Re: [PATCHv2 1/9] mm: Introduce new vm_insert_range and vm_insert_range_buggy API

[Souptick Joarder]

On Thu, Feb 7, 2019 at 10:17 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> On Thu, Feb 07, 2019 at 09:19:47PM +0530, Souptick Joarder wrote:
> > Just thought to take opinion for documentation before placing it in v3.
> > Does it looks fine ?
> >
> > +/**
> > + * __vm_insert_range - insert range of kernel pages into user vma
> > + * @vma: user vma to map to
> > + * @pages: pointer to array of source kernel pages
> > + * @num: number of pages in page array
> > + * @offset: user's requested vm_pgoff
> > + *
> > + * This allow drivers to insert range of kernel pages into a user vma.
> > + *
> > + * Return: 0 on success and error code otherwise.
> > + */
> > +static int __vm_insert_range(struct vm_area_struct *vma, struct page **pages,
> > +                               unsigned long num, unsigned long offset)
>
> For static functions, I prefer to leave off the second '*', ie make it
> formatted like a docbook comment, but not be processed like a docbook
> comment.  That avoids cluttering the html with descriptions of internal
> functions that people can't actually call.
>
> > +/**
> > + * vm_insert_range - insert range of kernel pages starts with non zero offset
> > + * @vma: user vma to map to
> > + * @pages: pointer to array of source kernel pages
> > + * @num: number of pages in page array
> > + *
> > + * Maps an object consisting of `num' `pages', catering for the user's
>
> Rather than using `num', you should use @num.
>
> > + * requested vm_pgoff
> > + *
> > + * If we fail to insert any page into the vma, the function will return
> > + * immediately leaving any previously inserted pages present.  Callers
> > + * from the mmap handler may immediately return the error as their caller
> > + * will destroy the vma, removing any successfully inserted pages. Other
> > + * callers should make their own arrangements for calling unmap_region().
> > + *
> > + * Context: Process context. Called by mmap handlers.
> > + * Return: 0 on success and error code otherwise.
> > + */
> > +int vm_insert_range(struct vm_area_struct *vma, struct page **pages,
> > +                               unsigned long num)
> >
> >
> > +/**
> > + * vm_insert_range_buggy - insert range of kernel pages starts with zero offset
> > + * @vma: user vma to map to
> > + * @pages: pointer to array of source kernel pages
> > + * @num: number of pages in page array
> > + *
> > + * Similar to vm_insert_range(), except that it explicitly sets @vm_pgoff to
>
> But vm_pgoff isn't a parameter, so it's misleading to format it as such.
>
> > + * 0. This function is intended for the drivers that did not consider
> > + * @vm_pgoff.
> > + *
> > + * Context: Process context. Called by mmap handlers.
> > + * Return: 0 on success and error code otherwise.
> > + */
> > +int vm_insert_range_buggy(struct vm_area_struct *vma, struct page **pages,
> > +                               unsigned long num)
>
> I don't think we should call it 'buggy'.  'zero' would make more sense
> as a suffix.

suffix can be *zero or zero_offset* whichever suits better.

>
> Given how this interface has evolved, I'm no longer sure than
> 'vm_insert_range' makes sense as the name for it.  Is it perhaps
> 'vm_map_object' or 'vm_map_pages'?
>

I prefer vm_map_pages. Considering it, both the interface name can be changed
to *vm_insert_range -> vm_map_pages* and *vm_insert_range_buggy ->
vm_map_pages_{zero/zero_offset}.

As this is only change in interface name and rest of code remain same
shall I post it in v3 ( with additional change log mentioned about interface
name changed) ?

or,

It will be a new patch series ( with carry forward all the Reviewed-by
/ Tested-by on
vm_insert_range/ vm_insert_range_buggy ) ?