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SubjectRe: [PATCH] dm: writecache: fix format string warning


On Mon, 28 May 2018, Arnd Bergmann wrote:

> The return type of ACCESS_ONCE is configuration dependent and may be either
> 'int' or 'long int' for the writecache_has_error() macro, so we get a warning
> like this for either format string:

__builtin_expect returns always long, see the GCC documentation (it used
to return int in very old gcc versions such as 2.96).

I think this is a bug in the macro __branch_check__. The variable ______r
should be long, but it is int. This bug may cause misbehavior of other
kernel parts (i.e. truncation of long value to int), so it should be fixed
in __branch_check__ - not in dm-writecache.

Mikulas

> In file included from drivers/md/dm-writecache.c:8:
> drivers/md/dm-writecache.c: In function 'writecache_status':
> drivers/md/dm-writecache.c:2227:10: error: format '%ld' expects argument of type 'long int', but argument 4 has type 'int' [-Werror=format=]
> DMEMIT("%ld %llu %llu %llu", writecache_has_error(wc),
> ^~~~~~~~~~~~~~~~~~~~
> include/linux/device-mapper.h:549:46: note: in definition of macro 'DMEMIT'
> 0 : scnprintf(result + sz, maxlen - sz, x))
> ^
>
> The code is otherwise correct, so we just need to shut up the warning,
> which can be done using an extra type cast.
>
> Fixes: bb15b431d650 ("dm: add writecache target")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> drivers/md/dm-writecache.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c
> index 1ef06e738eb6..772ac3a57287 100644
> --- a/drivers/md/dm-writecache.c
> +++ b/drivers/md/dm-writecache.c
> @@ -2224,7 +2224,7 @@ static void writecache_status(struct dm_target *ti, status_type_t type,
>
> switch (type) {
> case STATUSTYPE_INFO:
> - DMEMIT("%ld %llu %llu %llu", writecache_has_error(wc),
> + DMEMIT("%ld %llu %llu %llu", (long)writecache_has_error(wc),
> (unsigned long long)wc->n_blocks, (unsigned long long)wc->freelist_size,
> (unsigned long long)wc->writeback_size);
> break;
> --
> 2.9.0
>

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