[PATCH 6/8] btrfs-progs: introduce the experimental compat RO flag, WRITE_INTENT_BITMAP

[Qu Wenruo <wqu@suse.com>]

This new compat RO flag will only be enabled through experimental
features.

Since this feature has no real code implementation yet, only the
following code changes are added:

- New super block check
  To ensure WRITE_INTENT_BITMAP is enabled along with
  EXTRA_SUPER_RESERVED

- New compat RO flag readable string output

- New mkfs runtime features

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 common/fsfeatures.c        | 11 +++++++++++
 common/fsfeatures.h        |  1 +
 kernel-shared/ctree.h      | 15 +++++++++++++++
 kernel-shared/disk-io.c    |  9 +++++++++
 kernel-shared/print-tree.c |  1 +
 mkfs/common.c              |  9 +++++++++
 mkfs/main.c                |  5 +++++
 7 files changed, 51 insertions(+)

diff --git a/common/fsfeatures.c b/common/fsfeatures.c
index 057519c50c54..63258262437d 100644
--- a/common/fsfeatures.c
+++ b/common/fsfeatures.c
@@ -181,6 +181,17 @@ static const struct btrfs_feature runtime_features[] = {
 		VERSION_NULL(default),
 		.desc		= "extra super block reserved space for each device"
 	},
+#if EXPERIMENTAL
+	{
+		.name		= "write-intent-bitmap",
+		.flag		= BTRFS_RUNTIME_FEATURE_WRITE_INTENT_BITMAP,
+		.sysfs_name = "write_intent_bitmap",
+		VERSION_NULL(compat),
+		VERSION_NULL(safe),
+		VERSION_NULL(default),
+		.desc		= "write intent bitmap"
+	},
+#endif
 	/* Keep this one last */
 	{
 		.name = "list-all",
diff --git a/common/fsfeatures.h b/common/fsfeatures.h
index 565873ec0e4f..c48aa5d05ac0 100644
--- a/common/fsfeatures.h
+++ b/common/fsfeatures.h
@@ -46,6 +46,7 @@
 #define BTRFS_RUNTIME_FEATURE_QUOTA		(1ULL << 0)
 #define BTRFS_RUNTIME_FEATURE_FREE_SPACE_TREE	(1ULL << 1)
 #define BTRFS_RUNTIME_FEATURE_EXTRA_SUPER_RESERVED (1ULL << 2)
+#define BTRFS_RUNTIME_FEATURE_WRITE_INTENT_BITMAP  (1ULL << 3)
 
 void btrfs_list_all_fs_features(u64 mask_disallowed);
 void btrfs_list_all_runtime_features(u64 mask_disallowed);
diff --git a/kernel-shared/ctree.h b/kernel-shared/ctree.h
index 0b4a8d60ceb4..c746c0d3ab89 100644
--- a/kernel-shared/ctree.h
+++ b/kernel-shared/ctree.h
@@ -502,6 +502,13 @@ BUILD_ASSERT(sizeof(struct btrfs_super_block) == BTRFS_SUPER_INFO_SIZE);
  */
 #define BTRFS_FEATURE_COMPAT_RO_EXTRA_SUPER_RESERVED	(1ULL << 3)
 
+/*
+ * Allow btrfs to have per-device write-intent bitmap.
+ * Will be utilized to close the RAID56 write-hole (by forced scrub for dirty
+ * partial written stripes at mount time).
+ */
+#define BTRFS_FEATURE_COMPAT_RO_WRITE_INTENT_BITMAP	(1ULL << 4)
+
 #define BTRFS_FEATURE_INCOMPAT_MIXED_BACKREF	(1ULL << 0)
 #define BTRFS_FEATURE_INCOMPAT_DEFAULT_SUBVOL	(1ULL << 1)
 #define BTRFS_FEATURE_INCOMPAT_MIXED_GROUPS	(1ULL << 2)
@@ -524,6 +531,13 @@ BUILD_ASSERT(sizeof(struct btrfs_super_block) == BTRFS_SUPER_INFO_SIZE);
 
 #define BTRFS_FEATURE_COMPAT_SUPP		0ULL
 
+#if EXPERIMENTAL
+#define BTRFS_FEATURE_COMPAT_RO_SUPP			\
+	(BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE |	\
+	 BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE_VALID |\
+	 BTRFS_FEATURE_COMPAT_RO_EXTRA_SUPER_RESERVED |	\
+	 BTRFS_FEATURE_COMPAT_RO_WRITE_INTENT_BITMAP)
+#else
 /*
  * The FREE_SPACE_TREE and FREE_SPACE_TREE_VALID compat_ro bits must not be
  * added here until read-write support for the free space tree is implemented in
@@ -533,6 +547,7 @@ BUILD_ASSERT(sizeof(struct btrfs_super_block) == BTRFS_SUPER_INFO_SIZE);
 	(BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE |	\
 	 BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE_VALID |\
 	 BTRFS_FEATURE_COMPAT_RO_EXTRA_SUPER_RESERVED)
+#endif
 
 #if EXPERIMENTAL
 #define BTRFS_FEATURE_INCOMPAT_SUPP			\
diff --git a/kernel-shared/disk-io.c b/kernel-shared/disk-io.c
index bf3ea5e63165..843fe0e73940 100644
--- a/kernel-shared/disk-io.c
+++ b/kernel-shared/disk-io.c
@@ -1848,6 +1848,15 @@ int btrfs_check_super(struct btrfs_super_block *sb, unsigned sbflags)
 		}
 	}
 
+	if (btrfs_super_compat_ro_flags(sb) &
+	    BTRFS_FEATURE_COMPAT_RO_WRITE_INTENT_BITMAP &&
+	    !(btrfs_super_compat_ro_flags(sb) &
+	      BTRFS_FEATURE_COMPAT_RO_EXTRA_SUPER_RESERVED)) {
+		error(
+"write intent bitmap feature enabled without extra super reserved feature");
+		goto error_out;
+	}
+
 	if (btrfs_super_compat_ro_flags(sb) &
 	    BTRFS_FEATURE_COMPAT_RO_EXTRA_SUPER_RESERVED &&
 	    btrfs_super_reserved_bytes(sb) < BTRFS_BLOCK_RESERVED_1M_FOR_SUPER) {
diff --git a/kernel-shared/print-tree.c b/kernel-shared/print-tree.c
index 918ebe02144a..55875a7bc2d3 100644
--- a/kernel-shared/print-tree.c
+++ b/kernel-shared/print-tree.c
@@ -1669,6 +1669,7 @@ static struct readable_flag_entry compat_ro_flags_array[] = {
 	DEF_COMPAT_RO_FLAG_ENTRY(FREE_SPACE_TREE),
 	DEF_COMPAT_RO_FLAG_ENTRY(FREE_SPACE_TREE_VALID),
 	DEF_COMPAT_RO_FLAG_ENTRY(EXTRA_SUPER_RESERVED),
+	DEF_COMPAT_RO_FLAG_ENTRY(WRITE_INTENT_BITMAP),
 };
 static const int compat_ro_flags_num = sizeof(compat_ro_flags_array) /
 				       sizeof(struct readable_flag_entry);
diff --git a/mkfs/common.c b/mkfs/common.c
index f3c00f08826d..98da10718e7b 100644
--- a/mkfs/common.c
+++ b/mkfs/common.c
@@ -316,6 +316,8 @@ int make_btrfs(int fd, struct btrfs_mkfs_config *cfg)
 				 BTRFS_FEATURE_INCOMPAT_EXTENT_TREE_V2);
 	bool extra_super_reserved = !!(cfg->runtime_features &
 				 BTRFS_RUNTIME_FEATURE_EXTRA_SUPER_RESERVED);
+	bool write_intent_bitmap = !!(cfg->runtime_features &
+				 BTRFS_RUNTIME_FEATURE_WRITE_INTENT_BITMAP);
 
 	/* Don't include the free space tree in the blocks to process. */
 	if (!free_space_tree)
@@ -657,6 +659,13 @@ int make_btrfs(int fd, struct btrfs_mkfs_config *cfg)
 		btrfs_set_super_reserved_bytes(&super, system_group_offset);
 	}
 
+	if (write_intent_bitmap) {
+		u64 ro_flags = btrfs_super_compat_ro_flags(&super) |
+			       BTRFS_FEATURE_COMPAT_RO_WRITE_INTENT_BITMAP;
+
+		btrfs_set_super_compat_ro_flags(&super, ro_flags);
+	}
+
 	if (extent_tree_v2) {
 		ret = create_block_group_tree(fd, cfg, buf,
 					      system_group_offset,
diff --git a/mkfs/main.c b/mkfs/main.c
index 4ccf4e161d06..049d6f1dae2a 100644
--- a/mkfs/main.c
+++ b/mkfs/main.c
@@ -1248,6 +1248,11 @@ int BOX_MAIN(mkfs)(int argc, char **argv)
 		error("extra-super-reserved runtime feature conflicts with zoned devices");
 		exit(1);
 	}
+
+	/* Write intent bitmap must has extra reserved space. */
+	if (runtime_features & BTRFS_RUNTIME_FEATURE_WRITE_INTENT_BITMAP)
+		runtime_features |= BTRFS_RUNTIME_FEATURE_EXTRA_SUPER_RESERVED;
+
 	/*
 	* Set default profiles according to number of added devices.
 	* For mixed groups defaults are single/single.
-- 
2.36.1