[PATCH v5 27/29] fs/resctrl: Add file system mechanism for architecture info file

[Tony Luck <tony.luck@intel.com>]

Creation of all files in the resctrl file system is under control of
the file system layer.

But some resources may need to add a file to the info/{resource}
directory for debug purposes.

Add a new rdt_resource::info_file field for the resource to specify
show() and/or write() operations. These will be called with the
rdtgroup_mutex held.

Architecture can note the file is only for debug using by setting
the rftype::flags RFTYPE_DEBUG bit.

Signed-off-by: Tony Luck <tony.luck@intel.com>
---
 include/linux/resctrl.h | 33 +++++++++++++++++++++++++++
 fs/resctrl/internal.h   | 31 ++-----------------------
 fs/resctrl/rdtgroup.c   | 50 ++++++++++++++++++++++++++++++++++++++---
 3 files changed, 82 insertions(+), 32 deletions(-)

diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index b7e15abcde23..e067007c633c 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -73,6 +73,37 @@ enum resctrl_conf_type {
 
 #define CDP_NUM_TYPES	(CDP_DATA + 1)
 
+/**
+ * struct rftype - describe each file in the resctrl file system
+ * @name:	File name
+ * @mode:	Access mode
+ * @kf_ops:	File operations
+ * @flags:	File specific RFTYPE_FLAGS_* flags
+ * @fflags:	File specific RFTYPE_* flags
+ * @seq_show:	Show content of the file
+ * @write:	Write to the file
+ */
+struct rftype {
+	char			*name;
+	umode_t			mode;
+	const struct kernfs_ops	*kf_ops;
+	unsigned long		flags;
+	unsigned long		fflags;
+
+	int (*seq_show)(struct kernfs_open_file *of,
+			struct seq_file *sf, void *v);
+	/*
+	 * write() is the generic write callback which maps directly to
+	 * kernfs write operation and overrides all other operations.
+	 * Maximum write size is determined by ->max_write_len.
+	 */
+	ssize_t (*write)(struct kernfs_open_file *of,
+			 char *buf, size_t nbytes, loff_t off);
+};
+
+/* Only rftype::flags option available to architecture code */
+#define RFTYPE_DEBUG			BIT(10)
+
 /*
  * struct pseudo_lock_region - pseudo-lock region information
  * @s:			Resctrl schema for the resource to which this
@@ -281,6 +312,7 @@ enum resctrl_schema_fmt {
  * @mbm_cfg_mask:	Bandwidth sources that can be tracked when bandwidth
  *			monitoring events can be configured.
  * @cdp_capable:	Is the CDP feature available on this resource
+ * @info_file:		Optional per-resource debug info file
  */
 struct rdt_resource {
 	int			rid;
@@ -297,6 +329,7 @@ struct rdt_resource {
 	enum resctrl_schema_fmt	schema_fmt;
 	unsigned int		mbm_cfg_mask;
 	bool			cdp_capable;
+	struct rftype		info_file;
 };
 
 /*
diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
index 1f4800cfcd6a..f13b63804c1a 100644
--- a/fs/resctrl/internal.h
+++ b/fs/resctrl/internal.h
@@ -232,7 +232,8 @@ struct rdtgroup {
 
 #define RFTYPE_RES_MB			BIT(9)
 
-#define RFTYPE_DEBUG			BIT(10)
+// RFTYPE_DEBUG available to architecture code in <linux/resctrl.h>
+//#define RFTYPE_DEBUG			BIT(10)
 
 #define RFTYPE_RES_PERF_PKG		BIT(11)
 
@@ -251,34 +252,6 @@ extern struct list_head rdt_all_groups;
 
 extern int max_name_width;
 
-/**
- * struct rftype - describe each file in the resctrl file system
- * @name:	File name
- * @mode:	Access mode
- * @kf_ops:	File operations
- * @flags:	File specific RFTYPE_FLAGS_* flags
- * @fflags:	File specific RFTYPE_* flags
- * @seq_show:	Show content of the file
- * @write:	Write to the file
- */
-struct rftype {
-	char			*name;
-	umode_t			mode;
-	const struct kernfs_ops	*kf_ops;
-	unsigned long		flags;
-	unsigned long		fflags;
-
-	int (*seq_show)(struct kernfs_open_file *of,
-			struct seq_file *sf, void *v);
-	/*
-	 * write() is the generic write callback which maps directly to
-	 * kernfs write operation and overrides all other operations.
-	 * Maximum write size is determined by ->max_write_len.
-	 */
-	ssize_t (*write)(struct kernfs_open_file *of,
-			 char *buf, size_t nbytes, loff_t off);
-};
-
 /**
  * struct mbm_state - status for each MBM counter in each domain
  * @prev_bw_bytes: Previous bytes value read for bandwidth calculation
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index e212e46e0780..f09674c209f8 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -329,6 +329,37 @@ static const struct kernfs_ops rdtgroup_kf_single_ops = {
 	.seq_show		= rdtgroup_seqfile_show,
 };
 
+static int rdtgroup_seqfile_show_locked(struct seq_file *m, void *arg)
+{
+	struct kernfs_open_file *of = m->private;
+	struct rftype *rft = of->kn->priv;
+
+	guard(mutex)(&rdtgroup_mutex);
+
+	if (rft->seq_show)
+		return rft->seq_show(of, m, arg);
+	return 0;
+}
+
+static ssize_t rdtgroup_file_write_locked(struct kernfs_open_file *of, char *buf,
+					  size_t nbytes, loff_t off)
+{
+	struct rftype *rft = of->kn->priv;
+
+	guard(mutex)(&rdtgroup_mutex);
+
+	if (rft->write)
+		return rft->write(of, buf, nbytes, off);
+
+	return -EINVAL;
+}
+
+static const struct kernfs_ops rdtgroup_kf_single_locked_ops = {
+	.atomic_write_len	= PAGE_SIZE,
+	.write			= rdtgroup_file_write_locked,
+	.seq_show		= rdtgroup_seqfile_show_locked,
+};
+
 static const struct kernfs_ops kf_mondata_ops = {
 	.atomic_write_len	= PAGE_SIZE,
 	.seq_show		= rdtgroup_mondata_show,
@@ -2162,7 +2193,7 @@ int rdtgroup_kn_mode_restore(struct rdtgroup *r, const char *name,
 	return ret;
 }
 
-static int rdtgroup_mkdir_info_resdir(void *priv, char *name,
+static int rdtgroup_mkdir_info_resdir(struct rdt_resource *r, void *priv, char *name,
 				      unsigned long fflags)
 {
 	struct kernfs_node *kn_subdir;
@@ -2177,6 +2208,19 @@ static int rdtgroup_mkdir_info_resdir(void *priv, char *name,
 	if (ret)
 		return ret;
 
+	if (r->info_file.name &&
+	    (!(r->info_file.flags & RFTYPE_DEBUG) || resctrl_debug)) {
+		r->info_file.mode = 0;
+		if (r->info_file.seq_show)
+			r->info_file.mode |= 0444;
+		if (r->info_file.write)
+			r->info_file.mode |= 0200;
+		r->info_file.kf_ops = &rdtgroup_kf_single_locked_ops;
+		ret = rdtgroup_add_file(kn_subdir, &r->info_file);
+		if (ret)
+			return ret;
+	}
+
 	ret = rdtgroup_add_files(kn_subdir, fflags);
 	if (!ret)
 		kernfs_activate(kn_subdir);
@@ -2221,7 +2265,7 @@ static int rdtgroup_create_info_dir(struct kernfs_node *parent_kn)
 	list_for_each_entry(s, &resctrl_schema_all, list) {
 		r = s->res;
 		fflags = fflags_from_resource(r) | RFTYPE_CTRL_INFO;
-		ret = rdtgroup_mkdir_info_resdir(s, s->name, fflags);
+		ret = rdtgroup_mkdir_info_resdir(r, s, s->name, fflags);
 		if (ret)
 			goto out_destroy;
 	}
@@ -2229,7 +2273,7 @@ static int rdtgroup_create_info_dir(struct kernfs_node *parent_kn)
 	for_each_mon_capable_rdt_resource(r) {
 		fflags = fflags_from_resource(r) | RFTYPE_MON_INFO;
 		sprintf(name, "%s_MON", r->name);
-		ret = rdtgroup_mkdir_info_resdir(r, name, fflags);
+		ret = rdtgroup_mkdir_info_resdir(r, r, name, fflags);
 		if (ret)
 			goto out_destroy;
 	}
-- 
2.49.0