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yushang | 20 Jun 2012 04:54
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a question about clone_mnt in namespace.c

Hi dear all,
I have a question about the mnt_master logic in clone_mnt , look at
following lines:
...
} else if (!(flag & CL_PRIVATE)) {
  if ((flag & CL_MAKE_SHARED) || IS_MNT_SHARED(old))
	list_add(&mnt->mnt_share, &old->mnt_share);
  if (IS_MNT_SLAVE(old))
	list_add(&mnt->mnt_slave, &old->mnt_slave);
    mnt->mnt_master = old->mnt_master;
}
...
I think the following lines are equivalent, right ? or I've missed
something ? many thanks!
...
} else if (!(flag & CL_PRIVATE)) {
  if ((flag & CL_MAKE_SHARED) || IS_MNT_SHARED(old))
	list_add(&mnt->mnt_share, &old->mnt_share);
  if (IS_MNT_SLAVE(old)) {
	list_add(&mnt->mnt_slave, &old->mnt_slave);
        mnt->mnt_master = old->mnt_master;
  }
}
...
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Al Viro | 22 Jun 2012 11:29
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Re: a question about clone_mnt in namespace.c

On Wed, Jun 20, 2012 at 10:54:00AM +0800, yushang wrote:
> Hi dear all,
> I have a question about the mnt_master logic in clone_mnt , look at
> following lines:
> ...
> } else if (!(flag & CL_PRIVATE)) {
>   if ((flag & CL_MAKE_SHARED) || IS_MNT_SHARED(old))
> 	list_add(&mnt->mnt_share, &old->mnt_share);
>   if (IS_MNT_SLAVE(old))
> 	list_add(&mnt->mnt_slave, &old->mnt_slave);
>     mnt->mnt_master = old->mnt_master;
> }
> ...
> I think the following lines are equivalent, right ? or I've missed
> something ? many thanks!
> ...
> } else if (!(flag & CL_PRIVATE)) {
>   if ((flag & CL_MAKE_SHARED) || IS_MNT_SHARED(old))
> 	list_add(&mnt->mnt_share, &old->mnt_share);
>   if (IS_MNT_SLAVE(old)) {
> 	list_add(&mnt->mnt_slave, &old->mnt_slave);
>         mnt->mnt_master = old->mnt_master;
>   }
> }

Yes; we are guaranteed that mnt->master is NULL after alloc_vfsmnt(),
so that would be an equivalent transformation.  Matter of taste,
mostly - performance win is negligible and IMO your variant is
slightly less explicit.
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yushang | 1 Jul 2012 04:03
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Re: a question about clone_mnt in namespace.c

Thanks for reply. I think mnt_slave and mnt_master are integrity parts
of master/slave semantics and put the 2 lines together will make the
logic clearer.
Many thanks.

2012/6/22 Al Viro <viro <at> zeniv.linux.org.uk>:
> On Wed, Jun 20, 2012 at 10:54:00AM +0800, yushang wrote:
>> Hi dear all,
>> I have a question about the mnt_master logic in clone_mnt , look at
>> following lines:
>> ...
>> } else if (!(flag & CL_PRIVATE)) {
>>   if ((flag & CL_MAKE_SHARED) || IS_MNT_SHARED(old))
>>       list_add(&mnt->mnt_share, &old->mnt_share);
>>   if (IS_MNT_SLAVE(old))
>>       list_add(&mnt->mnt_slave, &old->mnt_slave);
>>     mnt->mnt_master = old->mnt_master;
>> }
>> ...
>> I think the following lines are equivalent, right ? or I've missed
>> something ? many thanks!
>> ...
>> } else if (!(flag & CL_PRIVATE)) {
>>   if ((flag & CL_MAKE_SHARED) || IS_MNT_SHARED(old))
>>       list_add(&mnt->mnt_share, &old->mnt_share);
>>   if (IS_MNT_SLAVE(old)) {
>>       list_add(&mnt->mnt_slave, &old->mnt_slave);
>>         mnt->mnt_master = old->mnt_master;
>>   }
>> }
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