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.
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> 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
>
>
