[PATCH 1/2] of: Make device nodes kobjects so they show up in sysfs

Grant Likely
2013-03-20T14:51:35Z

Device tree nodes are already treated as objects, and we already want to
expose them to userspace which is done using the /proc filesystem today.
Right now the kernel has to do a lot of work to keep the /proc view in
sync with the in-kernel representation. If device_nodes are switched to
be kobjects then the device tree code can be a whole lot simpler. It
also turns out that switching to using /sysfs from /proc results in
smaller code and data size, and the userspace ABI won't change if
/proc/device-tree symlinks to /sys/device-tree

Switching to sysfs does introduce two limitations however. First, normal
sysfs attributes have a maximum size of PAGE_SIZE. Any properties larger
than 4k will still show up in sysfs, but attempting to read them will
result in truncated data. Practically speaking this should not be an
issue assuming large binary blobs aren't encoded into the device tree.

Second, all normal sysfs attributes report their size as 4096 bytes
instead of the actual property size reported in /proc/device-tree. It is
possible that this change will cause some userspace tools to break.

Both of the above problems can be worked around by using
sysfs_create_bin_file() instead of sysfs_create_file(), but doing so
adds an additional 20 to 40 bytes of overhead per property. A device
tree has a lot of properties in it. That overhead will very quickly add
up. The other option is to create a new custom sysfs attribute type
would solve the problem without additional overhead, but at the cost of
more complexity in the sysfs support code. However, I'm hopeful that
these problems are just imaginary and we can stick with normal sysfs
attributes.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: David S. Miller <davem@davemloft.net>
---
Documentation/ABI/testing/sysfs-firmware-ofw | 28 ++++++
drivers/of/Kconfig | 2 +-
drivers/of/base.c | 121 ++++++++++++++++++++++++--
drivers/of/fdt.c | 3 +-
drivers/of/pdt.c | 4 +-
include/linux/of.h | 9 +-
6 files changed, 154 insertions(+), 13 deletions(-)
create mode 100644 Documentation/ABI/testing/sysfs-firmware-ofw

diff --git a/Documentation/ABI/testing/sysfs-firmware-ofw b/Documentation/ABI/testing/sysfs-firmware-ofw
new file mode 100644
index 0000000..5ef9a77
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-firmware-ofw
@@ -0,0 +1,28 @@
+What: /sys/firmware/ofw/../device-tree/
+Date: March 2013
+Contact: Grant Likely <grant.likely@secretlab.ca>
+Description:
+ When using OpenFirmware or a Flattened Device Tree to enumerate
+ hardware, the device tree structure will be exposed in this
+ directory.
+
+ It is possible for multiple device-tree directories to exist.
+ Some device drivers use a separate detached device tree which
+ have no attachment to the system tree and will appear in a
+ different subdirectory under /sys/firmware/ofw.
+
+ Userspace must not use the /sys/firmware/ofw/../device-tree
+ path directly, but instead should follow /proc/device-tree
+ symlink. It is possible that the absolute path will change
+ in the future, but the symlink is the stable ABI.
+
+ The /proc/device-tree symlink replaces the devicetree /proc
+ filesystem support, and has largely the same semantics and
+ should be compatible with existing userspace.
+
+ The contents of /sys/firmware/ofw/../device-tree is a
+ hierarchy of directories, one per device tree node. The
+ directory name is the resolved path component name (node
+ name plus address). Properties are represented as files
+ in the directory. The contents of each file is the exact
+ binary data from the device tree.
diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
index d37bfcf..d2d7be9 100644
--- a/drivers/of/Kconfig
+++ b/drivers/of/Kconfig
@@ -38,7 +38,7 @@ config OF_PROMTREE
# Hardly any platforms need this. It is safe to select, but only do so if you
# need it.
config OF_DYNAMIC
- bool
+ def_bool y

config OF_ADDRESS
def_bool y
diff --git a/drivers/of/base.c b/drivers/of/base.c
index 321d3ef..363e98b 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -22,6 +22,7 @@
#include <linux/of.h>
#include <linux/spinlock.h>
#include <linux/slab.h>
+#include <linux/string.h>
#include <linux/proc_fs.h>

#include "of_private.h"
@@ -33,6 +34,12 @@ EXPORT_SYMBOL(of_allnodes);
struct device_node *of_chosen;
struct device_node *of_aliases;

+static struct kset *of_kset;
+
+/*
+ * Used to protect the of_aliases; but also overloaded to hold off addition of
+ * nodes to sysfs
+ */
DEFINE_MUTEX(of_aliases_mutex);

/* use when traversing tree through the allnext, child, sibling,
@@ -83,14 +90,14 @@ EXPORT_SYMBOL(of_n_size_cells);
struct device_node *of_node_get(struct device_node *node)
{
if (node)
- kref_get(&node->kref);
+ kobject_get(&node->kobj);
return node;
}
EXPORT_SYMBOL(of_node_get);

-static inline struct device_node *kref_to_device_node(struct kref *kref)
+static inline struct device_node *kobj_to_device_node(struct kobject *kobj)
{
- return container_of(kref, struct device_node, kref);
+ return container_of(kobj, struct device_node, kobj);
}

/**
@@ -100,16 +107,15 @@ static inline struct device_node *kref_to_device_node(struct kref *kref)
* In of_node_put() this function is passed to kref_put()
* as the destructor.
*/
-static void of_node_release(struct kref *kref)
+static void of_node_release(struct kobject *kobj)
{
- struct device_node *node = kref_to_device_node(kref);
+ struct device_node *node = kobj_to_device_node(kobj);
struct property *prop = node->properties;

/* We should never be releasing nodes that haven't been detached. */
if (!of_node_check_flag(node, OF_DETACHED)) {
pr_err("ERROR: Bad of_node_put() on %s\n", node->full_name);
dump_stack();
- kref_init(&node->kref);
return;
}

@@ -142,11 +148,110 @@ static void of_node_release(struct kref *kref)
void of_node_put(struct device_node *node)
{
if (node)
- kref_put(&node->kref, of_node_release);
+ kobject_put(&node->kobj);
}
EXPORT_SYMBOL(of_node_put);
#endif /* CONFIG_OF_DYNAMIC */

+ssize_t of_node_sysfs_show(struct kobject *kobj, struct attribute *attr, char *buf)
+{
+ struct property *prop = container_of(attr, struct property, attr);
+ int length = prop->length;
+
+ if (length >= PAGE_SIZE)
+ length = PAGE_SIZE-1;
+ memcpy(buf, prop->value, length);
+ return length;
+}
+
+struct sysfs_ops of_node_sysfs_ops = {
+ .show = of_node_sysfs_show,
+};
+
+struct kobj_type of_node_ktype = {
+ .release = of_node_release,
+ .sysfs_ops = &of_node_sysfs_ops,
+};
+
+static bool of_init_complete = false;
+static int __of_node_add(struct device_node *np)
+{
+ const char *name;
+ struct property *pp;
+ static int extra = 0;
+ int rc;
+
+ np->kobj.kset = of_kset;
+ if (!np->parent) {
+ /* Nodes without parents are new top level trees */
+ rc = kobject_add(&np->kobj, NULL, "device-tree-%i", extra++);
+ } else {
+ name = kbasename(np->full_name);
+ if (!name || !name[0])
+ return -EINVAL;
+ rc = kobject_add(&np->kobj, &np->parent->kobj, "%s", name);
+ }
+ if (rc)
+ return rc;
+
+ for_each_property_of_node(np, pp) {
+ /*
+ * Don't leak password data. Note: if this is ever switched to use
+ * sysfs_create_bin_file(), then it is very important to not expose
+ * the size of the password in the inode. If 'secure' is set, then
+ * the inode length must be reported as '0'
+ */
+ bool secure = strncmp(pp->name, "security-", 9) == 0;
+ pp->attr.name = pp->name;
+ pp->attr.mode = secure ? S_IRUSR : S_IRUGO;
+ rc = sysfs_create_file(&np->kobj, &pp->attr);
+ WARN(rc, "error creating device node attribute\n");
+ }
+
+ return 0;
+}
+
+int of_node_add(struct device_node *np)
+{
+ int rc = 0;
+ kobject_init(&np->kobj, &of_node_ktype);
+ mutex_lock(&of_aliases_mutex);
+ if (of_init_complete)
+ rc = __of_node_add(np);
+ mutex_unlock(&of_aliases_mutex);
+ return rc;
+}
+
+#if defined(CONFIG_OF_DYNAMIC)
+static void of_node_remove(struct device_node *np)
+{
+ struct property *pp;
+
+ for_each_property_of_node(np, pp)
+ sysfs_remove_file(&np->kobj, &pp->attr);
+
+ kobject_del(&np->kobj);
+}
+#endif
+
+static int __init of_init(void)
+{
+ struct device_node *np;
+
+ of_kset = kset_create_and_add("ofw", NULL, firmware_kobj);
+ if (!of_kset)
+ return -ENOMEM;
+
+ /* Make sure all nodes added before this time get added to sysfs */
+ mutex_lock(&of_aliases_mutex);
+ for_each_of_allnodes(np)
+ __of_node_add(np);
+ of_init_complete = true;
+ mutex_unlock(&of_aliases_mutex);
+ return 0;
+}
+core_initcall(of_init);
+
static struct property *__of_find_property(const struct device_node *np,
const char *name, int *lenp)
{
@@ -1445,6 +1550,7 @@ int of_attach_node(struct device_node *np)
of_allnodes = np;
raw_spin_unlock_irqrestore(&devtree_lock, flags);

+ of_node_add(np);
of_add_proc_dt_entry(np);
return 0;
}
@@ -1526,6 +1632,7 @@ int of_detach_node(struct device_node *np)
raw_spin_unlock_irqrestore(&devtree_lock, flags);

of_remove_proc_dt_entry(np);
+ of_node_remove(np);
return rc;
}
#endif /* defined(CONFIG_OF_DYNAMIC) */
diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index 808be06..8807059 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c
@@ -232,7 +232,6 @@ static unsigned long unflatten_dt_node(struct boot_param_header *blob,
dad->next->sibling = np;
dad->next = np;
}
- kref_init(&np->kref);
}
/* process properties */
while (1) {
@@ -327,6 +326,8 @@ static unsigned long unflatten_dt_node(struct boot_param_header *blob,
np->name = "<NULL>";
if (!np->type)
np->type = "<NULL>";
+
+ of_node_add(np);
}
while (tag == OF_DT_BEGIN_NODE || tag == OF_DT_NOP) {
if (tag == OF_DT_NOP)
diff --git a/drivers/of/pdt.c b/drivers/of/pdt.c
index 37b56fd..2d9d7e1 100644
--- a/drivers/of/pdt.c
+++ b/drivers/of/pdt.c
@@ -180,8 +180,6 @@ static struct device_node * __init of_pdt_create_node(phandle node,
of_pdt_incr_unique_id(dp);
dp->parent = parent;

- kref_init(&dp->kref);
-
dp->name = of_pdt_get_one_property(node, "name");
dp->type = of_pdt_get_one_property(node, "device_type");
dp->phandle = node;
@@ -216,6 +214,7 @@ static struct device_node * __init of_pdt_build_tree(struct device_node *parent,
*nextp = &dp->allnext;

dp->full_name = of_pdt_build_full_name(dp);
+ of_node_add(dp);

dp->child = of_pdt_build_tree(dp,
of_pdt_prom_ops->getchild(node), nextp);
@@ -246,6 +245,7 @@ void __init of_pdt_build_devicetree(phandle root_node, struct of_pdt_ops *ops)
of_allnodes->path_component_name = "";
#endif
of_allnodes->full_name = "/";
+ of_node_add(of_allnodes);

nextp = &of_allnodes->allnext;
of_allnodes->child = of_pdt_build_tree(of_allnodes,
diff --git a/include/linux/of.h b/include/linux/of.h
index a0f1292..2399c8f 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -18,7 +18,7 @@
#include <linux/types.h>
#include <linux/bitops.h>
#include <linux/errno.h>
-#include <linux/kref.h>
+#include <linux/kobject.h>
#include <linux/mod_devicetable.h>
#include <linux/spinlock.h>
#include <linux/topology.h>
@@ -37,6 +37,7 @@ struct property {
struct property *next;
unsigned long _flags;
unsigned int unique_id;
+ struct attribute attr;
};

#if defined(CONFIG_SPARC)
@@ -57,7 +58,7 @@ struct device_node {
struct device_node *next; /* next device of same type */
struct device_node *allnext; /* next in list of all nodes */
struct proc_dir_entry *pde; /* this node's proc directory */
- struct kref kref;
+ struct kobject kobj;
unsigned long _flags;
void *data;
#if defined(CONFIG_SPARC)
@@ -74,6 +75,8 @@ struct of_phandle_args {
uint32_t args[MAX_PHANDLE_ARGS];
};

+extern int of_node_add(struct device_node *node);
+
#ifdef CONFIG_OF_DYNAMIC
extern struct device_node *of_node_get(struct device_node *node);
extern void of_node_put(struct device_node *node);
@@ -165,6 +168,8 @@ static inline const char *of_node_full_name(const struct device_node *np)
return np ? np->full_name : "<no-node>";
}

+#define for_each_of_allnodes(dn) \
+ for (dn = of_allnodes; dn; dn = dn->allnext)
extern struct device_node *of_find_node_by_name(struct device_node *from,
const char *name);
#define for_each_node_by_name(dn, name) \
--
1.7.10.4