On Fri, Apr 24, 2020 at 9:26 AM Chengguang Xu <cgxu519@xxxxxxxxxxxx> wrote: > > ---- 在 星期五, 2020-04-24 14:02:00 Amir Goldstein <amir73il@xxxxxxxxx> 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. > I didn't mean we need to check if link_max is valid range for upper fs. We anyway use minimum of user requested value and upper fs max. Frankly, I think there are only two sane options for system wide configuration: 1. disable whiteout link 2. enable whiteout link with ofs->workdir->d_sb->s_max_links So perhaps the module param should be a boolean ovl_whiteout_link_def? Perhaps Kconfig should determine the build time default. Setting whiteout_link smaller than d_sb->s_max_links should be possible via mount option. We may want to support the mount options: whiteout_link_max=<N> whiteout_link_max=auto It should be simple to parse whiteout_link_max=auto, just set config->whiteout_link_max to max uint and let later code reduce it to upper fs max. For ovl_show_options() is slightly more complicated to get right. I am not hooked on any of the ideas above, but I find the current configuration options in v4/v5 not good enough. As an exercise you can try to document those options and see how clear the text is. Thanks, Amir.
