On 2021/10/21 20:40, David Sterba wrote:

On Thu, Oct 21, 2021 at 09:40:18AM +0800, Qu Wenruo wrote:

quoted

Just like kernel change, pad struct btrfs_super_block to 4096 bytes.

Signed-off-by: Qu Wenruo <redacted>
---
  kernel-shared/ctree.h   | 7 +++++++
  kernel-shared/disk-io.h | 3 ---
  2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/kernel-shared/ctree.h b/kernel-shared/ctree.h
index 563ea50b3587..6451690ce4fa 100644
--- a/kernel-shared/ctree.h
+++ b/kernel-shared/ctree.h

@@ -406,6 +406,9 @@ struct btrfs_root_backup {
  	u8 unused_8[10];
  } __attribute__ ((__packed__));

+#define BTRFS_SUPER_INFO_OFFSET SZ_64K
+#define BTRFS_SUPER_INFO_SIZE 4096
+
  /*
   * the super block basically lists the main trees of the FS
   * it currently lacks any block count etc etc

@@ -456,8 +459,12 @@ struct btrfs_super_block {
  	__le64 reserved[28];
  	u8 sys_chunk_array[BTRFS_SYSTEM_CHUNK_ARRAY_SIZE];
  	struct btrfs_root_backup super_roots[BTRFS_NUM_BACKUP_ROOTS];
+	/* Padded to 4096 bytes */
+	u8 padding[565];
  } __attribute__ ((__packed__));

+static_assert(sizeof(struct btrfs_super_block) == BTRFS_SUPER_INFO_SIZE);

Using static_assert breaks build on musl (you can verify that by running
ci/ci-build-musl if you have docker installed and set up).

There already is macro BUILD_ASSERT used in ioctl.h, eventually we can
copy the static_assert from kernel or use _Static_assert directly.

Mind to fix that on your side?

As I don't yet have any building environment for musl to verify the
failure or fix.

Thanks,
Qu