On 03.12.20 15:59, Jan Beulich wrote:
> On 01.12.2020 09:21, Juergen Gross wrote:
>> In order to better support resource allocation and locking for dynamic
>> hypfs nodes add enter() and exit() callbacks to struct hypfs_funcs.
>>
>> The enter() callback is called when entering a node during hypfs user
>> actions (traversing, reading or writing it), while the exit() callback
>> is called when leaving a node (accessing another node at the same or a
>> higher directory level, or when returning to the user).
>>
>> For avoiding recursion this requires a parent pointer in each node.
>> Let the enter() callback return the entry address which is stored as
>> the last accessed node in order to be able to use a template entry for
>> that purpose in case of dynamic entries.
> 
> I guess I'll learn in subsequent patches why this is necessary /
> useful. Right now it looks odd for the function to simple return
> the incoming argument, as this way it's clear the caller knows
> the correct value already.

Basically for dynamic entries based on a template the entry function
will return the address of template->e instead of the dynamic entry
itself. This will enable to have the standard entry functions for
any nodes being linked to the template.

> 
>> @@ -100,11 +112,58 @@ static void hypfs_unlock(void)
>>       }
>>   }
>>   
>> +const struct hypfs_entry *hypfs_node_enter(const struct hypfs_entry *entry)
>> +{
>> +    return entry;
>> +}
>> +
>> +void hypfs_node_exit(const struct hypfs_entry *entry)
>> +{
>> +}
>> +
>> +static int node_enter(const struct hypfs_entry *entry)
>> +{
>> +    const struct hypfs_entry **last = &this_cpu(hypfs_last_node_entered);
>> +
>> +    entry = entry->funcs->enter(entry);
>> +    if ( IS_ERR(entry) )
>> +        return PTR_ERR(entry);
>> +
>> +    ASSERT(!*last || *last == entry->parent);
>> +
>> +    *last = entry;
>> +
>> +    return 0;
>> +}
>> +
>> +static void node_exit(const struct hypfs_entry *entry)
>> +{
>> +    const struct hypfs_entry **last = &this_cpu(hypfs_last_node_entered);
>> +
>> +    if ( !*last )
>> +        return;
> 
> Under what conditions is this legitimate to happen? IOW shouldn't
> there be an ASSERT_UNREACHABLE() here?

This is for the "/" node.


Juergen