Re: [PATCH 07/10] mm/filemap: introduce generic_file_*_mmap_prepare() helpers

[Vlastimil Babka]

On 6/16/25 21:33, Lorenzo Stoakes wrote:
> Since commit c84bf6dd2b83 ("mm: introduce new .mmap_prepare() file
> callback"), the f_op->mmap() hook has been deprecated in favour of
> f_op->mmap_prepare().
> 
> The generic mmap handlers are very simple, so we can very easily convert
> these in advance of converting file systems which use them.
> 
> This patch does so.
> 
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

> ---
>  include/linux/fs.h |  6 ++++--
>  mm/filemap.c       | 29 +++++++++++++++++++++++++++++
>  2 files changed, 33 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 7120f80255b3..65cffc445fcc 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3395,8 +3395,10 @@ extern void inode_add_lru(struct inode *inode);
>  extern int sb_set_blocksize(struct super_block *, int);
>  extern int sb_min_blocksize(struct super_block *, int);
>  
> -extern int generic_file_mmap(struct file *, struct vm_area_struct *);
> -extern int generic_file_readonly_mmap(struct file *, struct vm_area_struct *);
> +int generic_file_mmap(struct file *, struct vm_area_struct *);
> +int generic_file_mmap_prepare(struct vm_area_desc *desc);
> +int generic_file_readonly_mmap(struct file *, struct vm_area_struct *);
> +int generic_file_readonly_mmap_prepare(struct vm_area_desc *desc);
>  extern ssize_t generic_write_checks(struct kiocb *, struct iov_iter *);
>  int generic_write_checks_count(struct kiocb *iocb, loff_t *count);
>  extern int generic_write_check_limits(struct file *file, loff_t pos,
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 93fbc2ef232a..e75608cbf420 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -3847,6 +3847,18 @@ int generic_file_mmap(struct file *file, struct vm_area_struct *vma)
>  	return 0;
>  }
>  
> +int generic_file_mmap_prepare(struct vm_area_desc *desc)
> +{
> +	struct file *file = desc->file;
> +	struct address_space *mapping = file->f_mapping;
> +
> +	if (!mapping->a_ops->read_folio)
> +		return -ENOEXEC;
> +	file_accessed(file);
> +	desc->vm_ops = &generic_file_vm_ops;
> +	return 0;
> +}
> +
>  /*
>   * This is for filesystems which do not implement ->writepage.
>   */
> @@ -3856,6 +3868,13 @@ int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
>  		return -EINVAL;
>  	return generic_file_mmap(file, vma);
>  }
> +
> +int generic_file_readonly_mmap_prepare(struct vm_area_desc *desc)
> +{
> +	if (is_shared_maywrite(desc->vm_flags))
> +		return -EINVAL;
> +	return generic_file_mmap_prepare(desc);
> +}
>  #else
>  vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf)
>  {
> @@ -3865,15 +3884,25 @@ int generic_file_mmap(struct file *file, struct vm_area_struct *vma)
>  {
>  	return -ENOSYS;
>  }
> +int generic_file_mmap_prepare(struct vm_area_desc *desc)
> +{
> +	return -ENOSYS;
> +}
>  int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
>  {
>  	return -ENOSYS;
>  }
> +int generic_file_readonly_mmap_prepare(struct vm_area_desc *desc)
> +{
> +	return -ENOSYS;
> +}
>  #endif /* CONFIG_MMU */
>  
>  EXPORT_SYMBOL(filemap_page_mkwrite);
>  EXPORT_SYMBOL(generic_file_mmap);
> +EXPORT_SYMBOL(generic_file_mmap_prepare);
>  EXPORT_SYMBOL(generic_file_readonly_mmap);
> +EXPORT_SYMBOL(generic_file_readonly_mmap_prepare);
>  
>  static struct folio *do_read_cache_folio(struct address_space *mapping,
>  		pgoff_t index, filler_t filler, struct file *file, gfp_t gfp)