Re: [PATCH] rust: generalize userSliceReader to support any Vec

[Boqun Feng <boqun.feng@gmail.com>]

On Mon, Jan 06, 2025 at 02:34:13PM +0100, Alice Ryhl wrote:
[...]
> > > > ... what if the copy hit a page fault because the target memory (e.g. a
> > > > VVec) is not mapped? Would copy_from_user() handle this? Or would it
> > > > return a different error code than `EFAULT`?
> > > How could the memory not be mapped? A vector lets us obtain a &[u8] to the
> > > memory, which isn't valid if it's not mapped.
> > >
> >
> > I mistakenly thought that vmalloc()'d memory can be swapped out, which
> > is not the case. So you're right the memory must be mapped.
> >
> > But the usage question still exists: do you have an usage case for
> > reading userspace memory into a `VVec`?
> 
> I believe there's a use-case for a KVVec in Binder to avoid maximum
> sizes for a certain array.
> 

I see, thank you. `KVVec` makes a lot of senses here. I would still
suggest putting the details about the potential usage in the commit
message. Besides, Filipe, could you Cc memory management people next
time? Thanks!

Regards,
Boqun

> Alice