treewide: uapi: Replace zero-length arrays with flexible-array members

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].

This code was transformed with the help of Coccinelle:
(linux-5.19-rc2$ spatch --jobs $(getconf _NPROCESSORS_ONLN) --sp-file script.cocci --include-headers --dir . > output.patch)

@@
identifier S, member, array;
type T1, T2;
@@

struct S {
  ...
  T1 member;
  T2 array[
- 0
  ];
};

-fstrict-flex-arrays=3 is coming and we need to land these changes
to prevent issues like these in the short future:

../fs/minix/dir.c:337:3: warning: 'strcpy' will always overflow; destination buffer has size 0,
but the source string has length 2 (including NUL byte) [-Wfortify-source]
		strcpy(de3->name, ".");
		^

Since these are all [0] to [] changes, the risk to UAPI is nearly zero. If
this breaks anything, we can use a union with a new member name.

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.16/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/78
Build-tested-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/lkml/62b675ec.wKX6AOZ6cbE71vtF%25lkp@intel.com/
Acked-by: Dan Williams <dan.j.williams@intel.com> # For ndctl.h
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

1 files changed, 4 insertions, 4 deletions

diff --git a/include/uapi/linux/dm-ioctl.h b/include/uapi/linux/dm-ioctl.h
index 2e9550fef90f..8c97d75f3104 100644
--- a/include/uapi/linux/dm-ioctl.h
+++ b/include/uapi/linux/dm-ioctl.h
@@ -182,7 +182,7 @@ struct dm_target_spec {
 struct dm_target_deps {
 	__u32 count;	/* Array size */
 	__u32 padding;	/* unused */
-	__u64 dev[0];	/* out */
+	__u64 dev[];	/* out */
 };
 
 /*
@@ -192,7 +192,7 @@ struct dm_name_list {
 	__u64 dev;
 	__u32 next;		/* offset to the next record from
 				   the _start_ of this */
-	char name[0];
+	char name[];
 
 	/*
 	 * The following members can be accessed by taking a pointer that
@@ -216,7 +216,7 @@ struct dm_target_versions {
         __u32 next;
         __u32 version[3];
 
-        char name[0];
+        char name[];
 };
 
 /*
@@ -225,7 +225,7 @@ struct dm_target_versions {
 struct dm_target_msg {
 	__u64 sector;	/* Device sector */
 
-	char message[0];
+	char message[];
 };
 
 /*