Re: [RFC PATCH v3 06/10] ovl: mark overlayfs' inode dirty on shared mmap

[Amir Goldstein <amir73il@gmail.com>]

On Wed, Nov 11, 2020 at 3:05 PM Chengguang Xu <cgxu519@mykernel.net> wrote:
>
>  ---- 在 星期日, 2020-11-08 22:03:03 Chengguang Xu <cgxu519@mykernel.net> 撰写 ----
>  > Overlayfs cannot be notified when mmapped area gets dirty,
>  > so we need to proactively mark inode dirty in ->mmap operation.
>  >
>  > Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
>  > ---
>  >  fs/overlayfs/file.c | 2 ++
>  >  1 file changed, 2 insertions(+)
>  >
>  > diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
>  > index efccb7c1f9bc..662252047fff 100644
>  > --- a/fs/overlayfs/file.c
>  > +++ b/fs/overlayfs/file.c
>  > @@ -486,6 +486,8 @@ static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
>  >          /* Drop reference count from new vm_file value */
>  >          fput(realfile);
>  >      } else {
>  > +        if (vma->vm_flags & (VM_SHARED|VM_MAYSHARE))
>
> Maybe it's better to mark dirty only having upper inode.
>

Yeh.

And since mapping_map_writable() is only called if VM_SHARED flag
is set (and not VM_MAYSHARE), we are not going to re-dirty an inode on
account of VM_MAYSHARE alone, so I wonder why we need to mark it
dirty here on account of VM_MAYSHARE?

Thanks,
Amir.