[RFC,11/12] netfs: Put a list of regions in /proc/fs/netfs/regions

diff --git a/fs/netfs/Makefile b/fs/netfs/Makefile
index a7c3a9173ac0..62dad3d7bea0 100644
--- a/fs/netfs/Makefile
+++ b/fs/netfs/Makefile
@@ -1,6 +1,7 @@ 
 # SPDX-License-Identifier: GPL-2.0
 
 netfs-y := \
+	main.o \
 	objects.o \
 	read_helper.o \
 	write_back.o \
diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
index 381ca64062eb..a9ec6591f90a 100644
--- a/fs/netfs/internal.h
+++ b/fs/netfs/internal.h
@@ -22,6 +22,30 @@ 
 ssize_t netfs_file_direct_write(struct netfs_dirty_region *region,
 				struct kiocb *iocb, struct iov_iter *from);
 
+/*
+ * main.c
+ */
+extern struct list_head netfs_regions;
+extern spinlock_t netfs_regions_lock;
+
+#ifdef CONFIG_PROC_FS
+static inline void netfs_proc_add_region(struct netfs_dirty_region *region)
+{
+	spin_lock(&netfs_regions_lock);
+	list_add_tail_rcu(&region->proc_link, &netfs_regions);
+	spin_unlock(&netfs_regions_lock);
+}
+static inline void netfs_proc_del_region(struct netfs_dirty_region *region)
+{
+	spin_lock(&netfs_regions_lock);
+	list_del_rcu(&region->proc_link);
+	spin_unlock(&netfs_regions_lock);
+}
+#else
+static inline void netfs_proc_add_region(struct netfs_dirty_region *region) {}
+static inline void netfs_proc_del_region(struct netfs_dirty_region *region) {}
+#endif
+
 /*
  * objects.c
  */
diff --git a/fs/netfs/main.c b/fs/netfs/main.c
new file mode 100644
index 000000000000..125b570efefd
--- /dev/null
+++ b/fs/netfs/main.c
@@ -0,0 +1,104 @@ 
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Network filesystem library.
+ *
+ * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/module.h>
+#include <linux/export.h>
+#include <linux/fs.h>
+#include <linux/slab.h>
+#include <linux/proc_fs.h>
+#include "internal.h"
+
+#ifdef CONFIG_PROC_FS
+LIST_HEAD(netfs_regions);
+DEFINE_SPINLOCK(netfs_regions_lock);
+
+static const char netfs_proc_region_states[] = "PRADFC";
+static const char *netfs_proc_region_types[] = {
+	[NETFS_REGION_ORDINARY]		= "ORD ",
+	[NETFS_REGION_DIO]		= "DIOW",
+	[NETFS_REGION_DSYNC]		= "DSYN",
+};
+
+/*
+ * Generate a list of regions in /proc/fs/netfs/regions
+ */
+static int netfs_regions_seq_show(struct seq_file *m, void *v)
+{
+	struct netfs_dirty_region *region;
+
+	if (v == &netfs_regions) {
+		seq_puts(m,
+			 "REGION   REF TYPE S FL DEV   INODE    DIRTY, BOUNDS, RESV\n"
+			 "======== === ==== = == ===== ======== ==============================\n"
+			 );
+		return 0;
+	}
+
+	region = list_entry(v, struct netfs_dirty_region, proc_link);
+	seq_printf(m,
+		   "%08x %3d %s %c %2lx %02x:%02x %8x %04llx-%04llx %04llx-%04llx %04llx-%04llx\n",
+		   region->debug_id,
+		   refcount_read(&region->ref),
+		   netfs_proc_region_types[region->type],
+		   netfs_proc_region_states[region->state],
+		   region->flags,
+		   0, 0, 0,
+		   region->dirty.start, region->dirty.end,
+		   region->bounds.start, region->bounds.end,
+		   region->reserved.start, region->reserved.end);
+	return 0;
+}
+
+static void *netfs_regions_seq_start(struct seq_file *m, loff_t *_pos)
+	__acquires(rcu)
+{
+	rcu_read_lock();
+	return seq_list_start_head(&netfs_regions, *_pos);
+}
+
+static void *netfs_regions_seq_next(struct seq_file *m, void *v, loff_t *_pos)
+{
+	return seq_list_next(v, &netfs_regions, _pos);
+}
+
+static void netfs_regions_seq_stop(struct seq_file *m, void *v)
+	__releases(rcu)
+{
+	rcu_read_unlock();
+}
+
+const struct seq_operations netfs_regions_seq_ops = {
+	.start  = netfs_regions_seq_start,
+	.next   = netfs_regions_seq_next,
+	.stop   = netfs_regions_seq_stop,
+	.show   = netfs_regions_seq_show,
+};
+#endif /* CONFIG_PROC_FS */
+
+static int __init netfs_init(void)
+{
+	if (!proc_mkdir("fs/netfs", NULL))
+		goto error;
+
+	if (!proc_create_seq("fs/netfs/regions", S_IFREG | 0444, NULL,
+			     &netfs_regions_seq_ops))
+		goto error_proc;
+
+	return 0;
+
+error_proc:
+	remove_proc_entry("fs/netfs", NULL);
+error:
+	return -ENOMEM;
+}
+fs_initcall(netfs_init);
+
+static void __exit netfs_exit(void)
+{
+	remove_proc_entry("fs/netfs", NULL);
+}
+module_exit(netfs_exit);
diff --git a/fs/netfs/objects.c b/fs/netfs/objects.c
index 8926b4230d91..1149f12ca8c9 100644
--- a/fs/netfs/objects.c
+++ b/fs/netfs/objects.c
@@ -60,8 +60,10 @@  struct netfs_dirty_region *netfs_alloc_dirty_region(void)
 	struct netfs_dirty_region *region;
 
 	region = kzalloc(sizeof(struct netfs_dirty_region), GFP_KERNEL);
-	if (region)
+	if (region) {
+		INIT_LIST_HEAD(&region->proc_link);
 		netfs_stat(&netfs_n_wh_region);
+	}
 	return region;
 }
 
@@ -81,6 +83,8 @@  void netfs_free_dirty_region(struct netfs_i_context *ctx,
 {
 	if (region) {
 		trace_netfs_ref_region(region->debug_id, 0, netfs_region_trace_free);
+		if (!list_empty(&region->proc_link))
+			netfs_proc_del_region(region);
 		if (ctx->ops->free_dirty_region)
 			ctx->ops->free_dirty_region(region);
 		netfs_put_flush_group(region->group);
diff --git a/fs/netfs/write_helper.c b/fs/netfs/write_helper.c
index fa048e3882ea..b1fe2d4c0df6 100644
--- a/fs/netfs/write_helper.c
+++ b/fs/netfs/write_helper.c
@@ -86,10 +86,13 @@  static void netfs_init_dirty_region(struct netfs_dirty_region *region,
 		group = list_last_entry(&ctx->flush_groups,
 					struct netfs_flush_group, group_link);
 		region->group = netfs_get_flush_group(group);
+		spin_lock(&ctx->lock);
 		list_add_tail(&region->flush_link, &group->region_list);
+		spin_unlock(&ctx->lock);
 	}
 	trace_netfs_ref_region(region->debug_id, 1, netfs_region_trace_new);
 	trace_netfs_dirty(ctx, region, NULL, netfs_dirty_trace_new);
+	netfs_proc_add_region(region);
 }
 
 /*
@@ -198,6 +201,7 @@  static struct netfs_dirty_region *netfs_split_dirty_region(
 	list_add(&tail->dirty_link, &region->dirty_link);
 	list_add(&tail->flush_link, &region->flush_link);
 	trace_netfs_dirty(ctx, tail, region, netfs_dirty_trace_split);
+	netfs_proc_add_region(tail);
 	return tail;
 }
 
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 6acf3fb170c3..43d195badb0d 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -228,6 +228,7 @@  enum netfs_region_type {
  */
 struct netfs_dirty_region {
 	struct netfs_flush_group *group;
+	struct list_head	proc_link;	/* Link in /proc/fs/netfs/regions */
 	struct list_head	active_link;	/* Link in i_context->pending/active_writes */
 	struct list_head	dirty_link;	/* Link in i_context->dirty_regions */
 	struct list_head	flush_link;	/* Link in group->region_list or