> On Apr 30, 2020, at 12:51 PM, Dan Williams <[email protected]> wrote: > > On Thu, Apr 30, 2020 at 12:23 PM Luck, Tony <[email protected]> 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.
