1.sysf文件系统的全局变量

static struct vfsmount *sysfs_mount;struct super_block * sysfs_sb = NULL;struct kmem_cache *sysfs_dir_cachep;

2. 文件系统类型：file_system_type

fs/sysfs/symlink.c

static struct file_system_type sysfs_fs_type = {    .name        = "sysfs",    .get_sb        = sysfs_get_sb,    .kill_sb    = kill_anon_super,};

 2.sysfs文件系统初始化：sysfs_init

fs/sysfs/symlink.c

struct kmem_cache *sysfs_dir_cachep; int __init sysfs_init(void){    int err = -ENOMEM;     /*创建一个分配sysfs_dirent的cash, name :sysfs_dir_cache 此cashe在/proc/slabinfo中显示的名字*/    sysfs_dir_cachep = kmem_cache_create("sysfs_dir_cache", sizeof(struct sysfs_dirent), 0, 0, NULL);    if (!sysfs_dir_cachep)        goto out;    err = sysfs_inode_init();    if (err)        goto out_err;    err = register_filesystem(&sysfs_fs_type);    if (!err) {        sysfs_mount = kern_mount(&sysfs_fs_type);        if (IS_ERR(sysfs_mount)) {            printk(KERN_ERR "sysfs: could not mount!\n");            err = PTR_ERR(sysfs_mount);            sysfs_mount = NULL;            unregister_filesystem(&sysfs_fs_type);            goto out_err;        }    } else        goto out_err;out:    return err;out_err:    kmem_cache_destroy(sysfs_dir_cachep);    sysfs_dir_cachep = NULL;    goto out;}

  sysfs_inode_init():主要是初始化BDI（backing device infor ）信息

static struct backing_dev_info sysfs_backing_dev_info = {    .ra_pages    = 0,    /* No readahead */    .capabilities    = BDI_CAP_NO_ACCT_AND_WRITEBACK,};int __init sysfs_inode_init(void){    return bdi_init(&sysfs_backing_dev_info);}int bdi_init(struct backing_dev_info *bdi){    int i;    int err;    bdi->dev = NULL;    bdi->min_ratio = 0;    bdi->max_ratio = 100;    bdi->max_prop_frac = PROP_FRAC_BASE;    for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {        err = percpu_counter_init(&bdi->bdi_stat[i], 0);        if (err)            goto err;    }    bdi->dirty_exceeded = 0;    err = prop_local_init_percpu(&bdi->completions);    if (err) {err:        while (i--)            percpu_counter_destroy(&bdi->bdi_stat[i]);    }    return err;}

  register_filesystem(&sysfs_fs_type);

static struct file_system_type sysfs_fs_type = {    .name        = "sysfs",    .get_sb        = sysfs_get_sb,    .kill_sb    = kill_anon_super,};static int sysfs_get_sb(struct file_system_type *fs_type,int flags, const char *dev_name, void *data, struct vfsmount *mnt){    return get_sb_single(fs_type, flags, data, sysfs_fill_super, mnt);}

说明：

1.register_filesystem只是把文件系统描述结构，插入系统全局链表中；在该文件系统被挂载（mount）到系统时，调用文件系统结构体的getsb函数，完成对文件系统的超级块分配和初始化；

2.get_sb_single函数创建一个新的super_block，并用sysfs_fill_super填充这个super_block结构，然后使mnt->mnt_sb指向该super_block,mnt->mnt_root指向该超级块的文件系统的根目录的

目录项对象；

 sysfs_mount = kern_mount(&sysfs_fs_type);

#define kern_mount(type) kern_mount_data(type, NULL)struct vfsmount *kern_mount_data(struct file_system_type *type, void *data){    return vfs_kern_mount(type, MS_KERNMOUNT, type->name, data);}struct vfsmount *vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void *data){    struct vfsmount *mnt;    char *secdata = NULL;    int error;    if (!type)return ERR_PTR(-ENODEV);    error = -ENOMEM;    mnt = alloc_vfsmnt(name);    if (!mnt)goto out;    if (data && !(type->fs_flags & FS_BINARY_MOUNTDATA)) {        secdata = alloc_secdata();        if (!secdata)            goto out_mnt;        error = security_sb_copy_data(data, secdata);        if (error)            goto out_free_secdata;    }    /*调用文件系统的超级块分配函数*/    error = type->get_sb(type, flags, name, data, mnt);    if (error < 0)        goto out_free_secdata;    BUG_ON(!mnt->mnt_sb);    error = security_sb_kern_mount(mnt->mnt_sb, flags, secdata);    if (error)         goto out_sb;    mnt->mnt_mountpoint = mnt->mnt_root; //指向文件系统安装点目录的dentry    mnt->mnt_parent = mnt;    up_write(&mnt->mnt_sb->s_umount);//安装文件系统卸载所用的信号量    free_secdata(secdata);    return mnt;out_sb:    dput(mnt->mnt_root);    deactivate_locked_super(mnt->mnt_sb);out_free_secdata:    free_secdata(secdata);out_mnt:    free_vfsmnt(mnt);out:    return ERR_PTR(error);}

sysfs_get_sb

static int sysfs_get_sb(struct file_system_type *fs_type,    int flags, const char *dev_name, void *data, struct vfsmount *mnt){    return get_sb_single(fs_type, flags, data, sysfs_fill_super, mnt);}int get_sb_single(struct file_system_type *fs_type, int flags, void *data,int (*fill_super)(struct super_block *, void *, int), struct vfsmount *mnt){    struct super_block *s;    int error;    s = sget(fs_type, compare_single, set_anon_super, NULL);    if (IS_ERR(s))        return PTR_ERR(s);    if (!s->s_root) {        s->s_flags = flags;        error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);        if (error) {            deactivate_locked_super(s);            return error;        }        s->s_flags |= MS_ACTIVE;    }    do_remount_sb(s, flags, data, 0);    simple_set_mnt(mnt, s);//系统挂载点指向超级块的根目录的dentry和超级块本身    return 0;} void simple_set_mnt(struct vfsmount *mnt, struct super_block *sb) {
        mnt->mnt_sb = sb;     mnt->mnt_root = dget(sb->s_root);//指向文件系统根目录的dentry }

超级块的填充

fs/sysfs/symlink.c line29 static const struct super_operations sysfs_ops = {
         .statfs        = simple_statfs,     .drop_inode    = generic_delete_inode,     .delete_inode    = sysfs_delete_inode, }; static int sysfs_fill_super(struct super_block *sb, void *data, int silent){    struct inode *inode;    struct dentry *root;    sb->s_blocksize = PAGE_CACHE_SIZE;      //块的大小，以字节为单位    sb->s_blocksize_bits = PAGE_CACHE_SHIFT;//基本块设备驱动程序中块的大小，以字节为单位    sb->s_magic = SYSFS_MAGIC; //文件系统的魔数    sb->s_op = &sysfs_ops;    sb->s_time_gran = 1;    sysfs_sb = sb;    /* get root inode, initialize and unlock it */    mutex_lock(&sysfs_mutex);    inode = sysfs_get_inode(&sysfs_root);    mutex_unlock(&sysfs_mutex);    if (!inode) {        pr_debug("sysfs: could not get root inode\n");        return -ENOMEM;    }    /* instantiate and link root dentry */    root = d_alloc_root(inode);    if (!root) {        pr_debug("%s: could not get root dentry!\n",__func__);        iput(inode);        return -ENOMEM;    }    root->d_fsdata = &sysfs_root;    sb->s_root = root;    return 0;}