sparse: ARRAY_SIZE and sparse array initialization

[Hans Verkuil <hverkuil@xs4all.nl>]

Hmm, interesting. Twice 'sparse' in the same subject line with different meanings :-)

This is another sparse error I get with drivers/media/v4l2-core/v4l2-ioctl.c:

drivers/media/v4l2-core/v4l2-ioctl.c:424:9: error: cannot size expression

(there are more of those in drivers/media, all with the same cause).

This sparse (the tool) error occurs because of sparse (C language) array initialization
in combination with ARRAY_SIZE:

static const char *v4l2_memory_names[] = {
        [V4L2_MEMORY_MMAP]    = "mmap",
        [V4L2_MEMORY_USERPTR] = "userptr",
        [V4L2_MEMORY_OVERLAY] = "overlay",
        [V4L2_MEMORY_DMABUF] = "dmabuf",
};

#define prt_names(a, arr) (((unsigned)(a)) < ARRAY_SIZE(arr) ? arr[a] : "unknown")

static void v4l_print_requestbuffers(const void *arg, bool write_only)
{
        const struct v4l2_requestbuffers *p = arg;

        pr_cont("count=%d, type=%s, memory=%s\n",
                p->count,
                prt_names(p->type, v4l2_type_names),
                prt_names(p->memory, v4l2_memory_names));
}

I could change v4l2_memory_names to:

static const char *v4l2_memory_names[V4L2_MEMORY_DMABUF + 1] = {

and the error goes away.

I'm actually not sure if this is a sparse bug or a feature.

If it is a feature then the error message is definitely wrong, since the size is
perfectly well defined. As an aside: the error message is pretty vague IMHO.

Regards,

	Hans