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SubjectRe: [PATCH] cgroup: add explicit cast and comment for return type conversion
Hello,

On Sun, May 24, 2015 at 03:07:52PM +0200, Nicholas Mc Guire wrote:
> Type-checking coccinelle spatches are being used to locate type mismatches
> between function signatures and return values in this case this produced:
> ./kernel/cgroup.c:2525 WARNING: return of wrong type
> ssize_t != size_t,
>
> Returning unsigned types converted to a signed type can be problematic
> but in this case the size_t is <= PATH_MAX which is less than ulong/2 so
> the conversion is safe - to make static code checking happy this is
> resolved by an explicit cast and appropriate comment.
>
> Patch was compile tested with x86_64_defconfig (implies CONFIG_CGROUPS=y)
>
> Patch is against 4.1-rc4 (localversion-next is -next-20150522)
>
> Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
> ---
>
> Not sure if "cleanups" like this are acceptable - in this case I did not
> find any better way to make static code checkers happy though.
>
> kernel/cgroup.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index b91177f..04de621 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -2523,7 +2523,11 @@ static ssize_t cgroup_release_agent_write(struct kernfs_open_file *of,
> sizeof(cgrp->root->release_agent_path));
> spin_unlock(&release_agent_path_lock);
> cgroup_kn_unlock(of->kn);
> - return nbytes;
> +
> + /* the path of the release notifier is <= PATH_MAX
> + * so "downsizing" to signed long is safe here
> + */
> + return (ssize_t)nbytes;

idk, does this actually help anything? This isn't different from any
other implicit type casts. Are we gonna convert all downward implicit
casts to be explicit?

Thanks.

--
tejun


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