Re: [PATCH v4] ovl: whiteout inode sharing

[Chengguang Xu <cgxu519@mykernel.net>]

 ---- 在 星期五, 2020-04-24 14:02:00 Amir Goldstein <amir73il@gmail.com> 撰写 ----
 > >  > > +               case OPT_WHITEOUT_LINK_MAX:
 > >  > > +                       if (match_int(&args[0], &link_max))
 > >  > > +                               return -EINVAL;
 > >  > > +                       if (link_max < ovl_whiteout_link_max_def)
 > >  > > +                               config->whiteout_link_max = link_max;
 > >  >
 > >  > Why not allow link_max > ovl_whiteout_link_max_def?
 > >  > admin may want to disable ovl_whiteout_link_max_def by default
 > >  > in module parameter, but allow it for specific overlay instances.
 > >  >
 > >
 > > In this use case, seems we don't need module param any more, we just need to set  default value for option.
 > >
 > > I would like to treate module param as a total switch, so that it could disable the feathre for all instances at the same time.
 > > I think sometimes it's helpful for lazy admin(like me).
 > >
 > 
 > I am not convinced.
 > 
 > lazy admin could very well want to disable whiteout_link_max by default,
 > but allow user to specify whiteout_link_max for a specific mount.
 > 
 > In fact, in order to preserve existing behavior and not cause regression with
 > some special filesystems, distros could decide that default disabled is
 > a reasonable choice.
 > 
 > I don't understand at all what the purpose of this limitation is.
 > 

If user sets a ridiculous  link_max which is larger than valid range of upper fs, I think it is hard to verify in the stage of option parsing.
So I hope to fix the upper limit using module parameter, we can set default mount option to  0/1 for the use case you mentioned above.


Thanks,
cgxu