[PATCH] btrfs: Introduce compile time structure size check

[Qu Wenruo <wqu@suse.com>]

Introduce a new macro based compile time check for ioctl structures.

The new macro is BTRFS_ASSERT_SIZE(), which is mostly copied from
VMMDEV_ASSERT_SIZE().

Such check is only added to structure pended to power of 2.
And exposed one structure, btrfs_ioctl_get_dev_stats() is not aligned
well.
The misalign is introduced by commit b27f7c0c150f ("btrfs: join DEV_STATS
ioctls to one").

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 include/uapi/linux/btrfs.h | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index 5ca1d21fc4a7..be1213c10080 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -22,6 +22,14 @@
 #include <linux/types.h>
 #include <linux/ioctl.h>
 
+/*
+ * Compile time check on structure size, same method as
+ * VMMDEV_ASSERT_SIZE() from linux/vbox_vmmdev_types.h, to trigger a negative
+ * array size at compile time if size doesn't match.
+ */
+#define BTRFS_ASSERT_SIZE(type, size) \
+	typedef char type ## _asrt_size[1 - 2 * !!(sizeof(struct type) != (size))]
+
 #define BTRFS_IOCTL_MAGIC 0x94
 #define BTRFS_VOL_NAME_MAX 255
 #define BTRFS_LABEL_SIZE 256
@@ -32,6 +40,7 @@ struct btrfs_ioctl_vol_args {
 	__s64 fd;
 	char name[BTRFS_PATH_NAME_MAX + 1];
 };
+BTRFS_ASSERT_SIZE(btrfs_ioctl_vol_args, 4096);
 
 #define BTRFS_DEVICE_PATH_NAME_MAX	1024
 #define BTRFS_SUBVOL_NAME_MAX 		4039
@@ -171,6 +180,7 @@ struct btrfs_ioctl_scrub_args {
 	/* pad to 1k */
 	__u64 unused[(1024-32-sizeof(struct btrfs_scrub_progress))/8];
 };
+BTRFS_ASSERT_SIZE(btrfs_ioctl_scrub_args, 1024);
 
 #define BTRFS_IOCTL_DEV_REPLACE_CONT_READING_FROM_SRCDEV_MODE_ALWAYS	0
 #define BTRFS_IOCTL_DEV_REPLACE_CONT_READING_FROM_SRCDEV_MODE_AVOID	1
@@ -223,6 +233,7 @@ struct btrfs_ioctl_dev_info_args {
 	__u64 unused[379];			/* pad to 4k */
 	__u8 path[BTRFS_DEVICE_PATH_NAME_MAX];	/* out */
 };
+BTRFS_ASSERT_SIZE(btrfs_ioctl_dev_info_args, 4096);
 
 struct btrfs_ioctl_fs_info_args {
 	__u64 max_id;				/* out */
@@ -234,6 +245,7 @@ struct btrfs_ioctl_fs_info_args {
 	__u32 reserved32;
 	__u64 reserved[122];			/* pad to 1k */
 };
+BTRFS_ASSERT_SIZE(btrfs_ioctl_fs_info_args, 1024);
 
 /*
  * feature flags
@@ -414,6 +426,7 @@ struct btrfs_ioctl_balance_args {
 
 	__u64 unused[72];			/* pad to 1k */
 };
+BTRFS_ASSERT_SIZE(btrfs_ioctl_balance_args, 1024);
 
 #define BTRFS_INO_LOOKUP_PATH_MAX 4080
 struct btrfs_ioctl_ino_lookup_args {
@@ -421,6 +434,7 @@ struct btrfs_ioctl_ino_lookup_args {
 	__u64 objectid;
 	char name[BTRFS_INO_LOOKUP_PATH_MAX];
 };
+BTRFS_ASSERT_SIZE(btrfs_ioctl_ino_lookup_args, 4096);
 
 #define BTRFS_INO_LOOKUP_USER_PATH_MAX (4080 - BTRFS_VOL_NAME_MAX - 1)
 struct btrfs_ioctl_ino_lookup_user_args {
@@ -436,6 +450,7 @@ struct btrfs_ioctl_ino_lookup_user_args {
 	 */
 	char path[BTRFS_INO_LOOKUP_USER_PATH_MAX];
 };
+BTRFS_ASSERT_SIZE(btrfs_ioctl_ino_lookup_args, 4096);
 
 /* Search criteria for the btrfs SEARCH ioctl family. */
 struct btrfs_ioctl_search_key {
@@ -664,8 +679,9 @@ struct btrfs_ioctl_get_dev_stats {
 	/* out values: */
 	__u64 values[BTRFS_DEV_STAT_VALUES_MAX];
 
-	__u64 unused[128 - 2 - BTRFS_DEV_STAT_VALUES_MAX]; /* pad to 1k */
+	__u64 unused[128 - 3 - BTRFS_DEV_STAT_VALUES_MAX]; /* pad to 1k */
 };
+BTRFS_ASSERT_SIZE(btrfs_ioctl_get_dev_stats, 1024);
 
 #define BTRFS_QUOTA_CTL_ENABLE	1
 #define BTRFS_QUOTA_CTL_DISABLE	2
-- 
2.18.0