kernel-shared/free-space-tree.h"
 #include "kernel-shared/volumes.h"
 #include "kernel-shared/transaction.h"
 #include "common/utils.h"
@@ -1495,6 +1496,13 @@ raid_groups:
 			goto out;
 		}
 	}
+	if (runtime_features & BTRFS_RUNTIME_FEATURE_FREE_SPACE_TREE) {
+		ret = btrfs_create_free_space_tree(fs_info);
+		if (ret < 0) {
+			error("failed to create free space tree: %d (%m)", ret);
+			goto out;
+		}
+	}
 	if (verbose) {
 		char features_buf[64];
 
-- 
2.24.1


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