linux-kernel - Re: [PATCHv2 1/9] mm: Introduce new vm_insert_range and vm_insert_range

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Message-ID: <CAFqt6zawBP5Yyy7nfoKz_6ugw8e4MVopvBaeKvaKoXcS-_oSNg@mail.gmail.com>
Date:   Fri, 8 Feb 2019 10:52:16 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Mike Rapoport <rppt@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        vbabka@...e.cz, Rik van Riel <riel@...riel.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        rppt@...ux.vnet.ibm.com, Peter Zijlstra <peterz@...radead.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        robin.murphy@....com, iamjoonsoo.kim@....com, treding@...dia.com,
        Kees Cook <keescook@...omium.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        stefanr@...6.in-berlin.de, hjc@...k-chips.com,
        Heiko Stuebner <heiko@...ech.de>, airlied@...ux.ie,
        oleksandr_andrushchenko@...m.com, joro@...tes.org,
        pawel@...iak.com, Kyungmin Park <kyungmin.park@...sung.com>,
        mchehab@...nel.org, Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
        Linux-MM <linux-mm@...ck.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux1394-devel@...ts.sourceforge.net,
        dri-devel@...ts.freedesktop.org,
        linux-rockchip@...ts.infradead.org, xen-devel@...ts.xen.org,
        iommu@...ts.linux-foundation.org, linux-media@...r.kernel.org
Subject: Re: [PATCHv2 1/9] mm: Introduce new vm_insert_range and
 vm_insert_range_buggy API

On Thu, Feb 7, 2019 at 10:17 PM Matthew Wilcox <willy@...radead.org> 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 ) ?