Re: [PATCH v2 06/11] md/md-bitmap: delay registration of bitmap_ops until creating bitmap

[余快 <yukuai1994@gmail.com>]

Hi,

在 2025/7/8 19:57, Hannes Reinecke 写道:
> On 7/8/25 13:31, 余快 wrote:
>> Hi,
>>
>> Hannes Reinecke <hare@suse.de <mailto:hare@suse.de>> 于2025年7月8日周二
>> 14:29写道：
>>
>>      > +     if (mddev->bitmap_ops->group && !mddev_is_dm(mddev)) {
>>      > +             if (sysfs_create_group(&mddev->kobj, mddev-
>>      >bitmap_ops->group))
>>      > +                     pr_warn("md: cannot register extra bitmap
>>     attributes for %s\n",
>>      > +                             mdname(mddev));
>>      > +             else
>>      > +  kobject_uevent(&mddev->kobj, KOBJ_CHANGE);
>>      > +     }
>>      >       return true;
>>      >
>>      >   err:
>>
>>     Ouch. This will cause havoc with the udev rules.
>>     Having different events for 'add' and 'change' tends to confuse udev
>>     rules (most treat 'add' and 'change' identically), so at the very
>> least
>>     you would need to document this.
>>
>>
>> Do you mean document here as new sysfs entries are created under mddev
>> kobject?
>>
> No, I meant to document that 'add' events will have access to
> different sysfs attributes than the 'change' events.
> In the running system one will only see the final status, so it's not
> immediately obvious that some attributes are only valid for 'change',
> and not for 'add'.

Thanks for the explanation, just to make sure you mean:

diff --git a/Documentation/admin-guide/md.rst
b/Documentation/admin-guide/md.rst
index 2030772075b5..db7a39894c8d 100644
--- a/Documentation/admin-guide/md.rst
+++ b/Documentation/admin-guide/md.rst
@@ -388,6 +388,9 @@ All md devices contain:
       bitmap
           The default internal bitmap

+If bitmap_type is not none, then additional bitmap attributes will be
created
+after md device KOBJ_CHANGE event.
+
  If bitmap_type is bitmap, then the md device will also contain:

    bitmap/location
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 22378686a964..60e2de23c9b5 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -699,6 +699,7 @@ static bool mddev_set_bitmap_ops(struct mddev *mddev)
                         pr_warn("md: cannot register extra bitmap
attributes for %s\n",
                                 mdname(mddev));
                 else
+                       /* Inform user with KOBJ_CHANGE about new bitmap
attributes. */
                         kobject_uevent(&mddev->kobj, KOBJ_CHANGE);
         }
         return true;

>
> Cheers,
>
> Hannes