On Sun, 2020-08-23 at 16:21 +0100, Matthew Wilcox wrote:
> On Wed, Aug 19, 2020 at 10:14:11AM +0200, Giuseppe Scrivano wrote:
> > > > - cft->file_offset = offsetof(struct hugetlb_cgroup,
> > > > events_file[idx]),
> > > > + cft->file_offset = offsetof(struct hugetlb_cgroup,
> > > > events_file[idx]);
> > > > cft->flags = CFTYPE_NOT_ON_ROOT;
> >
> > I think in this case having two expressions as part of the same
> > statement is equivalent to having two separate statements. Both
> > cft->file_offset and cft->flags get the expected value.
>
> That's not how the comma operator works.
>
> It will evaluate offsetof(struct hugetlb_cgroup, events_file[idx]) and
> then discard the result. Since it has no side-effects, this is effectively
> doing:
>
> cft->file_offset = cft->flags = CFTYPE_NOT_ON_ROOT;
$ gcc -x c -
#include <stdio.h>
#include <stdlib.h>
struct foo {
int a;
char b[50];
};
int main(int argc, char **argv)
{
int a;
int b;
a = sizeof(struct foo), b = 1;
printf("a: %d, b: %d\n", a, b);
return 0;
}
$ ./a.out
a: 56, b: 1
