[PATCH V6 1/5] drm: add drm_file_err function to add process info

[Khatri, Sunil]

On 4/17/2025 7:04 PM, Tvrtko Ursulin wrote:
>
> On 17/04/2025 13:31, Sunil Khatri wrote:
>> Add a drm helper function which append the process information for
>
> appends
Noted
>
>> the drm_file over drm_err formated output.
>
> formatted
'Noted
>
>> v5: change to macro from function (Christian Koenig)
>>      add helper functions for lock/unlock (Christian Koenig)
>>
>> v6: remove __maybe_unused and make function inline (Jani Nikula)
>>      remove drm_print.h
>>
>> v7: Use va_format and %pV to concatenate fmt and vargs (Jani Nikula)
>>
>> Signed-off-by: Sunil Khatri <sunil.khatri at amd.com>
>> ---
>>   drivers/gpu/drm/drm_file.c | 34 ++++++++++++++++++++++++++++++++++
>>   include/drm/drm_file.h     |  3 +++
>>   2 files changed, 37 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
>> index c299cd94d3f7..7e64d84d4e2d 100644
>> --- a/drivers/gpu/drm/drm_file.c
>> +++ b/drivers/gpu/drm/drm_file.c
>> @@ -986,6 +986,40 @@ void drm_show_fdinfo(struct seq_file *m, struct 
>> file *f)
>>   }
>>   EXPORT_SYMBOL(drm_show_fdinfo);
>>   +/**
>> + * drm_file_err - Fill info string with process name and pid
>
> Update to something like:
>
> drm_file_err - Log error message associated with a drm_file client
>
>> + * @file_priv: context of interest for process name and pid
>> + * @fmt: prinf() like format string
>
> printf
>
>> + *
>> + * This update the user provided buffer with process
>> + * name and pid information for @file_priv
>
> Also stale but it may be okay to drop altogether since short 
> description feels enough for a logging helper.
>
>> + */
>> +void drm_file_err(struct drm_file *file_priv, const char *fmt, ...)
>> +{
>> +    struct task_struct *task;
>> +    struct pid *pid;
>> +    struct drm_device *dev = file_priv->minor->dev;
>> +    va_list args;
>> +    struct va_format vaf;
>
> You could tidy the declaration block a bit, usually ordering from 
> longer to narrower lines for readability but up to you.
Sure
>> +
>> +    va_start(args, fmt);
>> +    vaf.fmt = fmt;
>> +    vaf.va = &args;
>> +
>> +    mutex_lock(&file_priv->client_name_lock);
>> +    rcu_read_lock();
>> +    pid = rcu_dereference(file_priv->pid);
>> +    task = pid_task(pid, PIDTYPE_TGID);
>> +
>> +    drm_err(dev, "comm: %s pid: %d client: %s %pV", task ? 
>> task->comm : "",
>> +        task ? task->pid : 0, file_priv->client_name ?: "Unset", &vaf);
>> +
>
> Hm is task->pid the tid or tgid? Could be the same thing due getting 
> PIDTYPE_GID.. PID namespaces are always endlessly confusing to me 
> since I don't work in that area often enough.
>
There are two parameters in task_struct one is pid and tgid and both are 
different if i am not wrong. In case of multi thread pid and tgid is 
different if its one thread i guess in that case pid and tgid are same 
but even i am not 100% sure.
> And I have some bikeshedding ideas for the format, like maybe 
> consolidating with naming used in drm_clients_info() and adding some 
> separator between the client data and the log message that follows. Like:
>
> "Client %s[%d] (%s): %pV",
> task ? task->comm : "<unknown>",
> pid_nr(pid),
> file_priv->client_name ?: "<unset>",
> ...
Sure
>
> And even if I am a bit unsure about the "<unknown>", I think it 
> doesn't harm to be consistent. It is fine as is though, so you decide 
> if you want to change anything or not.
>
> If you could please double check task->pid is indeed definitely TGID:
>
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at igalia.com>
>
> Regards,
>
> Tvrtko
>
>> +    va_end(args);
>> +    rcu_read_unlock();
>> +    mutex_unlock(&file_priv->client_name_lock);
>> +}
>> +EXPORT_SYMBOL(drm_file_err);
>> +
>>   /**
>>    * mock_drm_getfile - Create a new struct file for the drm device
>>    * @minor: drm minor to wrap (e.g. #drm_device.primary)
>> diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h
>> index 94d365b22505..5c3b2aa3e69d 100644
>> --- a/include/drm/drm_file.h
>> +++ b/include/drm/drm_file.h
>> @@ -446,6 +446,9 @@ static inline bool drm_is_accel_client(const 
>> struct drm_file *file_priv)
>>       return file_priv->minor->type == DRM_MINOR_ACCEL;
>>   }
>>   +__printf(2, 3)
>> +void drm_file_err(struct drm_file *file_priv, const char *fmt, ...);
>> +
>>   void drm_file_update_pid(struct drm_file *);
>>     struct drm_minor *drm_minor_acquire(struct xarray *minors_xa, 
>> unsigned int minor_id);
>