Hi Gerd,
On Tuesday, 11 September 2018 09:50:14 EEST Gerd Hoffmann wrote:
> Hi,
>
> >> +#define UDMABUF_CREATE _IOW('u', 0x42, struct udmabuf_create)
> >
> > Why do you start at 0x42 if you reserve the 0x40-0x4f range ?
>
> No particular strong reason, just that using 42 was less boring than
> starting with 0x40.
>
> >> +#define UDMABUF_CREATE_LIST _IOW('u', 0x43, struct
> >> udmabuf_create_list)
> >
> > Where's the documentation ? :-)
>
> Isn't it simple enough?
No kernel UAPI is simple enough to get away without documenting it.
> But, well, yes, I guess I can add some kerneldoc comments.
>
> >> +static int udmabuf_vm_fault(struct vm_fault *vmf)
> >> +{
> >> + struct vm_area_struct *vma = vmf->vma;
> >> + struct udmabuf *ubuf = vma->vm_private_data;
> >> +
> >> + if (WARN_ON(vmf->pgoff >= ubuf->pagecount))
> >> + return VM_FAULT_SIGBUS;
> >
> > Just curious, when do you expect this to happen ?
>
> It should not. If it actually happens it would be a bug somewhere,
> thats why the WARN_ON.
But you seem to consider that this condition that should never happen still
has a high enough chance of happening that it's worth a WARN_ON(). I was
wondering why this one in particular, and not other conditions that also can't
happen and are not checked through the code.
> >> + struct udmabuf *ubuf;
> >>
> >> + ubuf = kzalloc(sizeof(struct udmabuf), GFP_KERNEL);
> >
> > sizeof(*ubuf)
>
> Why? Should not make a difference ...
Because the day we replace
struct udmabuf *ubuf;
with
struct udmabuf_ext *ubuf;
and forget to change the next line, we'll introduce a bug. That's why
sizeof(variable) is preferred over sizeof(type). Another reason is that I can
easily see that
ubuf = kzalloc(sizeof(*ubuf), GFP_KERNEL);
is correct, while using sizeof(type) requires me to go and look up the
declaration of the variable.
> >> + memfd = fget(list[i].memfd);
> >> + if (!memfd)
> >> + goto err_put_pages;
> >> + if (!shmem_mapping(file_inode(memfd)->i_mapping))
> >> + goto err_put_pages;
> >> + seals = memfd_fcntl(memfd, F_GET_SEALS, 0);
> >> + if (seals == -EINVAL ||
> >> + (seals & SEALS_WANTED) != SEALS_WANTED ||
> >> + (seals & SEALS_DENIED) != 0)
> >> + goto err_put_pages;
> >
> > All these conditions will return -EINVAL. I'm not familiar with the memfd
> > API, should some error conditions return a different error code to make
> > them distinguishable by userspace ?
>
> Hmm, I guess EBADFD would be reasonable in case the file handle isn't a
> memfd. Other suggestions?
I'll let others comment on this as I don't feel qualified to pick proper error
codes, not being familiar with the memfd API.
> I'll prepare a fixup patch series addressing most of the other
> review comments.
--
Regards,
Laurent Pinchart
