linux-kernel - Re: [PATCH 3/3] proc: use idr tgid tag hint to iterate pids in readdir

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Date:   Wed, 15 Jun 2022 14:44:27 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Brian Foster <bfoster@...hat.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        ikent@...hat.com, onestero@...hat.com
Subject: Re: [PATCH 3/3] proc: use idr tgid tag hint to iterate pids in
 readdir

On Tue, Jun 14, 2022 at 02:09:49PM -0400, Brian Foster wrote:
> +++ b/include/linux/idr.h
> @@ -185,6 +185,20 @@ static inline bool idr_is_group_lead(struct idr *idr, unsigned long id)
>  	return radix_tree_tag_get(&idr->idr_rt, id, IDR_TGID);
>  }
>  
> +/*
> + * Find the next id with a potentially associated TGID task using the internal
> + * tag. Task association is not guaranteed and must be checked explicitly.
> + */
> +static inline struct pid *find_tgid_pid(struct idr *idr, unsigned long id)
> +{
> +	struct pid *pid;
> +
> +	if (radix_tree_gang_lookup_tag(&idr->idr_rt, (void **) &pid, id, 1,
> +				       IDR_TGID) != 1)
> +		return NULL;
> +	return pid;
> +}

The IDR is a generic data structure, and shouldn't know anything about
PIDs, TGIDs or tasks.