[PATCH 7/7] xfs: Replace one-element arrays with flexible-array members

[Christoph Hellwig <hch@lst.de>]

From: "Gustavo A. R. Silva" <gustavoars@kernel.org>

There is a regular need in the kernel to provide a way to declare having
a dynamically sized set of trailing elements in a structure. Kernel code
should always use “flexible array members”[1] for these cases. The older
style of one-element or zero-length arrays should no longer be used[2].

Refactor the code according to the use of flexible-array members in
multiple structures, instead of one-element arrays. Also, make use of
the new struct_size() helper to properly calculate the size of some
structures that contain flexible-array members.

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.9/process/deprecated.html#zero-length-and-one-element-arrays

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
[hch: rebased on top of the previous cleanups]
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/xfs/libxfs/xfs_log_format.h | 6 +++---
 fs/xfs/xfs_extfree_item.c      | 9 +++------
 fs/xfs/xfs_extfree_item.h      | 4 ++--
 fs/xfs/xfs_ondisk.h            | 6 +++---
 4 files changed, 11 insertions(+), 14 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_log_format.h b/fs/xfs/libxfs/xfs_log_format.h
index 639035052b4f65..9b218c30659ad7 100644
--- a/fs/xfs/libxfs/xfs_log_format.h
+++ b/fs/xfs/libxfs/xfs_log_format.h
@@ -559,7 +559,7 @@ struct xfs_efi_log_format {
 	uint16_t		efi_size;	/* size of this item */
 	uint32_t		efi_nextents;	/* # extents to free */
 	uint64_t		efi_id;		/* efi identifier */
-	struct xfs_extent	efi_extents[1];	/* array of extents to free */
+	struct xfs_extent	efi_extents[];	/* array of extents to free */
 };
 
 /*
@@ -577,7 +577,7 @@ struct xfs_efi_log_format_32 {
 	uint16_t		efi_size;	/* size of this item */
 	uint32_t		efi_nextents;	/* # extents to free */
 	uint64_t		efi_id;		/* efi identifier */
-	struct xfs_extent_32	efi_extents[1];	/* array of extents to free */
+	struct xfs_extent_32	efi_extents[];	/* array of extents to free */
 } __attribute__((packed));
 
 /*
@@ -590,7 +590,7 @@ struct xfs_efd_log_format {
 	uint16_t		efd_size;	/* size of this item */
 	uint32_t		efd_nextents;	/* # of extents freed */
 	uint64_t		efd_efi_id;	/* id of corresponding efi */
-	struct xfs_extent	efd_extents[1];	/* array of extents freed */
+	struct xfs_extent	efd_extents[];	/* array of extents freed */
 };
 
 /*
diff --git a/fs/xfs/xfs_extfree_item.c b/fs/xfs/xfs_extfree_item.c
index a2abdfd3d076bf..8bea9c9ecf2042 100644
--- a/fs/xfs/xfs_extfree_item.c
+++ b/fs/xfs/xfs_extfree_item.c
@@ -73,8 +73,7 @@ static inline int
 xfs_efi_log_item_sizeof(
 	struct xfs_efi_log_format *elf)
 {
-	return sizeof(*elf) +
-	       (elf->efi_nextents - 1) * sizeof(struct xfs_extent);
+	return struct_size(elf, efi_extents, elf->efi_nextents);
 }
 
 STATIC void
@@ -194,8 +193,7 @@ static inline int
 xfs_efd_log_item_sizeof(
 	struct xfs_efd_log_format *elf)
 {
-	return sizeof(struct xfs_efd_log_format) +
-	       (elf->efd_nextents - 1) * sizeof(struct xfs_extent);
+	return struct_size(elf, efd_extents, elf->efd_nextents);
 }
 
 STATIC void
@@ -636,8 +634,7 @@ xfs_efi_copy_format_32(
 	struct xfs_efi_log_format_32	*src = buf->i_addr;
 	unsigned int			i;
 
-	if (buf->i_len != sizeof(*src) +
-	    (src->efi_nextents - 1) * sizeof(struct xfs_extent_32)) {
+	if (buf->i_len != struct_size(src, efi_extents, src->efi_nextents)) {
 		XFS_ERROR_REPORT(__func__, XFS_ERRLEVEL_LOW, NULL);
 		return -EFSCORRUPTED;
 	}
diff --git a/fs/xfs/xfs_extfree_item.h b/fs/xfs/xfs_extfree_item.h
index 3bb62ef525f2e0..a01ce86145bb64 100644
--- a/fs/xfs/xfs_extfree_item.h
+++ b/fs/xfs/xfs_extfree_item.h
@@ -55,7 +55,7 @@ struct xfs_efi_log_item {
 static inline int xfs_efi_item_sizeof(unsigned int nextents)
 {
 	return sizeof(struct xfs_efi_log_item) +
-		(nextents - 1) * sizeof(struct xfs_extent);
+		nextents * sizeof(struct xfs_extent);
 }
 
 /*
@@ -73,7 +73,7 @@ struct xfs_efd_log_item {
 static inline int xfs_efd_item_sizeof(unsigned int nextents)
 {
 	return sizeof(struct xfs_efd_log_item) +
-		(nextents - 1) * sizeof(struct xfs_extent);
+		nextents * sizeof(struct xfs_extent);
 }
 
 /*
diff --git a/fs/xfs/xfs_ondisk.h b/fs/xfs/xfs_ondisk.h
index 739476f7dffa21..fa4b590671bf58 100644
--- a/fs/xfs/xfs_ondisk.h
+++ b/fs/xfs/xfs_ondisk.h
@@ -118,9 +118,9 @@ xfs_check_ondisk_structs(void)
 	/* log structures */
 	XFS_CHECK_STRUCT_SIZE(struct xfs_buf_log_format,	88);
 	XFS_CHECK_STRUCT_SIZE(struct xfs_dq_logformat,		24);
-	XFS_CHECK_STRUCT_SIZE(struct xfs_efd_log_format,	32);
-	XFS_CHECK_STRUCT_SIZE(struct xfs_efi_log_format,	32);
-	XFS_CHECK_STRUCT_SIZE(struct xfs_efi_log_format_32,	28);
+	XFS_CHECK_STRUCT_SIZE(struct xfs_efd_log_format,	16);
+	XFS_CHECK_STRUCT_SIZE(struct xfs_efi_log_format,	16);
+	XFS_CHECK_STRUCT_SIZE(struct xfs_efi_log_format_32,	16);
 	XFS_CHECK_STRUCT_SIZE(struct xfs_extent,		16);
 	XFS_CHECK_STRUCT_SIZE(struct xfs_extent_32,		12);
 	XFS_CHECK_STRUCT_SIZE(struct xfs_log_dinode,		176);
-- 
2.30.1