[RFC PATCH 2/8] block: Add block device LED trigger list

[Ian Pilcher <arequipeno@gmail.com>]

* New config option (CONFIG_BLK_LED_TRIGGERS) to enable/disable
  block device LED triggers

* New file - block/blk-ledtrig.c

* Use a linked list of dynamically allocated triggers.  There
  aren't likely to be that many of them, and the list is only
  searched when creating/deleting a trigger or setting/clearing
  a device/trigger association - none of which should occur very
  often.

Signed-off-by: Ian Pilcher <arequipeno@gmail.com>
---
 block/Kconfig       | 10 +++++++++
 block/Makefile      |  1 +
 block/blk-ledtrig.c | 51 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 62 insertions(+)
 create mode 100644 block/blk-ledtrig.c

diff --git a/block/Kconfig b/block/Kconfig
index fd732aede922..051488413d6e 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -220,6 +220,16 @@ config BLK_INLINE_ENCRYPTION_FALLBACK
 	  by falling back to the kernel crypto API when inline
 	  encryption hardware is not present.
 
+config BLK_LED_TRIGGERS
+	bool "Enable block device LED triggers"
+	depends on LEDS_TRIGGERS
+	help
+	  Enabling this allows LED triggers to be created and
+	  associated with block devices via sysfs/udev (or an
+	  in-kernel API).  These trigers can be used to drive
+	  physical or user-space activity indicators.  See
+	  Documentation/block/led-triggers.rst.
+
 menu "Partition Types"
 
 source "block/partitions/Kconfig"
diff --git a/block/Makefile b/block/Makefile
index bfbe4e13ca1e..bcd97ee26462 100644
--- a/block/Makefile
+++ b/block/Makefile
@@ -42,3 +42,4 @@ obj-$(CONFIG_BLK_SED_OPAL)	+= sed-opal.o
 obj-$(CONFIG_BLK_PM)		+= blk-pm.o
 obj-$(CONFIG_BLK_INLINE_ENCRYPTION)	+= keyslot-manager.o blk-crypto.o
 obj-$(CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK)	+= blk-crypto-fallback.o
+obj-$(CONFIG_BLK_LED_TRIGGERS)	+= blk-ledtrig.o
diff --git a/block/blk-ledtrig.c b/block/blk-ledtrig.c
new file mode 100644
index 000000000000..345a3b6bdbc6
--- /dev/null
+++ b/block/blk-ledtrig.c
@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+/*
+ *	Block device LED triggers
+ *
+ *	Copyright 2021 Ian Pilcher <arequipeno@gmail.com>
+ */
+
+#include <linux/leds.h>
+#include <linux/list.h>
+#include <linux/mutex.h>
+
+
+/*
+ *
+ *	The list of block device LED triggers
+ *
+ */
+
+struct blk_ledtrig {
+	struct led_trigger	trigger;
+	struct list_head	list_node;
+	struct mutex		refcount_mutex;
+	int			refcount;
+	char			name[];
+};
+
+LIST_HEAD(blk_ledtrig_list);
+DEFINE_MUTEX(blk_ledtrig_list_mutex);
+
+static inline
+struct blk_ledtrig *blk_ledtrig_from_node(struct list_head *const node)
+{
+	return container_of(node, struct blk_ledtrig, list_node);
+}
+
+// Caller must hold blk_ledtrig_list_mutex
+static struct blk_ledtrig *blk_ledtrig_find(const char *const name,
+					    const size_t len)
+{
+	struct blk_ledtrig *t;
+	struct list_head *n;
+
+	list_for_each(n, &blk_ledtrig_list) {
+		t = blk_ledtrig_from_node(n);
+		if (strlen(t->name) == len && memcmp(name, t->name, len) == 0)
+			return t;
+	}
+
+	return NULL;
+}
-- 
2.31.1