How to insert a ramfs module into linux kernel - c

Question

I want to compile source code of a very simple file system--ramfs. But when I inserted the module into Linux kernel 3.10 I got a problem:
could not insert module myramfs.ko: Device or resource busy
I don't know which step I did wrong。The following is my code.
source code:ramfs
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/highmem.h>
#include <linux/time.h>
#include <linux/string.h>
#include <linux/backing-dev.h>
#include <linux/ramfs.h>
#include <linux/sched.h>
#include <linux/parser.h>
#include <linux/magic.h>
#include <linux/slab.h>
#include <asm/uaccess.h>
#define RAMFS_DEFAULT_MODE 0755
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/ramfs.h>
const struct address_space_operations ramfs_aops = {
.readpage = simple_readpage,
.write_begin = simple_write_begin,
.write_end = simple_write_end,
.set_page_dirty = __set_page_dirty_no_writeback,
};
const struct file_operations ramfs_file_operations = {
.read = do_sync_read,
.aio_read = generic_file_aio_read,
.write = do_sync_write,
.aio_write = generic_file_aio_write,
.mmap = generic_file_mmap,
.fsync = noop_fsync,
.splice_read = generic_file_splice_read,
.splice_write = generic_file_splice_write,
.llseek = generic_file_llseek,
};
const struct inode_operations ramfs_file_inode_operations = {
.setattr = simple_setattr,
.getattr = simple_getattr,
};
static const struct super_operations ramfs_ops;
static const struct inode_operations ramfs_dir_inode_operations;
static struct backing_dev_info ramfs_backing_dev_info = {
.name = "ramfs",
.ra_pages = 0, /* No readahead */
.capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK |
BDI_CAP_MAP_DIRECT | BDI_CAP_MAP_COPY |
BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP,
};
struct inode *ramfs_get_inode(struct super_block *sb,
const struct inode *dir, umode_t mode, dev_t dev)
{
struct inode * inode = new_inode(sb);
if (inode) {
inode->i_ino = get_next_ino();
inode_init_owner(inode, dir, mode);
inode->i_mapping->a_ops = &ramfs_aops;
inode->i_mapping->backing_dev_info = &ramfs_backing_dev_info;
mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
mapping_set_unevictable(inode->i_mapping);
inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
switch (mode & S_IFMT) {
default:
init_special_inode(inode, mode, dev);
break;
case S_IFREG:
inode->i_op = &ramfs_file_inode_operations;
inode->i_fop = &ramfs_file_operations;
break;
case S_IFDIR:
inode->i_op = &ramfs_dir_inode_operations;
inode->i_fop = &simple_dir_operations;
/* directory inodes start off with i_nlink == 2 (for "." entry) */
inc_nlink(inode);
break;
case S_IFLNK:
inode->i_op = &page_symlink_inode_operations;
break;
}
}
return inode;
}
/*
* File creation. Allocate an inode, and we're done..
*/
/* SMP-safe */
static int
ramfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
{
struct inode * inode = ramfs_get_inode(dir->i_sb, dir, mode, dev);
int error = -ENOSPC;
if (inode) {
d_instantiate(dentry, inode);
dget(dentry); /* Extra count - pin the dentry in core */
error = 0;
dir->i_mtime = dir->i_ctime = CURRENT_TIME;
}
return error;
}
static int ramfs_mkdir(struct inode * dir, struct dentry * dentry, umode_t mode)
{
int retval = ramfs_mknod(dir, dentry, mode | S_IFDIR, 0);
if (!retval)
inc_nlink(dir);
return retval;
}
static int ramfs_create(struct inode *dir, struct dentry *dentry, umode_t mode, bool excl)
{
return ramfs_mknod(dir, dentry, mode | S_IFREG, 0);
}
static int ramfs_symlink(struct inode * dir, struct dentry *dentry, const char * symname)
{
struct inode *inode;
int error = -ENOSPC;
inode = ramfs_get_inode(dir->i_sb, dir, S_IFLNK|S_IRWXUGO, 0);
if (inode) {
int l = strlen(symname)+1;
error = page_symlink(inode, symname, l);
if (!error) {
d_instantiate(dentry, inode);
dget(dentry);
dir->i_mtime = dir->i_ctime = CURRENT_TIME;
} else
iput(inode);
}
return error;
}
static const struct inode_operations ramfs_dir_inode_operations = {
.create = ramfs_create,
.lookup = simple_lookup,
.link = simple_link,
.unlink = simple_unlink,
.symlink = ramfs_symlink,
.mkdir = ramfs_mkdir,
.rmdir = simple_rmdir,
.mknod = ramfs_mknod,
.rename = simple_rename,
};
static const struct super_operations ramfs_ops = {
.statfs = simple_statfs,
.drop_inode = generic_delete_inode,
.show_options = generic_show_options,
};
struct ramfs_mount_opts {
umode_t mode;
};
enum {
Opt_mode,
Opt_err
};
static const match_table_t tokens = {
{Opt_mode, "mode=%o"},
{Opt_err, NULL}
};
struct ramfs_fs_info {
struct ramfs_mount_opts mount_opts;
};
static int ramfs_parse_options(char *data, struct ramfs_mount_opts *opts)
{
substring_t args[MAX_OPT_ARGS];
int option;
int token;
char *p;
opts->mode = RAMFS_DEFAULT_MODE;
while ((p = strsep(&data, ",")) != NULL) {
if (!*p)
continue;
token = match_token(p, tokens, args);
switch (token) {
case Opt_mode:
if (match_octal(&args[0], &option))
return -EINVAL;
opts->mode = option & S_IALLUGO;
break;
/*
* We might like to report bad mount options here;
* but traditionally ramfs has ignored all mount options,
* and as it is used as a !CONFIG_SHMEM simple substitute
* for tmpfs, better continue to ignore other mount options.
*/
}
}
return 0;
}
int ramfs_fill_super(struct super_block *sb, void *data, int silent)
{
struct ramfs_fs_info *fsi;
struct inode *inode;
int err;
save_mount_options(sb, data);
fsi = kzalloc(sizeof(struct ramfs_fs_info), GFP_KERNEL);
sb->s_fs_info = fsi;
if (!fsi)
return -ENOMEM;
err = ramfs_parse_options(data, &fsi->mount_opts);
if (err)
return err;
sb->s_maxbytes = MAX_LFS_FILESIZE;
sb->s_blocksize = PAGE_CACHE_SIZE;
sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
sb->s_magic = RAMFS_MAGIC;
sb->s_op = &ramfs_ops;
sb->s_time_gran = 1;
inode = ramfs_get_inode(sb, NULL, S_IFDIR | fsi->mount_opts.mode, 0);
sb->s_root = d_make_root(inode);
if (!sb->s_root)
return -ENOMEM;
return 0;
}
struct dentry *ramfs_mount(struct file_system_type *fs_type,
int flags, const char *dev_name, void *data)
{
return mount_nodev(fs_type, flags, data, ramfs_fill_super);
}
static struct dentry *rootfs_mount(struct file_system_type *fs_type,
int flags, const char *dev_name, void *data)
{
return mount_nodev(fs_type, flags|MS_NOUSER, data, ramfs_fill_super);
}
static void ramfs_kill_sb(struct super_block *sb)
{
kfree(sb->s_fs_info);
kill_litter_super(sb);
}
static struct file_system_type ramfs_fs_type = {
.name = "ramfs",
.mount = ramfs_mount,
.kill_sb = ramfs_kill_sb,
.fs_flags = FS_USERNS_MOUNT,
};
static struct file_system_type rootfs_fs_type = {
.name = "rootfs",
.mount = rootfs_mount,
.kill_sb = kill_litter_super,
};
int __init init_ramfs_fs(void)
{
return register_filesystem(&ramfs_fs_type);
}
module_init(init_ramfs_fs)
int __init init_rootfs(void)
{
int err;
err = bdi_init(&ramfs_backing_dev_info);
if (err)
return err;
err = register_filesystem(&rootfs_fs_type);
if (err)
bdi_destroy(&ramfs_backing_dev_info);
return err;
}
Makefile:
ifneq ($(KERNELRELEASE),)
obj-m := myramfs.o
else
KERNELDIR ?= /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)
default:
$(MAKE) -C $(KERNELDIR) M=$(PWD) modules
endif
clean:
rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions *.order *.symvers *.unsigned