On Apr 30, 2020, at 12:51 PM, Dan Williams dan.j.williams@intel.com wrote:
On Thu, Apr 30, 2020 at 12:23 PM Luck, Tony tony.luck@intel.com wrote:
On Thu, Apr 30, 2020 at 11:42:20AM -0700, Andy Lutomirski wrote: I suppose there could be a consistent naming like this:
copy_from_user() copy_to_user()
copy_from_unchecked_kernel_address() [what probe_kernel_read() is] copy_to_unchecked_kernel_address() [what probe_kernel_write() is]
copy_from_fallible() [from a kernel address that can fail to a kernel address that can't fail] copy_to_fallible() [the opposite, but hopefully identical to memcpy() on x86]
copy_from_fallible_to_user() copy_from_user_to_fallible()
These names are fairly verbose and could probably be improved.
How about
try_copy_catch(void *dst, void *src, size_t count, int *fault)
returns number of bytes not-copied (like copy_to_user etc).
if return is not zero, "fault" tells you what type of fault cause the early stop (#PF, #MC).
I do like try_copy_catch() for the case when neither of the buffers are __user (like in the pmem driver) and _copy_to_iter_fallible() (plus all the helpers it implies) for the other cases.
copy_to_user_fallible copy_fallible_to_page copy_pipe_to_iter_fallible
...because the mmu-fault handling is an aspect of "_user" and fallible implies other source fault reasons. It does leave a gap if an architecture has a concept of a fallible write, but that seems like something that will be handled asynchronously and not subject to this interface.
I’m suspicious that, as a practical matter, x86 does have a fallible write. In particular, if a page fails and the memory failure code is notified, the page will be unmapped. At that point, an attempt to write to the failed fallible page will get #PF, and code that writes to it needs to be prepared to handle #PF. Perhaps copy_to_fallible(), etc can still return void, but I’m unconvinced the implementation can be the same as memcpy.