btrfs: validate negative error number passed to btrfs_abort_transaction()

In preparation to encode more information to the error value add a step
that verifies if the value is valid (i.e. < 0). This works for
compile-time and runtime (in debugging mode).

The compile-time check recognizes direct constants and defines an array
type. An invalid condition leads to negative array size which is caught
by compiler.

The runtime check constructs the array type from the condition and only
verifies the correct size, as we don't need to tweak the size to be
negative.

The sizeof() expressions do not generate any code. In the debugging
config the warning adds about 9KiB of btrfs.ko code size.

The array size trick is needed as we can't use static_array(), not even
with __builtin_constant_p().

Sample error message:

In file included from inode.c:40:
inode.c: In function ‘__cow_file_range_inline’:
transaction.h:261:26: error: size of unnamed array is negative
  261 |         (void)sizeof(char[-!(__builtin_constant_p(error) ? (error) < 0 : 1)]);  \
      |                          ^
transaction.h:275:9: note: in expansion of macro ‘VERIFY_NEGATIVE_ERROR’
  275 |         VERIFY_NEGATIVE_ERROR(error);                           \
      |         ^~~~~~~~~~~~~~~~~~~~~
inode.c:665:17: note: in expansion of macro ‘btrfs_abort_transaction’
  665 |                 btrfs_abort_transaction(trans, 17);
      |                 ^~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: David Sterba <dsterba@suse.com>

0 files changed, 0 insertions, 0 deletions