Re: [PATCH 10/13] mm: Wire up MAP_SYNC

[Christoph Hellwig <hch@infradead.org>]

On Thu, Aug 17, 2017 at 06:08:12PM +0200, Jan Kara wrote:
> Pretty crude for now...
> 
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
>  fs/ext4/file.c                  | 2 ++
>  include/linux/mm.h              | 1 +
>  include/linux/mman.h            | 3 ++-
>  include/uapi/asm-generic/mman.h | 1 +
>  mm/mmap.c                       | 5 +++++
>  5 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index f84bb29e941e..850037e140d7 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -340,6 +340,8 @@ static int ext4_file_mmap(struct file *file, struct vm_area_struct *vma)
>  		vma->vm_flags |= VM_MIXEDMAP | VM_HUGEPAGE;
>  	} else {
>  		vma->vm_ops = &ext4_file_vm_ops;
> +		if (vma->vm_flags & VM_SYNC)
> +			return -EOPNOTSUPP;
>  	}

So each mmap instance would need to reject the flag explicitly?

Or do I misunderstand this VM_SYNC flag?