Re: a question about clone_mnt in namespace.c

[yushang <yusunn@gmail.com>]

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@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;
>>   }
>> }
>
> 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.