Re: [PATCH 28/28] drm/xe/pf: Refactor strlcat() to seq_buf in sched_group_engines_read()

[Kees Cook <kees@kernel.org>]

On Tue, Sep 15, 2026 at 08:18:45AM +0000, Bill Wendling wrote:
> diff --git a/drivers/gpu/drm/xe/xe_gt_sriov_pf_debugfs.c b/drivers/gpu/drm/xe/xe_gt_sriov_pf_debugfs.c

This is the same file touched as
https://lore.kernel.org/all/20260915081910.4142719-28-morbo@google.com/
and doing the same thing, roughly? I think it'd be best to combine
these, especially since one depends on the other's addition of seq_buf.h

> index 5db7fc067c4d..548a50f74422 100644
> --- a/drivers/gpu/drm/xe/xe_gt_sriov_pf_debugfs.c
> +++ b/drivers/gpu/drm/xe/xe_gt_sriov_pf_debugfs.c
> @@ -377,8 +377,10 @@ static ssize_t sched_group_engines_read(struct file *file, char __user *buf,
>  	struct xe_hw_engine *hwe;
>  	enum xe_hw_engine_id id;
>  	char engines[128];
> +	struct seq_buf s;
> +	const char *s_str;
>  
> -	engines[0] = '\0';
> +	seq_buf_init(&s, engines, sizeof(engines));

As with the others, DECLARE_SEQ_BUF should be used.

>  	if (group < num_groups) {
>  		for_each_hw_engine(hwe, gt, id) {
> @@ -386,15 +388,14 @@ static ssize_t sched_group_engines_read(struct file *file, char __user *buf,
>  			u16 guc_logical_instance = xe_hwe_guc_logical_instance(hwe);
>  			u32 mask = groups[group].engines[guc_class];
>  
> -			if (mask & BIT(guc_logical_instance)) {
> -				strlcat(engines, hwe->name, sizeof(engines));
> -				strlcat(engines, " ", sizeof(engines));
> -			}
> +			if (mask & BIT(guc_logical_instance))
> +				seq_buf_printf(&s, "%s ", hwe->name);
>  		}
> -		strlcat(engines, "\n", sizeof(engines));
> +		seq_buf_puts(&s, "\n");
>  	}
>  
> -	return simple_read_from_buffer(buf, count, ppos, engines, strlen(engines));
> +	s_str = seq_buf_str(&s);
> +	return simple_read_from_buffer(buf, count, ppos, s_str, strlen(s_str));

While this is the correct length, it does illustrate why I think we need
a new seq_buf helper to get the strlen result detected from NUL
termination like seq_buf_str().

-Kees

-- 
Kees Cook