Re: [PATCH v2 0/2] kdump: simplify code

[Matthew Wilcox <willy@xxxxxxxxxxxxx>]

On Tue, Dec 14, 2021 at 06:03:11PM +0800, Tiezhu Yang wrote:
> On 12/13/2021 10:43 PM, Matthew Wilcox wrote:
> > On Mon, Dec 13, 2021 at 08:30:33AM +0000, David Laight wrote:
> > > From: Matthew Wilcox
> > > > Sent: 12 December 2021 11:48
> > > > 
> > > > On Sat, Dec 11, 2021 at 05:53:46PM +0000, David Laight wrote:
> > > > > From: Tiezhu Yang
> > > > > > Sent: 11 December 2021 03:33
> > > > > > 
> > > > > > v2:
> > > > > >   -- add copy_to_user_or_kernel() in lib/usercopy.c
> > > > > >   -- define userbuf as bool type
> > > > > 
> > > > > Instead of having a flag to indicate whether the buffer is user or kernel,
> > > > > would it be better to have two separate buffer pointers.
> > > > > One for a user space buffer, the other for a kernel space buffer.
> > > > > Exactly one of the buffers should always be NULL.
> > > > 
> > > > No.  You should be using an iov_iter instead.  See
> > > > https://lore.kernel.org/all/Ya4bdB0UBJCZhUSo@xxxxxxxxxxxxxxxxxxxx/
> > > > for a start on this.
> > > 
> > > iov_iter gets horribly expensive...
> > 
> > Oh, right.  Reading the kcore is a high-performance path, my mistake.
> > 
> 
> Hi,
> 
> Thank you for your discussions.
> 
> The intention of this patchset is to simplify the related code with no
> functional changes and no side effects.
> 
> At this moment, if you are OK, I will send v3 used with inline function
> copy_to_user_or_kernel() to keep it simple, maybe other more changes can
> be done in the future if no any side effect.

That would be pointless.  I already sent a series to remove this,
which you were cc'd on.