rootfs注册挂载过程分析

init_rootfs();init_mount_tree();

init_rootfs() ???-->bdi_init(&ramfs_backing_dev_info); ???/* ???注册过程实际上将表示各实际文件系统的 struct file_system_type 数据结构的实例化， ???将rootfs_fs_type加入到static struct file_system_type *file_systems为首的单链表。 ???*/ ???-->register_filesystem(&rootfs_fs_type);

static struct backing_dev_info ramfs_backing_dev_info = { ???.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,};

init_mount_tree() ???-->struct vfsmount *mnt = do_kern_mount("rootfs", 0, "rootfs", NULL); ???????/* ???????1.根据“rootfs”在static struct file_system_type *file_systems链表中 ???????找到代表文件系统的file_system_type结构体 ???????*/ ???????-->struct file_system_type *type = get_fs_type("rootfs"); ???????-->struct vfsmount *mnt = vfs_kern_mount(type, 0, "rootfs", NULL); ???????????/*2.从mnt_cache缓存分配vfsmount结构体并初始化*/ ???????????-->struct vfsmount *mnt = alloc_vfsmnt(name); ???????????-->type->get_sb(type, 0, "rootfs", NULL, mnt); ???????????即rootfs_get_sb(type, 0, "rootfs", NULL, mnt); ???????????????-->get_sb_nodev(type, MS_NOUSER, NULL, ramfs_fill_super,mnt); ???????????????????-->struct super_block *s = sget(type, NULL, set_anon_super, NULL); ???????????????????????/*2.分配并初始化super_block结构体*/ ???????????????????????-->struct super_block *s = alloc_super(type); ???????????????????????-->set(s, NULL); ???????????????????????即set_anon_super(s,NULL) ???????????????????????????/*设置super_block结构体的s_dev成员*/ ???????????????????????????-->s->s_dev = MKDEV(0, dev & MINORMASK); ???????????????????????-->s->s_type = type; ???????????????????????-->strlcpy(s->s_id, type->name, sizeof(s->s_id)); ???????????????????????/*系统中所有的super_block结构体都连接到super_blocks为首的list_head链表*/ ???????????????????????-->list_add_tail(&s->s_list, &super_blocks); ???????????????????????/*属于file_system_type指定文件系统的super_block结构体都连接到type->fs_supers链表*/ ???????????????????????-->list_add(&s->s_instances, &type->fs_supers); ???????????????????-->s->s_flags = MS_NOUSER; ???????????????????-->fill_super(s, NULL, 0) ???????????????????即ramfs_fill_super(s, NULL, 0) ???????????????????????-->sb->s_op = &ramfs_ops; ???????????????????????/*3.分配inode结构体并初始化*/ ???????????????????????-->struct inode *inode = ramfs_get_inode(sb, S_IFDIR | fsi->mount_opts.mode, 0); ???????????????????????????-->struct inode * inode = new_inode(sb); ???????????????????????????-->设置inode成员 ???????????????????????/*4.分配dentry并初始化，“/”*/ ???????????????????????-->struct dentry *root = d_alloc_root(inode); ???????????????????????????-->static const struct qstr name = { .name = "/", .len = 1 } ???????????????????????????-->struct dentry *res = d_alloc(NULL, &name); ???????????????????????????-->res->d_sb = inode->i_sb; ???????????????????????????-->res->d_parent = res; ???????????????????????????-->d_instantiate(res, inode); ???????????????????????????????-->list_add(&res->d_alias, &inode->i_dentry); ???????????????????????????????-->res->d_inode = inode; ???????????????????-->s->s_flags |= MS_ACTIVE; ???????????????????-->simple_set_mnt(mnt, s); ???????????????????????-->mnt->mnt_sb = s; ???????????????????????-->mnt->mnt_root = dget(sb->s_root); ???????????mnt->mnt_mountpoint = mnt->mnt_root; ???????????mnt->mnt_parent = mnt; ???/* ???为系统最开始的进程(即 init_task 进程)准备它的进程数据块中的namespace 域， ???主要目的是将 do_kern_mount() 函数中建立的 mnt 和 dentry 信息记录在了 init_task 进程的进程数据块中， ???这样所有以后从 init_task 进程 fork 出来的进程也都先天地继承了这一信息 ???*/ ???-->struct mnt_namespace *ns = kmalloc(sizeof(*ns), GFP_KERNEL); ???-->list_add(&mnt->mnt_list, &ns->list); ???-->ns->root = mnt; ???-->mnt->mnt_ns = ns; ???-->struct path root.mnt = ns->root; ??????struct path root.dentry = ns->root->mnt_root; ???-->set_fs_pwd(current->fs, &root); ??????set_fs_root(current->fs, &root);

struct path { ???struct vfsmount *mnt; ???struct dentry *dentry;};/*这个数据结构在路径搜索的过程中用来记录相关信息，起着类似"路标"的作用其中前path.dentry记录的是要建目录的父目录的信息last,flags,last_type三项记录的是所查找路径的最后一个节点(即待建目录或文件)的信息。*/struct nameidata { ???struct path ???path; ???struct qstr ???last; ???unsigned int ???flags; ???int ???????last_type; ???unsigned ???depth; ???char *saved_names[MAX_NESTED_LINKS + 1]; ???/* Intent data */ ???union { ???????struct open_intent open; ???} intent;};

sys_mount("hda2","/dev ","ext2",…) ???/* ???将来自用户内存空间(user space)的参数拷贝到内核空间后， ???便调用 do_mount() 函数开始真正的安装文件系统的工作 ???*/ ???-->do_mount() ???????-->/*调用 path_lookup() 函数来得到安装点的相关信息， ???????如同创建目录过程中叙述的那样，该安装点的信息最终记录在 struct nameidata 类型的一个变量当中， ???????为叙述方便，记该变量为nd ???????*/ ???????/*调用 do_add_mount() 函数来向 VFS 树中安装点 "/dev " 安装一个实际的文件系统。*/ ???????-->do_add_mount() ???????????/*建立一新的安装区域块*/ ???????????-->do_kern_mount() ???????????-->graft_tree() ???????????????-->将 do_kern_mount() 函数返回的一 struct vfsmount 类型的变量加入到安装系统链表中 ???????????????-->将新分配的 struct vfsmount 类型的变量加入到一个hash表中