[PATCH] Add CONFIG_SYSFS

From: Patrick Mochel <mochel@digitalimplant.org>

Here is a patch to make sysfs optional.  Note that with CONFIG_SYSFS=n you
must specify the boot device's major:minor on the kernel boot command line
with

	root=03:01

For embedded systems, it will save a significant amount of memory during
runtime.  And, it saves 4k from the built kernel image for me.

fs/Kconfig

@@ -780,6 +780,30 @@ config PROC_KCORE
 	bool
 	default y if !ARM
 
+config SYSFS
+	bool "sysfs file system support" if EMBEDDED
+	default y
+	help
+	The sysfs filesystem is a virtual filesystem that the kernel uses to
+	export internal kernel objects, their attributes, and their
+	relationships to one another.
+
+	Users can use sysfs to ascertain useful information about the running
+	kernel, such as the devices the kernel has discovered on each bus and
+	which driver each is bound to. sysfs can also be used to tune devices
+	and other kernel subsystems.
+
+	Some system agents rely on the information in sysfs to operate.
+	/sbin/hotplug uses device and object attributes in sysfs to assist in
+	delegating policy decisions, like persistantly naming devices.
+
+	sysfs is currently used by the block subsystem to mount the root
+	partition.  If sysfs is disabled you must specify the boot device on
+	the kernel boot command line via its major and minor numbers.  For
+	example, "root=03:01" for /dev/hda1.
+
+	Designers of embedded systems may wish to say N here to conserve space.
+
 config DEVFS_FS
 	bool "/dev file system support (OBSOLETE)"
 	depends on EXPERIMENTAL

fs/Makefile

@@ -39,7 +39,7 @@ obj-$(CONFIG_QUOTACTL)		+= quota.o
 
 obj-$(CONFIG_PROC_FS)		+= proc/
 obj-y				+= partitions/
-obj-y				+= sysfs/
+obj-$(CONFIG_SYSFS)		+= sysfs/
 obj-y				+= devpts/
 
 obj-$(CONFIG_PROFILING)		+= dcookies.o

fs/namespace.c

@@ -24,7 +24,15 @@
 #include <asm/uaccess.h>
 
 extern int __init init_rootfs(void);
+
+#ifdef CONFIG_SYSFS
 extern int __init sysfs_init(void);
+#else
+static inline int sysfs_init(void)
+{
+	return 0;
+}
+#endif
 
 /* spinlock for vfsmount related operations, inplace of dcache_lock */
 spinlock_t vfsmount_lock __cacheline_aligned_in_smp = SPIN_LOCK_UNLOCKED;

include/linux/sysfs.h

@@ -18,6 +18,12 @@ struct attribute {
 	mode_t			mode;
 };
 
+struct attribute_group {
+	char			* name;
+	struct attribute	** attrs;
+};
+
+
 struct bin_attribute {
 	struct attribute	attr;
 	size_t			size;
@@ -25,14 +31,13 @@ struct bin_attribute {
 	ssize_t (*write)(struct kobject *, char *, loff_t, size_t);
 };
 
-int sysfs_create_bin_file(struct kobject * kobj, struct bin_attribute * attr);
-int sysfs_remove_bin_file(struct kobject * kobj, struct bin_attribute * attr);
-
 struct sysfs_ops {
 	ssize_t	(*show)(struct kobject *, struct attribute *,char *);
 	ssize_t	(*store)(struct kobject *,struct attribute *,const char *, size_t);
 };
 
+#ifdef CONFIG_SYSFS
+
 extern int
 sysfs_create_dir(struct kobject *);
 
@@ -57,13 +62,75 @@ sysfs_create_link(struct kobject * kobj, struct kobject * target, char * name);
 extern void
 sysfs_remove_link(struct kobject *, char * name);
 
-
-struct attribute_group {
-	char			* name;
-	struct attribute	** attrs;
-};
+int sysfs_create_bin_file(struct kobject * kobj, struct bin_attribute * attr);
+int sysfs_remove_bin_file(struct kobject * kobj, struct bin_attribute * attr);
 
 int sysfs_create_group(struct kobject *, const struct attribute_group *);
 void sysfs_remove_group(struct kobject *, const struct attribute_group *);
 
+#else /* CONFIG_SYSFS */
+
+static inline int sysfs_create_dir(struct kobject * k)
+{
+	return 0;
+}
+
+static inline void sysfs_remove_dir(struct kobject * k)
+{
+	;
+}
+
+static inline void sysfs_rename_dir(struct kobject * k, const char *new_name)
+{
+	;
+}
+
+static inline int sysfs_create_file(struct kobject * k, const struct attribute * a)
+{
+	return 0;
+}
+
+static inline int sysfs_update_file(struct kobject * k, const struct attribute * a)
+{
+	return 0;
+}
+
+static inline void sysfs_remove_file(struct kobject * k, const struct attribute * a)
+{
+	;
+}
+
+static inline int sysfs_create_link(struct kobject * k, struct kobject * t, char * n)
+{
+	return 0;
+}
+
+static inline void sysfs_remove_link(struct kobject * k, char * name)
+{
+	;
+}
+
+
+static inline int sysfs_create_bin_file(struct kobject * k, struct bin_attribute * a)
+{
+	return 0;
+}
+
+static inline int sysfs_remove_bin_file(struct kobject * k, struct bin_attribute * a)
+{
+	return 0;
+}
+
+static inline int sysfs_create_group(struct kobject * k, const struct attribute_group *g)
+{
+	return 0;
+}
+
+static inline void sysfs_remove_group(struct kobject * k, const struct attribute_group * g)
+{
+	;
+}
+
+#endif /* CONFIG_SYSFS */
+
 #endif /* _SYSFS_H_ */

init/do_mounts.c

@@ -141,9 +141,11 @@ dev_t __init name_to_dev_t(char *name)
 	dev_t res = 0;
 	int part;
 
+#ifdef CONFIG_SYSFS
 	sys_mkdir("/sys", 0700);
 	if (sys_mount("sysfs", "/sys", "sysfs", 0, NULL) < 0)
 		goto out;
+#endif
 
 	if (strncmp(name, "/dev/", 5) != 0) {
 		unsigned maj, min;