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.