Re: [PATCH 05/20] shmem: export shmem_get_folio

[Hugh Dickins <hughd@google.com>]

On Mon, 29 Jan 2024, Christoph Hellwig wrote:

> Export shmem_get_folio as a slightly lower-level variant of
> shmem_read_folio_gfp.  This will be useful for XFS xfile use cases
> that want to pass SGP_NOALLOC or get a locked page, which the thin
> shmem_read_folio_gfp wrapper can't provide.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
> ---
>  mm/shmem.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/mm/shmem.c b/mm/shmem.c
> index ad533b2f0721a7..dae684cd3c99fb 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -2137,12 +2137,27 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
>  	return error;
>  }
>  
> +/**
> + * shmem_get_folio - find and get a reference to a shmem folio.
> + * @inode:	inode to search
> + * @index:	the page index.
> + * @foliop:	pointer to the found folio if one was found
> + * @sgp:	SGP_* flags to control behavior
> + *
> + * Looks up the page cache entry at @inode & @index.
> + *
> + * If this function returns a folio, it is returned with an increased refcount.

If this function returns a folio, it is returned locked, with an increased
refcount.

(Important to mention that it's locked, since that differs from
shmem_read_folio_gfp().)

Hugh

> + *
> + * Return: The found folio, %NULL if SGP_READ or SGP_NOALLOC was passed in @sgp
> + * and no folio was found at @index, or an ERR_PTR() otherwise.
> + */
>  int shmem_get_folio(struct inode *inode, pgoff_t index, struct folio **foliop,
>  		enum sgp_type sgp)
>  {
>  	return shmem_get_folio_gfp(inode, index, foliop, sgp,
>  			mapping_gfp_mask(inode->i_mapping), NULL, NULL);
>  }
> +EXPORT_SYMBOL_GPL(shmem_get_folio);
>  
>  /*
>   * This is like autoremove_wake_function, but it removes the wait queue
> -- 
> 2.39.2