linux-kernel - Re: [PATCH v7 3/8] fsdax: Replace mmap entry in case of CoW

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Date:   Thu, 26 Aug 2021 22:00:23 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Shiyang Ruan <ruansy.fnst@...itsu.com>
Cc:     Christoph Hellwig <hch@....de>,
        "Darrick J. Wong" <djwong@...nel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        david <david@...morbit.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux NVDIMM <nvdimm@...ts.linux.dev>,
        Goldwyn Rodrigues <rgoldwyn@...e.de>,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>,
        Goldwyn Rodrigues <rgoldwyn@...e.com>,
        Ritesh Harjani <riteshh@...ux.ibm.com>
Subject: Re: [PATCH v7 3/8] fsdax: Replace mmap entry in case of CoW

On Thu, Aug 26, 2021 at 8:22 PM Shiyang Ruan <ruansy.fnst@...itsu.com> wrote:
>
>
>
> On 2021/8/23 20:57, Christoph Hellwig wrote:
> > On Thu, Aug 19, 2021 at 03:54:01PM -0700, Dan Williams wrote:
> >>
> >> static void *dax_insert_entry(struct xa_state *xas, struct vm_fault *vmf,
> >>                                const struct iomap_iter *iter, void
> >> *entry, pfn_t pfn,
> >>                                unsigned long flags)
> >>
> >>
> >>>   {
> >>> +       struct address_space *mapping = vmf->vma->vm_file->f_mapping;
> >>>          void *new_entry = dax_make_entry(pfn, flags);
> >>> +       bool dirty = insert_flags & DAX_IF_DIRTY;
> >>> +       bool cow = insert_flags & DAX_IF_COW;
> >>
> >> ...and then calculate these flags from the source data. I'm just
> >> reacting to "yet more flags".
> >
> > Except for the overly long line above that seems like a good idea.
> > The iomap_iter didn't exist for most of the time this patch has been
> > around.
> >
>
> So should I reuse the iter->flags to pass the insert_flags? (left shift
> it to higher bits)

No, the advice is to just pass the @iter to dax_insert_entry directly
and calculate @dirty and @cow internally.