Re: [PATCH v3 1/4] drm: add function drm_file_err to print proc information too

["Khatri, Sunil" <sukhatri@amd.com>]

On 4/16/2025 12:37 PM, Tvrtko Ursulin wrote:
>
> On 15/04/2025 19:43, Sunil Khatri wrote:
>> Add a drm helper function which get the process information for
>> the drm_file and append the process information using the existing
>> drm_err.
>>
>> Signed-off-by: Sunil Khatri <sunil.khatri@amd.com>
>> ---
>>   include/drm/drm_file.h | 40 ++++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 40 insertions(+)
>>
>> diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h
>> index 94d365b22505..e329299a2b2c 100644
>> --- a/include/drm/drm_file.h
>> +++ b/include/drm/drm_file.h
>> @@ -37,6 +37,7 @@
>>   #include <uapi/drm/drm.h>
>>     #include <drm/drm_prime.h>
>> +#include <drm/drm_print.h>
>>     struct dma_fence;
>>   struct drm_file;
>> @@ -446,6 +447,45 @@ static inline bool drm_is_accel_client(const 
>> struct drm_file *file_priv)
>>       return file_priv->minor->type == DRM_MINOR_ACCEL;
>>   }
>>   +/**
>> + * drm_file_err - Fill info string with process name and pid
>> + * @file_priv: context of interest for process name and pid
>> + * @fmt: prinf() like format string
>> + *
>> + * This update the user provided buffer with process
>> + * name and pid information for @file_priv
>> + */
>> +__printf(2, 3)
>> +static inline 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;
>> +    char new_fmt[256];
>> +    char final_fmt[512];
>> +    va_list args;
>> +
>> +    mutex_lock(&file_priv->client_name_lock);
>> +    rcu_read_lock();
>> +    pid = rcu_dereference(file_priv->pid);
>> +    task = pid_task(pid, PIDTYPE_TGID);
>> +
>> +    if (drm_WARN_ON_ONCE(dev, !task))
>> +        return;
>> +
>> +    snprintf(new_fmt, sizeof(new_fmt), "proc:%s pid:%d 
>> client_name:%s %s",
>> +        task->comm, task->pid, file_priv->client_name ?: "Unset", fmt);
>> +
>> +    va_start(args, fmt);
>> +    vsnprintf(final_fmt, sizeof(final_fmt), new_fmt, args);
>> +
>> +    drm_err(dev, "%s", final_fmt);
>> +    va_end(args);
>> +
>> +    rcu_read_unlock();
>> +    mutex_unlock(&file_priv->client_name_lock);
>> +}
>> +
>
> I was hoping something primitive could be enough. With no temporary 
> stack space required. Primitive on the level of (but simplified for 
> illustration purpose):
>
> #define some_err(_file, _fmt, ...) \
>     drm_err(dev, "client-%s: " _fmt, (_this)->client_name, ##__VA_ARGS__)
I also thought of doing it similarly but that dint work. There was lot 
of code to get the process name and pid along with client_name too. So 
##__VA_ARGS__ dont work as soon as its a function and not macro.
Also drm_err gave me errors and this is the way i find it not 
complaining. new_fmt is a string directly anymore and hence need to %s 
to pass but then the drm_err complain too many args for args to pass. So 
i have to combine new_fmt and args in one to get final_fmt and atleast 
functionally it worked.

Yesterday even i though that i would be as simple as adding a macro.
>
> Am I missing something or that would work?
>
> Regards,
>
> Tvrtko
>
>>   void drm_file_update_pid(struct drm_file *);
>>     struct drm_minor *drm_minor_acquire(struct xarray *minors_xa, 
>> unsigned int minor_id);
>