On Tue, Nov 15, 2016 at 11:00 AM, Vitaly Wool <vitalywool@xxxxxxxxx> wrote:
> Currently the whole kernel build will be stopped if the size of
> struct z3fold_header is greater than the size of one chunk, which
> is 64 bytes by default. This may stand in the way of automated
> test/debug builds so let's remove that and just fail the z3fold
> initialization in such case instead.
>
> Signed-off-by: Vitaly Wool <vitalywool@xxxxxxxxx>
> ---
> mm/z3fold.c | 11 ++++++++---
> 1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index 7ad70fa..ffd9353 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -870,10 +870,15 @@ MODULE_ALIAS("zpool-z3fold");
>
> static int __init init_z3fold(void)
> {
> - /* Make sure the z3fold header will fit in one chunk */
> - BUILD_BUG_ON(sizeof(struct z3fold_header) > ZHDR_SIZE_ALIGNED);
Nak. this is the wrong way to handle this. The build bug is there to
indicate to you that your patch makes the header too large, not as a
runtime check to disable everything.
The right way to handle it is to change the hardcoded assumption that
the header fits into a single chunk; e.g.:
#define ZHDR_SIZE_ALIGNED round_up(sizeof(struct z3fold_header), CHUNK_SIZE)
#define ZHDR_CHUNKS (ZHDR_SIZE_ALIGNED >> CHUNK_SHIFT)
then use ZHDR_CHUNKS in all places where it's currently assumed the
header is 1 chunk, e.g. in num_free_chunks:
if (zhdr->middle_chunks != 0) {
int nfree_before = zhdr->first_chunks ?
- 0 : zhdr->start_middle - 1;
+ 0 : zhdr->start_middle - ZHDR_CHUNKS;
after changing all needed places like that, the build bug isn't needed
anymore (unless we want to make sure the header isn't larger than some
arbitrary number N chunks)
> - zpool_register_driver(&z3fold_zpool_driver);
> + /* Fail the initialization if z3fold header won't fit in one chunk */
> + if (sizeof(struct z3fold_header) > ZHDR_SIZE_ALIGNED) {
> + pr_err("z3fold: z3fold_header size (%d) is bigger than "
> + "the chunk size (%d), can't proceed\n",
> + sizeof(struct z3fold_header) , ZHDR_SIZE_ALIGNED);
> + return -E2BIG;
> + }
>
> + zpool_register_driver(&z3fold_zpool_driver);
> return 0;
> }
>
> --
> 2.4.2
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