On 05/31/2012 05:04 PM, Glauber Costa wrote:
> On 05/30/2012 06:58 PM, jeff.liu@xxxxxxxxxx wrote:
>> Introduce two functions to lock/unlock a particular mount namespace
>> when container quota operations is performed.
>>
>> Signed-off-by: Jie Liu<jeff.liu@xxxxxxxxxx>
>> ---
>> fs/namespace.c | 17 +++++++++++++++++
>> include/linux/mnt_namespace.h | 13 +++++++++++++
>> 2 files changed, 30 insertions(+), 0 deletions(-)
>>
>> diff --git a/fs/namespace.c b/fs/namespace.c
>> index e608199..8823ba8 100644
>> --- a/fs/namespace.c
>> +++ b/fs/namespace.c
>> @@ -2633,3 +2633,20 @@ bool our_mnt(struct vfsmount *mnt)
>> {
>> return check_mnt(real_mount(mnt));
>> }
>> +
>> +/*
>> + * Lock the mount namespace when performing a particular container
>> + * disk quotactl operation, especially to protect removing it.
>> + */
>> +void lock_mnt_ns(struct mnt_namespace *ns)
>> +{
>> + down_write(&namespace_sem);
>> +}
>> +
>> +/*
>> + * Unlock the mount namespace after quotactl on that was done.
>> + */
>> +void unlock_mnt_ns(struct mnt_namespace *ns)
>> +{
>> + up_write(&namespace_sem);
>> +}
>> diff --git a/include/linux/mnt_namespace.h
>> b/include/linux/mnt_namespace.h
>> index 5a8e390..ff72ed5 100644
>> --- a/include/linux/mnt_namespace.h
>> +++ b/include/linux/mnt_namespace.h
>> @@ -9,6 +9,19 @@ extern struct mnt_namespace *copy_mnt_ns(unsigned
>> long, struct mnt_namespace *,
>> struct fs_struct *);
>> extern void put_mnt_ns(struct mnt_namespace *ns);
>>
>> +#ifdef CONFIG_NS_QUOTA
>> +extern void lock_mnt_ns(struct mnt_namespace *);
>> +extern void unlock_mnt_ns(struct mnt_namespace *);
>> +#else
>> +void lock_mnt_ns(struct mnt_namespace *)
>> +{
>> +}
>> +
>> +void unlock_mnt_ns(struct mnt_namespace *)
>> +{
>> +}
>> +#endif
>> +
>
> Seems weird. There is nothing ns-quota specific in locking a namespace.
> Also, just grabbing a lock from an outer subsystem is quite ugly. If you
> are grabbing a namespace lock, this suggests you are tweaking namespace
> data. So you should have that file provide you with a function that does
> the full operation.
Maybe this can be safely removed, it is presented like a place holder,
which is suggests to protect changing data inner quota info of a mount
namespace.
However, both quota info initialization and destroy business are all
projected at mount init and put mount namespace stage, so that the
lock/unlock are make less sense here.
Thanks,
-Jeff
>
> Of course there are exceptions to that, but it rings a bell.
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