linux-kernel - Re: [PATCH 17/21] filemap: add FGP_CREAT

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Message-ID: <CAJD7tkapC6es9qjaOf=SmE9XYUdbh_fAperjSe9hy=_iqdB0wQ@mail.gmail.com>
Date: Tue, 27 Feb 2024 18:17:34 -0800
From: Yosry Ahmed <yosryahmed@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Matthew Wilcox <willy@...radead.org>
Cc: Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org, kvm@...r.kernel.org, 
	michael.roth@....com, isaku.yamahata@...el.com, thomas.lendacky@....com
Subject: Re: [PATCH 17/21] filemap: add FGP_CREAT_ONLY

On Tue, Feb 27, 2024 at 6:15 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Tue, Feb 27, 2024, Paolo Bonzini wrote:
>
> This needs a changelog, and also needs to be Cc'd to someone(s) that can give it
> a thumbs up.

+Matthew Wilcox

>
> > Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> > ---
> >  include/linux/pagemap.h | 2 ++
> >  mm/filemap.c            | 4 ++++
> >  2 files changed, 6 insertions(+)
> >
> > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> > index 2df35e65557d..e8ac0b32f84d 100644
> > --- a/include/linux/pagemap.h
> > +++ b/include/linux/pagemap.h
> > @@ -586,6 +586,7 @@ pgoff_t page_cache_prev_miss(struct address_space *mapping,
> >   * * %FGP_CREAT - If no folio is present then a new folio is allocated,
> >   *   added to the page cache and the VM's LRU list.  The folio is
> >   *   returned locked.
> > + * * %FGP_CREAT_ONLY - Fail if a folio is not present
> >   * * %FGP_FOR_MMAP - The caller wants to do its own locking dance if the
> >   *   folio is already in cache.  If the folio was allocated, unlock it
> >   *   before returning so the caller can do the same dance.
> > @@ -606,6 +607,7 @@ typedef unsigned int __bitwise fgf_t;
> >  #define FGP_NOWAIT           ((__force fgf_t)0x00000020)
> >  #define FGP_FOR_MMAP         ((__force fgf_t)0x00000040)
> >  #define FGP_STABLE           ((__force fgf_t)0x00000080)
> > +#define FGP_CREAT_ONLY               ((__force fgf_t)0x00000100)
> >  #define FGF_GET_ORDER(fgf)   (((__force unsigned)fgf) >> 26) /* top 6 bits */
> >
> >  #define FGP_WRITEBEGIN               (FGP_LOCK | FGP_WRITE | FGP_CREAT | FGP_STABLE)
> > diff --git a/mm/filemap.c b/mm/filemap.c
> > index 750e779c23db..d5107bd0cd09 100644
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -1854,6 +1854,10 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
> >               folio = NULL;
> >       if (!folio)
> >               goto no_page;
> > +     if (fgp_flags & FGP_CREAT_ONLY) {
> > +             folio_put(folio);
> > +             return ERR_PTR(-EEXIST);
> > +     }
> >
> >       if (fgp_flags & FGP_LOCK) {
> >               if (fgp_flags & FGP_NOWAIT) {
> > --
> > 2.39.0
> >
> >
>