Re: [RFC PATCH v4 6/9] ovl: implement overlayfs' ->write_inode operation

[Chengguang Xu <cgxu519@mykernel.net>]

---- 在 星期五, 2021-04-09 21:49:07 Miklos Szeredi <miklos@szeredi.hu> 撰写 ----
 > On Fri, Nov 13, 2020 at 7:57 AM Chengguang Xu <cgxu519@mykernel.net> wrote:
 > >
 > > Implement overlayfs' ->write_inode to sync dirty data
 > > and redirty overlayfs' inode if necessary.
 > >
 > > Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
 > > ---
 > >  fs/overlayfs/super.c | 30 ++++++++++++++++++++++++++++++
 > >  1 file changed, 30 insertions(+)
 > >
 > > diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
 > > index 883172ac8a12..82e001b97f38 100644
 > > --- a/fs/overlayfs/super.c
 > > +++ b/fs/overlayfs/super.c
 > > @@ -390,6 +390,35 @@ static int ovl_remount(struct super_block *sb, int *flags, char *data)
 > >         return ret;
 > >  }
 > >
 > > +static int ovl_write_inode(struct inode *inode,
 > > +                          struct writeback_control *wbc)
 > > +{
 > > +       struct ovl_fs *ofs = inode->i_sb->s_fs_info;
 > > +       struct inode *upper = ovl_inode_upper(inode);
 > > +       unsigned long iflag = 0;
 > > +       int ret = 0;
 > > +
 > > +       if (!upper)
 > > +               return 0;
 > > +
 > > +       if (!ovl_should_sync(ofs))
 > > +               return 0;
 > > +
 > > +       if (upper->i_sb->s_op->write_inode)
 > > +               ret = upper->i_sb->s_op->write_inode(inode, wbc);
 > > +
 > > +       if (mapping_writably_mapped(upper->i_mapping) ||
 > > +           mapping_tagged(upper->i_mapping, PAGECACHE_TAG_WRITEBACK))
 > > +               iflag |= I_DIRTY_PAGES;
 > > +
 > > +       iflag |= upper->i_state & I_DIRTY_ALL;
 > 
 > How is I_DIRTY_SYNC added/removed from the overlay inode?
 > 

generally, I_DIRTY_SYNC is added to overlay inode when the operation dirties
upper inode, I'll check all those places and call ovl_mark_inode_dirty() to do it.
After writeback if upper inode becomes clean status, we will remove I_DIRTY_SYNC
from overlay inode.

One exception is mmaped file, it will always keep I_DIRTY_SYNC until to be evicted.

Thanks,
Chengguang