blk-mq: create debugfs directory tree

In preparation for putting blk-mq debugging information in debugfs,
create a directory tree mirroring the one in sysfs:

    # tree -d /sys/kernel/debug/block
    /sys/kernel/debug/block
    |-- nvme0n1
    |   `-- mq
    |       |-- 0
    |       |   `-- cpu0
    |       |-- 1
    |       |   `-- cpu1
    |       |-- 2
    |       |   `-- cpu2
    |       `-- 3
    |           `-- cpu3
    `-- vda
        `-- mq
            `-- 0
                |-- cpu0
                |-- cpu1
                |-- cpu2
                `-- cpu3

Also add the scaffolding for the actual files that will go in here,
either under the hardware queue or software queue directories.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 152 insertions, 0 deletions

diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
new file mode 100644
index 0000000..01711bb
--- /dev/null
+++ b/block/blk-mq-debugfs.c
@@ -0,0 +1,152 @@
+/*
+ * Copyright (C) 2017 Facebook
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <linux/kernel.h>
+#include <linux/blkdev.h>
+#include <linux/debugfs.h>
+
+#include <linux/blk-mq.h>
+#include "blk-mq.h"
+
+struct blk_mq_debugfs_attr {
+	const char *name;
+	umode_t mode;
+	const struct file_operations *fops;
+};
+
+static struct dentry *block_debugfs_root;
+
+static const struct blk_mq_debugfs_attr blk_mq_debugfs_hctx_attrs[] = {
+};
+
+static const struct blk_mq_debugfs_attr blk_mq_debugfs_ctx_attrs[] = {
+};
+
+int blk_mq_debugfs_register(struct request_queue *q, const char *name)
+{
+	if (!block_debugfs_root)
+		return -ENOENT;
+
+	q->debugfs_dir = debugfs_create_dir(name, block_debugfs_root);
+	if (!q->debugfs_dir)
+		goto err;
+
+	if (blk_mq_debugfs_register_hctxs(q))
+		goto err;
+
+	return 0;
+
+err:
+	blk_mq_debugfs_unregister(q);
+	return -ENOMEM;
+}
+
+void blk_mq_debugfs_unregister(struct request_queue *q)
+{
+	debugfs_remove_recursive(q->debugfs_dir);
+	q->mq_debugfs_dir = NULL;
+	q->debugfs_dir = NULL;
+}
+
+static int blk_mq_debugfs_register_ctx(struct request_queue *q,
+				       struct blk_mq_ctx *ctx,
+				       struct dentry *hctx_dir)
+{
+	struct dentry *ctx_dir;
+	char name[20];
+	int i;
+
+	snprintf(name, sizeof(name), "cpu%u", ctx->cpu);
+	ctx_dir = debugfs_create_dir(name, hctx_dir);
+	if (!ctx_dir)
+		return -ENOMEM;
+
+	for (i = 0; i < ARRAY_SIZE(blk_mq_debugfs_ctx_attrs); i++) {
+		const struct blk_mq_debugfs_attr *attr;
+
+		attr = &blk_mq_debugfs_ctx_attrs[i];
+		if (!debugfs_create_file(attr->name, attr->mode, ctx_dir, ctx,
+					 attr->fops))
+			return -ENOMEM;
+	}
+
+	return 0;
+}
+
+static int blk_mq_debugfs_register_hctx(struct request_queue *q,
+					struct blk_mq_hw_ctx *hctx)
+{
+	struct blk_mq_ctx *ctx;
+	struct dentry *hctx_dir;
+	char name[20];
+	int i;
+
+	snprintf(name, sizeof(name), "%u", hctx->queue_num);
+	hctx_dir = debugfs_create_dir(name, q->mq_debugfs_dir);
+	if (!hctx_dir)
+		return -ENOMEM;
+
+	for (i = 0; i < ARRAY_SIZE(blk_mq_debugfs_hctx_attrs); i++) {
+		const struct blk_mq_debugfs_attr *attr;
+
+		attr = &blk_mq_debugfs_hctx_attrs[i];
+		if (!debugfs_create_file(attr->name, attr->mode, hctx_dir, hctx,
+					 attr->fops))
+			return -ENOMEM;
+	}
+
+	hctx_for_each_ctx(hctx, ctx, i) {
+		if (blk_mq_debugfs_register_ctx(q, ctx, hctx_dir))
+			return -ENOMEM;
+	}
+
+	return 0;
+}
+
+int blk_mq_debugfs_register_hctxs(struct request_queue *q)
+{
+	struct blk_mq_hw_ctx *hctx;
+	int i;
+
+	if (!q->debugfs_dir)
+		return -ENOENT;
+
+	q->mq_debugfs_dir = debugfs_create_dir("mq", q->debugfs_dir);
+	if (!q->mq_debugfs_dir)
+		goto err;
+
+	queue_for_each_hw_ctx(q, hctx, i) {
+		if (blk_mq_debugfs_register_hctx(q, hctx))
+			goto err;
+	}
+
+	return 0;
+
+err:
+	blk_mq_debugfs_unregister_hctxs(q);
+	return -ENOMEM;
+}
+
+void blk_mq_debugfs_unregister_hctxs(struct request_queue *q)
+{
+	debugfs_remove_recursive(q->mq_debugfs_dir);
+	q->mq_debugfs_dir = NULL;
+}
+
+void blk_mq_debugfs_init(void)
+{
+	block_debugfs_root = debugfs_create_dir("block", NULL);
+}