[PATCH v2 1/4] drm: function to get process name and pid

[Christian König]

Am 15.04.25 um 13:40 schrieb Tvrtko Ursulin:
>
> On 15/04/2025 12:25, Sunil Khatri wrote:
>> Add helper function which get the process information for
>> the drm_file and updates the user provided character buffer
>> with the information of process name and pid as a string.
>>
>> Signed-off-by: Sunil Khatri <sunil.khatri at amd.com>
>> ---
>>   drivers/gpu/drm/drm_file.c | 34 ++++++++++++++++++++++++++++++++++
>>   include/drm/drm_file.h     |  1 +
>>   2 files changed, 35 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
>> index c299cd94d3f7..728a60975f5e 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_process_info - Fill info string with process name and pid
>> + * @file_priv: context of interest for process name and pid
>> + * @proc_info: user char ptr to write the string to
>> + * @buff_size: size of the buffer passed for the string
>> + *
>> + * This update the user provided buffer with process
>> + * name and pid information for @file_priv
>> + */
>> +void drm_process_info(struct drm_file *file_priv, char *proc_info, size_t buff_size)
>> +{
>> +    struct task_struct *task;
>> +    struct pid *pid;
>> +    struct drm_device *dev = file_priv->minor->dev;
>> +
>> +    if (!proc_info) {
>> +        drm_WARN_ON_ONCE(dev, "Invalid user buffer\n");
>> +        return;
>> +    }
>
> I think this should be:
>
> if (drm_WARN_ON_ONCE(dev, !proc_info))
>     return;
>
>> +
>> +    mutex_lock(&file_priv->client_name_lock);
>> +    rcu_read_lock();
>> +    pid = rcu_dereference(file_priv->pid);
>> +    task = pid_task(pid, PIDTYPE_TGID);
>> +    if (task)
>> +        snprintf(proc_info, buff_size, "client_name:%s proc:%s pid:%d",
>> +             file_priv->client_name ? file_priv->client_name : "Unset",
>> +             task->comm, task->pid);
>
> Probably bad to return uninitialised string for the !task case.
>
> Also, now that you added client name the case to move towards the helper which does not need a temporary buffer, like I was suggesting drm_file_err(drm_file *, const char *, ...), is IMO even stronger. Consider if nothing else DRM_CLIENT_NAME_MAX_LEN plus the length of other fields you will be adding (the series as is can truncate). And it would be a bit unsightly to require relatively huge stack buffers in the later patches when it can all be easily avoided.

+1 for the drm_file_err() approach.

That is quite some nifty idea and could potentially be applied to quite some other cases as well.

Regards,
Christian.

>
> Regards,
>
> Tvrtko
>
>> +
>> +    rcu_read_unlock();
>> +    mutex_unlock(&file_priv->client_name_lock);
>> +}
>> +EXPORT_SYMBOL(drm_process_info);
>> +
>>   /**
>>    * 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..a972be73a615 100644
>> --- a/include/drm/drm_file.h
>> +++ b/include/drm/drm_file.h
>> @@ -507,6 +507,7 @@ void drm_print_memory_stats(struct drm_printer *p,
>>     void drm_show_memory_stats(struct drm_printer *p, struct drm_file *file);
>>   void drm_show_fdinfo(struct seq_file *m, struct file *f);
>> +void drm_process_info(struct drm_file *file_priv, char *proc_info, size_t buff_size);
>>     struct file *mock_drm_getfile(struct drm_minor *minor, unsigned int flags);
>>   
>