[ndctl PATCH v4 06/10] libdaxctl: add an interface to get the mode for a dax device

[Vishal Verma <vishal.l.verma@intel.com>]

In preparation for a reconfigure-device command, add an interface to
retrieve the 'mode' of a dax device. This will allow the
reconfigure-device command (and via daxctl_dev_to_json()), also
daxctl-list) to print the mode on device listings via a list command or
immediately after a mode change.

Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
---
 daxctl/lib/libdaxctl.c   | 41 ++++++++++++++++++++++++++++++++++++++++
 daxctl/lib/libdaxctl.sym |  1 +
 daxctl/libdaxctl.h       |  1 +
 util/json.c              | 14 ++++++++++++++
 4 files changed, 57 insertions(+)

diff --git a/daxctl/lib/libdaxctl.c b/daxctl/lib/libdaxctl.c
index 46dbd63..9d23d12 100644
--- a/daxctl/lib/libdaxctl.c
+++ b/daxctl/lib/libdaxctl.c
@@ -12,6 +12,8 @@
  */
 #include <stdio.h>
 #include <errno.h>
+#include <limits.h>
+#include <libgen.h>
 #include <stdlib.h>
 #include <dirent.h>
 #include <unistd.h>
@@ -836,6 +838,45 @@ DAXCTL_EXPORT int daxctl_dev_disable(struct daxctl_dev *dev)
 	return 0;
 }
 
+DAXCTL_EXPORT enum daxctl_dev_mode daxctl_dev_get_mode(struct daxctl_dev *dev)
+{
+	const char *devname = daxctl_dev_get_devname(dev);
+	struct daxctl_ctx *ctx = daxctl_dev_get_ctx(dev);
+	int rc = DAXCTL_DEV_MODE_UNKNOWN;
+	char path[200];
+	const int len = sizeof(path);
+	char *mod_path, *mod_base;
+
+	if (!daxctl_dev_is_enabled(dev))
+		return rc;
+
+	/* dax-class model only has conventional devdax devices */
+	if (ctx->subsys != DAX_BUS)
+		return DAXCTL_DEV_MODE_DEVDAX;
+
+	if (snprintf(path, len, "%s/driver/module", dev->dev_path) >= len) {
+		err(ctx, "%s: buffer too small!\n", devname);
+		return -ENXIO;
+	}
+
+	mod_path = realpath(path, NULL);
+	if (!mod_path) {
+		rc = -errno;
+		err(ctx, "%s:  unable to determine module: %s\n", devname,
+			strerror(errno));
+		return rc;
+	}
+
+	mod_base = basename(mod_path);
+	if (strcmp(mod_base, dax_modules[DAXCTL_DEV_MODE_RAM]) == 0)
+		rc = DAXCTL_DEV_MODE_RAM;
+	else if (strcmp(mod_base, dax_modules[DAXCTL_DEV_MODE_DEVDAX]) == 0)
+		rc = DAXCTL_DEV_MODE_DEVDAX;
+
+	free(mod_path);
+	return rc;
+}
+
 DAXCTL_EXPORT struct daxctl_ctx *daxctl_dev_get_ctx(struct daxctl_dev *dev)
 {
 	return dev->region->ctx;
diff --git a/daxctl/lib/libdaxctl.sym b/daxctl/lib/libdaxctl.sym
index cc47ed6..d53976d 100644
--- a/daxctl/lib/libdaxctl.sym
+++ b/daxctl/lib/libdaxctl.sym
@@ -62,4 +62,5 @@ global:
 	daxctl_dev_online_node;
 	daxctl_dev_offline_node;
 	daxctl_dev_node_is_online;
+	daxctl_dev_get_mode;
 } LIBDAXCTL_5;
diff --git a/daxctl/libdaxctl.h b/daxctl/libdaxctl.h
index db0d4ea..4f9088f 100644
--- a/daxctl/libdaxctl.h
+++ b/daxctl/libdaxctl.h
@@ -76,6 +76,7 @@ int daxctl_dev_enable_ram(struct daxctl_dev *dev);
 int daxctl_dev_online_node(struct daxctl_dev *dev);
 int daxctl_dev_offline_node(struct daxctl_dev *dev);
 int daxctl_dev_node_is_online(struct daxctl_dev *dev);
+enum daxctl_dev_mode daxctl_dev_get_mode(struct daxctl_dev *dev);
 
 #define daxctl_dev_foreach(region, dev) \
         for (dev = daxctl_dev_get_first(region); \
diff --git a/util/json.c b/util/json.c
index b7ce719..4f13222 100644
--- a/util/json.c
+++ b/util/json.c
@@ -271,6 +271,7 @@ struct json_object *util_daxctl_dev_to_json(struct daxctl_dev *dev,
 {
 	const char *devname = daxctl_dev_get_devname(dev);
 	struct json_object *jdev, *jobj;
+	enum daxctl_dev_mode mode;
 	int node;
 
 	jdev = json_object_new_object();
@@ -292,6 +293,19 @@ struct json_object *util_daxctl_dev_to_json(struct daxctl_dev *dev,
 			json_object_object_add(jdev, "numa_node", jobj);
 	}
 
+	mode = daxctl_dev_get_mode(dev);
+	if (mode > 0) {
+		jobj = NULL;
+		if (mode == DAXCTL_DEV_MODE_RAM)
+			jobj = json_object_new_string("system-ram");
+		else if (mode == DAXCTL_DEV_MODE_DEVDAX)
+			jobj = json_object_new_string("devdax");
+		else
+			jobj = json_object_new_string("unknown");
+		if (jobj)
+			json_object_object_add(jdev, "mode", jobj);
+	}
+
 	return jdev;
 }
 
-- 
2.20.1

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