Re: [RFC PATCH v3 07/10] ovl: implement overlayfs' ->write_inode operation

[Chengguang Xu <cgxu519@mykernel.net>]

 ---- 在 星期二, 2020-11-10 21:45:51 Jan Kara <jack@suse.cz> 撰写 ----
 > On Sun 08-11-20 22:03:04, Chengguang Xu wrote:
 > > +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);
 > > +
 > > +    iflag |= upper->i_state & I_DIRTY_ALL;
 > > +
 > > +    if (mapping_writably_mapped(upper->i_mapping) ||
 > > +        mapping_tagged(upper->i_mapping, PAGECACHE_TAG_WRITEBACK))
 > > +        iflag |= I_DIRTY_PAGES;
 > > +
 > > +    if (iflag)
 > > +        ovl_mark_inode_dirty(inode);
 > 
 > I think you didn't incorporate feedback we were speaking about in the last
 > version of the series. May comment in [1] still applies - you can miss
 > inodes dirtied through mmap when you decide to clean the inode here. So
 > IMHO you need something like:
 > 
 >     if (inode_is_open_for_write(inode))
 >         ovl_mark_inode_dirty(inode);
 > 
 > here to keep inode dirty while it is open for write (and not based on upper
 > inode state which is unreliable).

Hi Jan,

I not only checked upper inode state but also checked upper inode mmap(shared) state
using  mapping_writably_mapped(upper->i_mapping). Maybe it's better to move i_state check
after mmap check but isn't above checks enough for mmapped file? 

Below code is the definition of mmapping_writably_mapped(), I think it will check shared mmap
regardless write or read permission though the function name is quite confusable.

static inline int mapping_writably_mapped(struct address_space *mapping)
{
	return atomic_read(&mapping->i_mmap_writable) > 0;
}



Thanks,
Chengguang


 > 
 >                                 Honza
 > 
 > [1] https://lore.kernel.org/linux-fsdevel/20201105140332.GG32718@quack2.suse.cz/
 > 
 > > +
 > > +    return ret;
 > > +}
 > > +
 > >  static void ovl_evict_inode(struct inode *inode)
 > >  {
 > >      struct ovl_fs *ofs = inode->i_sb->s_fs_info;
 > > @@ -411,6 +440,7 @@ static const struct super_operations ovl_super_operations = {
 > >      .destroy_inode    = ovl_destroy_inode,
 > >      .drop_inode    = generic_delete_inode,
 > >      .evict_inode    = ovl_evict_inode,
 > > +    .write_inode    = ovl_write_inode,
 > >      .put_super    = ovl_put_super,
 > >      .sync_fs    = ovl_sync_fs,
 > >      .statfs        = ovl_statfs,
 > > -- 
 > > 2.26.2
 > > 
 > > 
 > -- 
 > Jan Kara <jack@suse.com>
 > SUSE Labs, CR
 >