initial commit

this is a simple try of unuseful code in kernel space, debugfs is
used to create a dir and a file

5 files changed, 186 insertions, 0 deletions

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..4104b64
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,23 @@
+#ccflags-y += -g
+
+# Makfile assignments:
+#  := value at right is expanded and assigned at declaration time
+#   = value at right is expanded only when it is used, hence it is a reference
+#  ?= value at right is assigned only if the variable doesn't have a value
+#
+#
+
+# objects that are part of hello module (hello.o)
+hello-y += main.o debug.o
+
+# .ko module to be created
+obj-m := hello.o
+
+# '-C' changes the dir
+# '-M' causes the the kernel's toplevel Makefile to move back into this dir
+#      before trying to build 'modules' target
+all:
+	make -C /lib/modules/$(shell uname -r)/build KCPPFLAGS="-I$(CURDIR)" M=$(PWD) modules
+
+clean:
+	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
diff --git a/debug.c b/debug.c
new file mode 100644
index 0000000..40ee10c
--- /dev/null
+++ b/debug.c
@@ -0,0 +1,100 @@
+/*
+ * debug.c
+ *
+ * utilize debufs
+ * FIXME: R/W from /sys/kernel/debug/hello/magic doesn't work
+ *
+ */
+
+#include <linux/debugfs.h>
+#include <linux/types.h>
+#include <linux/errno.h>
+
+#include <debug.h>
+#include <main.h>
+
+#define BUFF_LEN 256
+char kernel_buff[BUFF_LEN] = {'f','o','o','b','a','r','\0'};
+
+/* debugfs_create_file's 4th param
+ * @data: a pointer to something that the caller will want to get to later
+ *        on.  The inode.i_private pointer will point to this value on
+ *        the open() call.
+ */
+int fileprv = 1; /* hmm */
+
+/* struct file, an abstract open file, not on disk, which would be a an inode */
+static ssize_t debugfs_read(struct file *fp, char __user /* userspace */ *ubuff, size_t c, loff_t *pos)
+{
+    /**
+     * simple_read_from_buffer - copy data from the buffer to user space
+     * @to: the user space buffer to read to
+     * @count: the maximum number of bytes to read
+     * @ppos: the current position in the buffer
+     * @from: the buffer to read from
+     * @available: the size of the buffer
+     *
+     * The simple_read_from_buffer() function reads up to @count bytes from the
+     * buffer @from at offset @ppos into the user space address starting at @to.
+     *
+     * On success, the number of bytes read is returned and the offset @ppos is
+     * advanced by this number, or negative value is returned on error.
+     **/
+    return simple_read_from_buffer(ubuff, c, pos, kernel_buff, BUFF_LEN);
+}
+
+static ssize_t debugfs_write(struct file *fp, const char __user *ubuff, size_t c, loff_t *pos)
+{
+    /**
+     * simple_write_to_buffer - copy data from user space to the buffer
+     * @to: the buffer to write to
+     * @available: the size of the buffer
+     * @ppos: the current position in the buffer
+     * @from: the user space buffer to read from
+     * @count: the maximum number of bytes to read
+     *
+     * The simple_write_to_buffer() function reads up to @count bytes from the user
+     * space address starting at @from into the buffer @to at offset @ppos.
+     *
+     * On success, the number of bytes written is returned and the offset @ppos is
+     * advanced by this number, or negative value is returned on error.
+     **/
+
+    if (c > BUFF_LEN)
+        return (-EINVAL);
+
+    return simple_write_to_buffer(kernel_buff, BUFF_LEN, pos, ubuff, c);
+}
+
+int debug_init(struct dentry **dir, struct dentry **file)
+{
+    /* func ptrs that perform various operations on the device, in this case char device, well not even */
+    struct file_operations fops = {
+        .read = debugfs_read,
+        .write = debugfs_write
+    };
+    /* omitted fields are initialized to NULL */
+
+    *dir = debugfs_create_dir("hello", NULL);
+    if (!*dir)
+        return (-ENODEV);
+
+    /* regular file, read by user/group/other, write by user */
+    *file = debugfs_create_file("magic", S_IFREG | S_IRUGO | S_IWUSR, *dir, &fileprv, &fops);
+    if (!*file)
+        printk("debugfs: error creating file\n");
+
+    return 0;
+}
+
+int debug_destroy(struct dentry *dir, struct dentry *file)
+{
+    if (file)
+        debugfs_remove(file);
+
+    if (dir)
+        debugfs_remove(dir);
+
+    return 0;
+}
+
diff --git a/debug.h b/debug.h
new file mode 100644
index 0000000..1b973bf
--- /dev/null
+++ b/debug.h
@@ -0,0 +1,10 @@
+#ifndef _DEBUG_H_
+#define _DEBUG_H_
+
+struct dentry;
+
+int debug_init(struct dentry **, struct dentry **);
+int debug_destroy(struct dentry *, struct dentry *);
+
+#endif
+
diff --git a/main.c b/main.c
new file mode 100644
index 0000000..6a65f3c
--- /dev/null
+++ b/main.c
@@ -0,0 +1,46 @@
+#include <linux/module.h>
+#include <linux/version.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/string.h>
+/* used for kmalloc */
+#include <linux/slab.h>
+
+#include <debug.h>
+
+char *debugmsg = "Tesla coil is a hi freq transformer";
+struct dentry *debug_dir = NULL;
+struct dentry *debug_file = NULL;
+
+/* __init is a hint that the func is only used at initialization time, then module
+ * loader drops the function after module is loaded making its memory available for other uses
+ */
+static int __init hello_init(void)
+{
+    int err = 0;
+    char *msg = (char *) kmalloc_array(128, sizeof(char), GFP_KERNEL /* kernel ram */);
+
+    printk("module named hello inserted\n");
+    strcpy(msg, "photon is the energy carrier particle for EM waves within light spectrum");
+    printk("%s\n", msg);
+    kfree(msg);
+
+    /* modifies passed in ptrs */
+    err = debug_init(&debug_dir, &debug_file);
+    if (err)
+        printk("debugfs might not have been mounted\n");
+
+    return 0;
+}
+ 
+static void __exit hello_exit(void)
+{
+    debug_destroy(debug_dir, debug_file);
+    printk("module named hello removed\n");
+}
+
+module_init(hello_init);
+module_exit(hello_exit);
+
+MODULE_LICENSE("GPL");
+
diff --git a/main.h b/main.h
new file mode 100644
index 0000000..229e387
--- /dev/null
+++ b/main.h
@@ -0,0 +1,7 @@
+#ifndef _MAIN_H_
+#define _MAIN_H_
+
+extern char *debugmsg;
+
+#endif
+