Subject: Re: [PATCH v4 06/39] netfs: Add a procfile to list in-progress requests

From: Jeff Layton <[email-masked]>
Date: Wed, 13 Dec 2023 10:59:27 -0500

On Wed, 2023-12-13 at 15:23 +0000, David Howells wrote:
> Add a procfile, /proc/fs/netfs/requests, to list in-progress netfslib I/O
> requests.
> 

This should probably be in debugfs. I could see us wanting to improve
this interface over time. That's harder with procfs but with debugfs
we'd have carte blanche to do so.

> Signed-off-by: David Howells <[email-masked]>
> cc: Jeff Layton <[email-masked]>
> cc: [email-masked]
> cc: [email-masked]
> cc: [email-masked]
> ---
>  fs/netfs/internal.h   | 22 ++++++++++++++
>  fs/netfs/main.c       | 69 ++++++++++++++++++++++++++++++++++++++++++-
>  fs/netfs/objects.c    |  4 ++-
>  include/linux/netfs.h |  6 +++-
>  4 files changed, 98 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
> index a15fe67e1db7..937d9a22f178 100644
> --- a/fs/netfs/internal.h
> +++ b/fs/netfs/internal.h
> @@ -33,6 +33,28 @@ int netfs_begin_read(struct netfs_io_request *rreq, bool sync);
>   * main.c
>   */
>  extern unsigned int netfs_debug;
> +extern struct list_head netfs_io_requests;
> +extern spinlock_t netfs_proc_lock;
> +
> +#ifdef CONFIG_PROC_FS
> +static inline void netfs_proc_add_rreq(struct netfs_io_request *rreq)
> +{
> +	spin_lock(&netfs_proc_lock);
> +	list_add_tail_rcu(&rreq->proc_link, &netfs_io_requests);
> +	spin_unlock(&netfs_proc_lock);
> +}
> +static inline void netfs_proc_del_rreq(struct netfs_io_request *rreq)
> +{
> +	if (!list_empty(&rreq->proc_link)) {
> +		spin_lock(&netfs_proc_lock);
> +		list_del_rcu(&rreq->proc_link);
> +		spin_unlock(&netfs_proc_lock);
> +	}
> +}
> +#else
> +static inline void netfs_proc_add_rreq(struct netfs_io_request *rreq) {}
> +static inline void netfs_proc_del_rreq(struct netfs_io_request *rreq) {}
> +#endif
>  
>  /*
>   * objects.c
> diff --git a/fs/netfs/main.c b/fs/netfs/main.c
> index c9af6e0896d3..97ce1436615b 100644
> --- a/fs/netfs/main.c
> +++ b/fs/netfs/main.c
> @@ -21,13 +21,80 @@ unsigned netfs_debug;
>  module_param_named(debug, netfs_debug, uint, S_IWUSR | S_IRUGO);
>  MODULE_PARM_DESC(netfs_debug, "Netfs support debugging mask");
>  
> +#ifdef CONFIG_PROC_FS
> +LIST_HEAD(netfs_io_requests);
> +DEFINE_SPINLOCK(netfs_proc_lock);
> +
> +static const char *netfs_origins[] = {
> +	[NETFS_READAHEAD]	= "RA",
> +	[NETFS_READPAGE]	= "RP",
> +	[NETFS_READ_FOR_WRITE]	= "RW",
> +};
> +
> +/*
> + * Generate a list of I/O requests in /proc/fs/netfs/requests
> + */
> +static int netfs_requests_seq_show(struct seq_file *m, void *v)
> +{
> +	struct netfs_io_request *rreq;
> +
> +	if (v == &netfs_io_requests) {
> +		seq_puts(m,
> +			 "REQUEST  OR REF FL ERR  OPS COVERAGE\n"
> +			 "======== == === == ==== === =========\n"
> +			 );
> +		return 0;
> +	}
> +
> +	rreq = list_entry(v, struct netfs_io_request, proc_link);
> +	seq_printf(m,
> +		   "%08x %s %3d %2lx %4d %3d @%04llx %zx/%zx",
> +		   rreq->debug_id,
> +		   netfs_origins[rreq->origin],
> +		   refcount_read(&rreq->ref),
> +		   rreq->flags,
> +		   rreq->error,
> +		   atomic_read(&rreq->nr_outstanding),
> +		   rreq->start, rreq->submitted, rreq->len);
> +	seq_putc(m, '\n');
> +	return 0;
> +}
> +
> +static void *netfs_requests_seq_start(struct seq_file *m, loff_t *_pos)
> +	__acquires(rcu)
> +{
> +	rcu_read_lock();
> +	return seq_list_start_head(&netfs_io_requests, *_pos);
> +}
> +
> +static void *netfs_requests_seq_next(struct seq_file *m, void *v, loff_t *_pos)
> +{
> +	return seq_list_next(v, &netfs_io_requests, _pos);
> +}
> +
> +static void netfs_requests_seq_stop(struct seq_file *m, void *v)
> +	__releases(rcu)
> +{
> +	rcu_read_unlock();
> +}
> +
> +static const struct seq_operations netfs_requests_seq_ops = {
> +	.start  = netfs_requests_seq_start,
> +	.next   = netfs_requests_seq_next,
> +	.stop   = netfs_requests_seq_stop,
> +	.show   = netfs_requests_seq_show,
> +};
> +#endif /* CONFIG_PROC_FS */
> +
>  static int __init netfs_init(void)
>  {
>  	int ret = -ENOMEM;
>  
>  	if (!proc_mkdir("fs/netfs", NULL))
>  		goto error;
> -
> +	if (!proc_create_seq("fs/netfs/requests", S_IFREG | 0444, NULL,
> +			     &netfs_requests_seq_ops))
> +		goto error_proc;
>  #ifdef CONFIG_FSCACHE_STATS
>  	if (!proc_create_single("fs/netfs/stats", S_IFREG | 0444, NULL,
>  				netfs_stats_show))
> diff --git a/fs/netfs/objects.c b/fs/netfs/objects.c
> index e17cdf53f6a7..85f428fc52e6 100644
> --- a/fs/netfs/objects.c
> +++ b/fs/netfs/objects.c
> @@ -45,6 +45,7 @@ struct netfs_io_request *netfs_alloc_request(struct address_space *mapping,
>  		}
>  	}
>  
> +	netfs_proc_add_rreq(rreq);
>  	netfs_stat(&netfs_n_rh_rreq);
>  	return rreq;
>  }
> @@ -76,12 +77,13 @@ static void netfs_free_request(struct work_struct *work)
>  		container_of(work, struct netfs_io_request, work);
>  
>  	trace_netfs_rreq(rreq, netfs_rreq_trace_free);
> +	netfs_proc_del_rreq(rreq);
>  	netfs_clear_subrequests(rreq, false);
>  	if (rreq->netfs_ops->free_request)
>  		rreq->netfs_ops->free_request(rreq);
>  	if (rreq->cache_resources.ops)
>  		rreq->cache_resources.ops->end_operation(&rreq->cache_resources);
> -	kfree(rreq);
> +	kfree_rcu(rreq, rcu);
>  	netfs_stat_d(&netfs_n_rh_rreq);
>  }
>  
> diff --git a/include/linux/netfs.h b/include/linux/netfs.h
> index 32faf6c89702..7244ddebd974 100644
> --- a/include/linux/netfs.h
> +++ b/include/linux/netfs.h
> @@ -175,10 +175,14 @@ enum netfs_io_origin {
>   * operations to a variety of data stores and then stitch the result together.
>   */
>  struct netfs_io_request {
> -	struct work_struct	work;
> +	union {
> +		struct work_struct work;
> +		struct rcu_head rcu;
> +	};
>  	struct inode		*inode;		/* The file being accessed */
>  	struct address_space	*mapping;	/* The mapping being accessed */
>  	struct netfs_cache_resources cache_resources;
> +	struct list_head	proc_link;	/* Link in netfs_iorequests */
>  	struct list_head	subrequests;	/* Contributory I/O operations */
>  	void			*netfs_priv;	/* Private data for the netfs */
>  	unsigned int		debug_id;
> 

-- 
Jeff Layton <[email-masked]>