On 22/07/19 5:54 PM, Paul Kocialkowski wrote:
Hi,
On Mon 22 Jul 19, 12:12, Jeremy Sowden wrote:
On 2019-07-22, at 11:36:51 +0530, Nishka Dasgupta wrote:
Typecast as bool the return value of cedrus_find_format in
cedrus_check_format as the return value of cedrus_check_format is
always treated like a boolean value.
Signed-off-by: Nishka Dasgupta <nishkadg.linux@xxxxxxxxx>
---
Changes in v2:
- Add !! to the returned pointer to ensure that the return value is
always either true or false, and never a non-zero value other than
true.
drivers/staging/media/sunxi/cedrus/cedrus_video.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_video.c b/drivers/staging/media/sunxi/cedrus/cedrus_video.c
index e2b530b1a956..b731745f21f8 100644
--- a/drivers/staging/media/sunxi/cedrus/cedrus_video.c
+++ b/drivers/staging/media/sunxi/cedrus/cedrus_video.c
@@ -86,7 +86,7 @@ static struct cedrus_format *cedrus_find_format(u32 pixelformat, u32 directions,
static bool cedrus_check_format(u32 pixelformat, u32 directions,
unsigned int capabilities)
{
- return cedrus_find_format(pixelformat, directions, capabilities);
+ return !!(bool)cedrus_find_format(pixelformat, directions, capabilities);
}
I think the original was fine. The return value of cedrus_find_format
will be automatically converted to bool before being returned from
cedrus_check_format since that is the return-type of the function, and
the result of converting any non-zero value to bool is 1.
Okay I was a bit unsure about that and wanted to play it on the safe side
without really looking it up, but that gave me the occasion to verify.
From what I could find (from my GNU system's /usr/include/unistring/stdbool.h):
Limitations of this substitute, when used in a C89 environment:
- In C99, casts and automatic conversions to '_Bool' or 'bool' are
performed in such a way that every nonzero value gets converted
to 'true', and zero gets converted to 'false'. This doesn't work
with this substitute. With this substitute, only the values 0 and 1
give the expected result when converted to _Bool' or 'bool'.
So since the kernel is built for C89 (unless I'm mistaken), I don't think the
compiler provides any guarantee about bool values being converted to 1 when
they are non-zero. As a result, I think it's best to be careful.
However, I'm not sure I really see what cocinelle was unhappy about. You
mentionned single-line functions, but I don't see how that can be a problem.
It's not a problem per se. I'm just working on a cleanup project for
which I went through all of staging replacing single-line functions with
what they were calling. In some cases that makes it easier to figure out
what a particular function call does, since the called function actually
does something itself instead of just calling a different function?
This function was also flagged as one such potentially-removable
function by Coccinelle; but in order to do the same replacement that I'd
done in other staging drivers, I thought I would do something about the
type mismatch first, especially since find_format doesn't appear to be
used anywhere else.
However, now I won't remove check_format and replace it with find_format
as I'd originally planned, since you've said that isn't necessary here.
That leaves the return type issue.
So in the end, I think we should keep the !! and drop the (bool) cast if there's
no particular warning about it.
Should I send a version 3 that does this?
Thanking you,
Nishka
What do you think?
Cheers,
Paul
static void cedrus_prepare_format(struct v4l2_pix_format *pix_fmt)
--
2.19.1
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