Re: [PATCH v3 3/8] xen/hypfs: add new enter() and exit() per node callbacks

[Jan Beulich <jbeulich@xxxxxxxx>]

On 16.12.2020 17:24, Jürgen Groß wrote:
> On 16.12.20 17:16, Jan Beulich wrote:
>> On 09.12.2020 17:09, 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.
>>>
>>> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
>>> ---
>>> V2:
>>> - new patch
>>>
>>> V3:
>>> - add ASSERT(entry); (Jan Beulich)
>>>
>>> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
>>> ---
>>>   xen/common/hypfs.c      | 80 +++++++++++++++++++++++++++++++++++++++++
>>>   xen/include/xen/hypfs.h |  5 +++
>>>   2 files changed, 85 insertions(+)
>>>
>>> diff --git a/xen/common/hypfs.c b/xen/common/hypfs.c
>>> index 6f822ae097..f04934db10 100644
>>> --- a/xen/common/hypfs.c
>>> +++ b/xen/common/hypfs.c
>>> @@ -25,30 +25,40 @@ CHECK_hypfs_dirlistentry;
>>>        ROUNDUP((name_len) + 1, alignof(struct xen_hypfs_direntry)))
>>>   
>>>   const struct hypfs_funcs hypfs_dir_funcs = {
>>> +    .enter = hypfs_node_enter,
>>> +    .exit = hypfs_node_exit,
>>>       .read = hypfs_read_dir,
>>>       .write = hypfs_write_deny,
>>>       .getsize = hypfs_getsize,
>>>       .findentry = hypfs_dir_findentry,
>>>   };
>>>   const struct hypfs_funcs hypfs_leaf_ro_funcs = {
>>> +    .enter = hypfs_node_enter,
>>> +    .exit = hypfs_node_exit,
>>>       .read = hypfs_read_leaf,
>>>       .write = hypfs_write_deny,
>>>       .getsize = hypfs_getsize,
>>>       .findentry = hypfs_leaf_findentry,
>>>   };
>>>   const struct hypfs_funcs hypfs_leaf_wr_funcs = {
>>> +    .enter = hypfs_node_enter,
>>> +    .exit = hypfs_node_exit,
>>>       .read = hypfs_read_leaf,
>>>       .write = hypfs_write_leaf,
>>>       .getsize = hypfs_getsize,
>>>       .findentry = hypfs_leaf_findentry,
>>>   };
>>>   const struct hypfs_funcs hypfs_bool_wr_funcs = {
>>> +    .enter = hypfs_node_enter,
>>> +    .exit = hypfs_node_exit,
>>>       .read = hypfs_read_leaf,
>>>       .write = hypfs_write_bool,
>>>       .getsize = hypfs_getsize,
>>>       .findentry = hypfs_leaf_findentry,
>>>   };
>>>   const struct hypfs_funcs hypfs_custom_wr_funcs = {
>>> +    .enter = hypfs_node_enter,
>>> +    .exit = hypfs_node_exit,
>>>       .read = hypfs_read_leaf,
>>>       .write = hypfs_write_custom,
>>>       .getsize = hypfs_getsize,
>>> @@ -63,6 +73,8 @@ enum hypfs_lock_state {
>>>   };
>>>   static DEFINE_PER_CPU(enum hypfs_lock_state, hypfs_locked);
>>>   
>>> +static DEFINE_PER_CPU(const struct hypfs_entry *, hypfs_last_node_entered);
>>> +
>>>   HYPFS_DIR_INIT(hypfs_root, "");
>>>   
>>>   static void hypfs_read_lock(void)
>>> @@ -100,11 +112,59 @@ 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(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;
>>
>> To my question regarding this in v2 you replied
>>
>> "I rechecked and have found that this was a remnant from an earlier
>>   variant. *last won't ever be NULL, so the if can be dropped (a NULL
>>   will be catched by the following ASSERT())."
>>
>> Now this if() is still there. Why?
> 
> I really thought I did remove the if(). Seems as if I did that on
> my test machine only and not in my git tree. Sorry for that.

So should I drop it while committing and adding
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
?

Jan