Re: [PATCH 1/2] kdump: vmcore: move copy_to() from vmcore.c to uaccess.h

[Tiezhu Yang]

On 12/11/2021 12:59 AM, Andrew Morton wrote:
> On Fri, 10 Dec 2021 21:36:00 +0800 Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> wrote:
>
> > In arch/*/kernel/crash_dump*.c, there exist similar code about
> > copy_oldmem_page(), move copy_to() from vmcore.c to uaccess.h,
> > and then we can use copy_to() to simplify the related code.
> >
> > ...
> >
> > --- a/fs/proc/vmcore.c
> > +++ b/fs/proc/vmcore.c
> > @@ -238,20 +238,6 @@ copy_oldmem_page_encrypted(unsigned long pfn, char *buf, size_t csize,
> >  	return copy_oldmem_page(pfn, buf, csize, offset, userbuf);
> >  }
> >
> > -/*
> > - * Copy to either kernel or user space
> > - */
> > -static int copy_to(void *target, void *src, size_t size, int userbuf)
> > -{
> > -	if (userbuf) {
> > -		if (copy_to_user((char __user *) target, src, size))
> > -			return -EFAULT;
> > -	} else {
> > -		memcpy(target, src, size);
> > -	}
> > -	return 0;
> > -}
> > -
> >  #ifdef CONFIG_PROC_VMCORE_DEVICE_DUMP
> >  static int vmcoredd_copy_dumps(void *dst, u64 start, size_t size, int userbuf)
> >  {
> > diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
> > index ac03940..4a6c3e4 100644
> > --- a/include/linux/uaccess.h
> > +++ b/include/linux/uaccess.h
> > @@ -201,6 +201,20 @@ copy_to_user(void __user *to, const void *from, unsigned long n)
> >  	return n;
> >  }
> >
> > +/*
> > + * Copy to either kernel or user space
> > + */
> > +static inline int copy_to(void *target, void *src, size_t size, int userbuf)
> > +{
> > +	if (userbuf) {
> > +		if (copy_to_user((char __user *) target, src, size))
> > +			return -EFAULT;
> > +	} else {
> > +		memcpy(target, src, size);
> > +	}
> > +	return 0;
> > +}
> > +
>
> Ordinarily I'd say "this is too large to be inlined".  But the function
> has only a single callsite per architecture so inlining it won't cause
> bloat at present.
>
> But hopefully copy_to() will get additional callers in the future, in
> which case it shouldn't be inlined.  So I'm thinking it would be best
> to start out with this as a regular non-inlined function, in
> lib/usercopy.c.
>
> Also, copy_to() is a very poor name for a globally-visible helper
> function.  Better would be copy_to_user_or_kernel(), although that's
> perhaps a bit long.
>
> And the `userbuf' arg should have type bool, yes?

Hi Andrew,

Thank you very much for your reply and suggestion, I agree with you,
I will send v2 later.

Thanks,
Tiezhu