Re: [PATCH 6/8] ntb_tool: Add link status file to debugfs

[Allen Hubbe]

On Sat, Jun 11, 2016 at 11:28 AM, Logan Gunthorpe <logang@xxxxxxxxxxxx> wrote:
> Hey Allen,
>
> Thanks for the feedback it's a bit more complicated but I don't object to
> that. I'll work something up on Monday.
>
> I was trying to avoid adding link controls, but if we do, would you say the
> module should still enable the link when it's installed? Or would we have
> the user explicitly have to enable the link before using it?

I would vote to keep the current behavior and enable the link when the
module loads.

>
> Thanks,
>
> Logan
>
>
> On 10/06/16 08:27 PM, Allen Hubbe wrote:
>>
>> On Fri, Jun 10, 2016 at 6:54 PM, Logan Gunthorpe <logang@xxxxxxxxxxxx>
>> wrote:
>>>
>>> In order to more successfully script with ntb_tool it's useful to
>>> have a link file to check the link status so that the script
>>> doesn't use the other files until the link is up.
>>>
>>> This commit adds a 'link' file to the debugfs directory which reads
>>> 0 or 1 depending on the link status. For scripting convenience, writing
>>> will block until the link is up (discarding anything that was written).
>>>
>>> Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
>>> ---
>>>   drivers/ntb/test/ntb_tool.c | 45
>>> +++++++++++++++++++++++++++++++++++++++++++++
>>>   1 file changed, 45 insertions(+)
>>>
>>> diff --git a/drivers/ntb/test/ntb_tool.c b/drivers/ntb/test/ntb_tool.c
>>> index 954e1d5..116352e 100644
>>> --- a/drivers/ntb/test/ntb_tool.c
>>> +++ b/drivers/ntb/test/ntb_tool.c
>>> @@ -59,6 +59,12 @@
>>>    *
>>>    * Eg: check if clearing the doorbell mask generates an interrupt.
>>>    *
>>> + * # Check the link status
>>> + * root@self# cat $DBG_DIR/link
>>> + *
>>> + * # Block until the link is up
>>> + * root@self# echo > $DBG_DIR/link
>>
>>
>> I think a file to get and set the link status is a good idea, but the
>> way it is done as proposed here is not in a similar style to other
>> ntb_tool operations.  Other operations simply read a register and
>> format the value, or scan a value and write a register.  Similarly, I
>> think the link status could be done in the same way: use the read file
>> operation to get the current status with ntb_link_is_up(), and use the
>> file write operation to enable or disable the link with
>> ntb_link_enable() and ntb_link_disable().
>>
>> Waiting for link status is an interesting concept, too.  Really, one
>> might be interested in a change in link status, whether up or down.
>> What about a link event file that supports write to arm the event, and
>> read to block for the event.  Consider an implementation based on
>> <linux/completion.h>.  It would be used in combination with the link
>> status file, above, as follows.
>>
>> 1: Write 1 to the event file.  This arms the event.
>>    - The event will be disarmed by the next tool_link_event().
>>
>> 2: The application may read the link status file if it is interested
>> in waiting for a particular event.
>>
>> 3. The application may wait for an event by reading the event file
>>    - The application will wait as long as the event is still armed.
>>    - If the event was disarmed before waiting, the application will not
>> block.
>>
>> 4. The application should read the link status again.
>>
>> In any case, I think it would be more expected and natural to block
>> while reading a file versus writing it.
>>
>>> + *
>>>    * # Set the doorbell mask
>>>    * root@self# echo 's 1' > $DBG_DIR/mask
>>>    *
>>> @@ -127,6 +133,7 @@ struct tool_ctx {
>>>          struct work_struct link_cleanup;
>>>          bool link_is_up;
>>>          struct delayed_work link_work;
>>> +       wait_queue_head_t link_wq;
>>>          int mw_count;
>>>          struct tool_mw mws[MAX_MWS];
>>>   };
>>> @@ -237,6 +244,7 @@ static void tool_link_work(struct work_struct *work)
>>>                          "Error setting up memory windows: %d\n", rc);
>>>
>>>          tc->link_is_up = true;
>>> +       wake_up(&tc->link_wq);
>>>   }
>>>
>>>   static void tool_link_cleanup(struct work_struct *work)
>>> @@ -573,6 +581,39 @@ static TOOL_FOPS_RDWR(tool_peer_spad_fops,
>>>                        tool_peer_spad_read,
>>>                        tool_peer_spad_write);
>>>
>>> +static ssize_t tool_link_read(struct file *filep, char __user *ubuf,
>>> +                             size_t size, loff_t *offp)
>>> +{
>>> +       struct tool_ctx *tc = filep->private_data;
>>> +       char *buf;
>>> +       ssize_t pos, rc;
>>> +
>>> +       buf = kmalloc(64, GFP_KERNEL);
>>> +       if (!buf)
>>> +               return -ENOMEM;
>>> +
>>> +       pos = scnprintf(buf, 64, "%d\n", tc->link_is_up);
>>> +       rc = simple_read_from_buffer(ubuf, size, offp, buf, pos);
>>> +
>>> +       kfree(buf);
>>> +
>>> +       return rc;
>>> +}
>>> +
>>> +static ssize_t tool_link_write(struct file *filep, const char __user
>>> *ubuf,
>>> +                              size_t size, loff_t *offp)
>>> +{
>>> +       struct tool_ctx *tc = filep->private_data;
>>> +
>>> +       if (wait_event_interruptible(tc->link_wq, tc->link_is_up))
>>> +               return -ERESTART;
>>> +
>>> +       return size;
>>> +}
>>> +
>>> +static TOOL_FOPS_RDWR(tool_link_fops,
>>> +                     tool_link_read,
>>> +                     tool_link_write);
>>>
>>>   static ssize_t tool_mw_read(struct file *filep, char __user *ubuf,
>>>                              size_t size, loff_t *offp)
>>> @@ -708,6 +749,9 @@ static void tool_setup_dbgfs(struct tool_ctx *tc)
>>>          debugfs_create_file("peer_spad", S_IRUSR | S_IWUSR, tc->dbgfs,
>>>                              tc, &tool_peer_spad_fops);
>>>
>>> +       debugfs_create_file("link", S_IRUSR | S_IWUSR, tc->dbgfs,
>>> +                           tc, &tool_link_fops);
>>> +
>>>          mw_count = min(ntb_mw_count(tc->ntb), MAX_MWS);
>>>          for (i = 0; i < mw_count; i++) {
>>>                  char buf[30];
>>> @@ -741,6 +785,7 @@ static int tool_probe(struct ntb_client *self, struct
>>> ntb_dev *ntb)
>>>          }
>>>
>>>          tc->ntb = ntb;
>>> +       init_waitqueue_head(&tc->link_wq);
>>>          INIT_DELAYED_WORK(&tc->link_work, tool_link_work);
>>>          INIT_WORK(&tc->link_cleanup, tool_link_cleanup);