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說(shuō)明：本文基于Linux2.6內(nèi)核分析；其他內(nèi)核版本僅供參考,。 前邊通過(guò)源碼情景分析,，看過(guò)了總線、設(shè)備,、驅(qū)動(dòng)及其發(fā)現(xiàn)機(jī)制,，Linux2.6內(nèi)核udev設(shè)備節(jié)點(diǎn)創(chuàng)建相關(guān)；對(duì)于文件系統(tǒng),，一直望而生畏,，但內(nèi)核學(xué)習(xí)、這部分又不可能繞的過(guò)去,。目前對(duì)VFS中使用的hash表還未做研究,，它在dentry和vfsmount下查找節(jié)點(diǎn)起關(guān)鍵作用；后邊在做分析,。下邊將根文件系統(tǒng)掛載過(guò)程做簡(jiǎn)單分析： 一,、rootfs的誕生 引子： Linux一切皆文件的提出：在Linux中，普通文件,、目錄,、字符設(shè)備、塊設(shè)備,、套接字等都以文件被對(duì)待,；他們具體的類型及其操作不同,，但需要向上層提供統(tǒng)一的操作接口。 虛擬文件系統(tǒng)VFS就是Linux內(nèi)核中的一個(gè)軟件層,，向上給用戶空間程序提供文件系統(tǒng)操作接口,；向下允許不同的文件系統(tǒng)共存。所以,，所有實(shí)際文件系統(tǒng)都必須實(shí)現(xiàn)VFS的結(jié)構(gòu)封裝,。 矛盾的提出： Linux系統(tǒng)中任何文件系統(tǒng)的掛載必須滿足兩個(gè)條件：掛載點(diǎn)和文件系統(tǒng)。 直接掛載nfs或flash文件系統(tǒng)有如下兩個(gè)問(wèn)題必須解決： 1.誰(shuí)來(lái)提供掛載點(diǎn),？我們可以想象自己創(chuàng)建一個(gè)超級(jí)塊(包含目錄項(xiàng)和i節(jié)點(diǎn)),，這時(shí)掛載點(diǎn)不是就有了嗎；很可惜,，linux引入VFS(一切皆文件,所有類型文件系統(tǒng)必須提供一個(gè)VFS的軟件層,、以向上層提供統(tǒng)一接口)后該問(wèn)題不能這么解決，因?yàn)閽燧d點(diǎn)必須關(guān)聯(lián)到文件系統(tǒng),、也就是說(shuō)掛載點(diǎn)必須屬于某個(gè)文件系統(tǒng),。 2.怎樣訪問(wèn)到nfs或flash上的文件系統(tǒng)？我們可以說(shuō)直接訪問(wèn)設(shè)備驅(qū)動(dòng)讀取其上邊的文件系統(tǒng)（設(shè)備上的文件系統(tǒng)是掛載在自己的根目錄）,，不就可以了嗎,；別忘了還是Linux的VFS，設(shè)備訪問(wèn)也不例外,。因?yàn)樵L問(wèn)設(shè)備還是需要通過(guò)文件系統(tǒng)來(lái)訪問(wèn)它的掛載點(diǎn),，不能直接訪問(wèn)(要滿足Linux的VFS架構(gòu)，一切皆文件),。 所以,，一句話：rootfs之所以存在，是因?yàn)樾枰赩FS機(jī)制下給系統(tǒng)提供最原始的掛載點(diǎn),。 如此矛盾,，需要我們引入一種特殊文件系統(tǒng)： 1.它是系統(tǒng)自己創(chuàng)建并加載的第一個(gè)文件系統(tǒng)；該文件系統(tǒng)的掛載點(diǎn)就是它自己的根目錄項(xiàng),。 2.該文件系統(tǒng)不能存在于nfs或flash上,，因?yàn)槿绱藢?huì)陷入之前的矛盾。 rootfs的誕生： 上述問(wèn)題需要我們創(chuàng)建具有如下三個(gè)特點(diǎn)的特殊文件系統(tǒng)： 1.它是系統(tǒng)自己創(chuàng)建并加載的第一個(gè)文件系統(tǒng),； 2.該文件系統(tǒng)的掛載點(diǎn)就是它自己的根目錄項(xiàng)對(duì)象,； 3.該文件系統(tǒng)僅僅存在于內(nèi)存中。 由以上分析可以看出,，rootfs是Linux的VFS(一切皆文件,，所有類型文件系統(tǒng)必須提供一個(gè)VFS的軟件層、以向上層提供統(tǒng)一接口)存在的基石；二者關(guān)系密切,。如果沒有VFS機(jī)制,，rootfs也就沒有存在的必要；同樣,，如果沒有rootfs、VFS機(jī)制也就不能實(shí)現(xiàn)。 這就是兩者之間的真正關(guān)系,，之前看網(wǎng)上什么說(shuō)法都有：有的只說(shuō)關(guān)系密切,，沒有指明具體關(guān)系；有的干脆誤人子弟,，說(shuō)VFS就是rootfs,。 其實(shí)，VFS是一種機(jī)制,、是Linux下每一種文件系統(tǒng)（包括剛才說(shuō)的rootfs,，還有常見的ext3、yaffs等）都必須按照這個(gè)機(jī)制去實(shí)現(xiàn)的一種規(guī)范,；而rootfs僅僅是符合VFS規(guī)范的而且又具有如上3個(gè)特點(diǎn)的一個(gè)文件系統(tǒng),。 VFS是Linux文件系統(tǒng)實(shí)現(xiàn)必須遵循的一種機(jī)制，rootfs是一種具體實(shí)現(xiàn)的文件系統(tǒng),、Linux下所有文件系統(tǒng)的實(shí)現(xiàn)都必須符合VFS的機(jī)制(符合VFS的接口),；這就是二者的真正關(guān)系。 以下分析基于Android模擬器Linux2.6.29內(nèi)核： 二,、相關(guān)數(shù)據(jù)結(jié)構(gòu) Linux內(nèi)核中current指針作為全局變量,，使用非常廣泛；例如：進(jìn)程上下文中獲取當(dāng)前進(jìn)程ID,、任務(wù)調(diào)度,，以及open等文件系統(tǒng)調(diào)用中路徑搜索等；首先介紹下current結(jié)構(gòu)體： 各個(gè)平臺(tái),、各個(gè)內(nèi)核版本中current的實(shí)現(xiàn)可能不同,；但原理是一樣的。該指針一般定義在具體平臺(tái)的current.h頭文件中,，類型為struct task_struct： #define current (get_current()) static inline struct task_struct *get_current(void) include/linux/sched.h struct task_struct { ...... struct thread_info *thread_info; struct list_head tasks; pid_t pid; pid_t tgid; uid_t uid,euid,suid,fsuid; gid_t gid,egid,sgid,fsgid; struct fs_struct *fs; //本節(jié)將大量使用這個(gè) struct files_struct *files; ...... } 1.文件系統(tǒng)注冊(cè) kernel/include/include/fs.h struct file_system_type { const char *name; //文件系統(tǒng)名字；如:rootfs及ext3等 int fs_flags; int (*get_sb) (struct file_system_type *, int, const char *, void *, struct vfsmount *); //安裝/掛載文件系統(tǒng)時(shí),，會(huì)調(diào)用；獲取超級(jí)塊,。 void (*kill_sb) (struct super_block *); //卸載文件系統(tǒng)時(shí)會(huì)調(diào)用,。 struct module *owner; struct file_system_type * next; //指向下一個(gè)文件系統(tǒng)類型。 struct list_head fs_supers; //同一個(gè)文件系統(tǒng)類型中所有超級(jí)塊組成雙向鏈表,。 struct lock_class_key s_lock_key; struct lock_class_key s_umount_key; struct lock_class_key i_lock_key; struct lock_class_key i_mutex_key; struct lock_class_key i_mutex_dir_key; struct lock_class_key i_alloc_sem_key; }; 2.文件系統(tǒng)掛載vfsmount(struct vfsmount)： 本質(zhì)上,，mount操作的過(guò)程就是新建一個(gè)vfsmount結(jié)構(gòu)，然后將此結(jié)構(gòu)和掛載點(diǎn)(目錄項(xiàng)對(duì)象)關(guān)聯(lián),。關(guān)聯(lián)之后,，目錄查找時(shí)就能沿著vfsmount掛載點(diǎn)一級(jí)級(jí)向下查找文件了。 對(duì)于每一個(gè)mount的文件系統(tǒng),，都由一個(gè)vfsmount實(shí)例來(lái)表示,。 kernel/include/linux/mount.h struct vfsmount { struct list_head mnt_hash; //內(nèi)核通過(guò)哈希表對(duì)vfsmount進(jìn)行管理 struct vfsmount *mnt_parent;//指向父文件系統(tǒng)對(duì)應(yīng)的vfsmount struct dentry *mnt_mountpoint; //指向該文件系統(tǒng)掛載點(diǎn)對(duì)應(yīng)的目錄項(xiàng)對(duì)象dentry struct dentry *mnt_root; //該文件系統(tǒng)對(duì)應(yīng)的設(shè)備根目錄dentry struct super_block *mnt_sb; //指向該文件系統(tǒng)對(duì)應(yīng)的超級(jí)塊 struct list_head mnt_mounts; struct list_head mnt_child; //同一個(gè)父文件系統(tǒng)中的所有子文件系統(tǒng)通過(guò)該字段鏈接成雙聯(lián)表 int mnt_flags; /* 4 bytes hole on 64bits arches */ const char *mnt_devname;/* Name of device e.g. /dev/dsk/hda1 */ struct list_head mnt_list; //所有已掛載文件系統(tǒng)的vfsmount結(jié)構(gòu)通過(guò)該字段鏈接在一起 struct list_head mnt_expire;/* link in fs-specific expiry list */ struct list_head mnt_share;/* circular list of shared mounts */ struct list_head mnt_slave_list;/* list of slave mounts */ struct list_head mnt_slave;/* slave list entry */ struct vfsmount *mnt_master;/* slave is on master->mnt_slave_list */ struct mnt_namespace *mnt_ns;/* containing namespace */ int mnt_id;/* mount identifier */ int mnt_group_id;/* peer group identifier */ /* * We put mnt_count & mnt_expiry_mark at the end of struct vfsmount * to let these frequently modified fields in a separate cache line * (so that reads of mnt_flags wont ping-pong on SMP machines) */ atomic_t mnt_count; int mnt_expiry_mark;/* true if marked for expiry */ int mnt_pinned; int mnt_ghosts; /* * This value is not stable unless all of the mnt_writers[] spinlocks * are held, and all mnt_writer[]s on this mount have 0 as their ->count */ atomic_t __mnt_writers; }; 3.超級(jí)塊(struct super_bloc)： kernel/include/linux/fs.h struct super_block { struct list_heads_list;/* Keep this first */ dev_ts_dev;/* search index; _not_ kdev_t */ unsigned longs_blocksize; unsigned chars_blocksize_bits; unsigned chars_dirt; unsigned long longs_maxbytes;/* Max file size */ struct file_system_type*s_type; //文件系統(tǒng)類型 //(kernel/include/linux/fs.h,struct file_system_type) const struct super_operations*s_op; struct dquot_operations*dq_op; struct quotactl_ops*s_qcop; const struct export_operations *s_export_op; unsigned longs_flags; unsigned longs_magic; struct dentry*s_root; //超級(jí)塊要指向目錄項(xiàng)對(duì)象 struct rw_semaphores_umount; struct mutexs_lock; ints_count; ints_need_sync_fs; atomic_ts_active; #ifdef CONFIG_SECURITY void *s_security; #endif struct xattr_handler**s_xattr; struct list_heads_inodes;/* all inodes */ struct list_heads_dirty;/* dirty inodes */ struct list_heads_io;/* parked for writeback */ struct list_heads_more_io;/* parked for more writeback */ struct hlist_heads_anon;//哈希表頭/* anonymous dentries for (nfs) exporting */ struct list_heads_files; /* s_dentry_lru and s_nr_dentry_unused are protected by dcache_lock */ struct list_heads_dentry_lru;/* unused dentry lru */ ints_nr_dentry_unused;/* # of dentry on lru */ struct block_device*s_bdev; struct mtd_info*s_mtd; struct list_heads_instances; struct quota_infos_dquot;/* Diskquota specific options */ ints_frozen; wait_queue_head_ts_wait_unfrozen; char s_id[32];/* Informational name */ void *s_fs_info;/* Filesystem private info */ fmode_ts_mode; /* * The next field is for VFS *only*. No filesystems have any business * even looking at it. You had been warned. */ struct mutex s_vfs_rename_mutex;/* Kludge */ /* Granularity of c/m/atime in ns.Cannot be worse than a second */ u32 s_time_gran; /* * Filesystem subtype. If non-empty the filesystem type field * in /proc/mounts will be 'type.subtype' */ char *s_subtype; /* * Saved mount options for lazy filesystems using * generic_show_options() */ char *s_options; /* * storage for asynchronous operations */ struct list_head s_async_list; }; 4.目錄索引節(jié)點(diǎn)(struct inode)： kernel/include/linux/fs.h struct inode { struct hlist_nodei_hash; //哈希表節(jié)點(diǎn) struct list_headi_list; struct list_headi_sb_list; struct list_headi_dentry; unsigned longi_ino; atomic_ti_count; unsigned inti_nlink; uid_ti_uid; gid_ti_gid; dev_ti_rdev; u64i_version; loff_ti_size; #ifdef __NEED_I_SIZE_ORDERED seqcount_ti_size_seqcount; #endif struct timespeci_atime; struct timespeci_mtime; struct timespeci_ctime; unsigned inti_blkbits; blkcnt_ti_blocks; unsigned short i_bytes; umode_ti_mode; spinlock_ti_lock;/* i_blocks, i_bytes, maybe i_size */ struct mutexi_mutex; struct rw_semaphorei_alloc_sem; const struct inode_operations*i_op; const struct file_operations*i_fop;/* former ->i_op->default_file_ops */ struct super_block*i_sb; struct file_lock*i_flock; struct address_space*i_mapping; struct address_spacei_data; #ifdef CONFIG_QUOTA struct dquot*i_dquot[MAXQUOTAS]; #endif struct list_headi_devices; union { struct pipe_inode_info*i_pipe; struct block_device*i_bdev; struct cdev*i_cdev; }; inti_cindex; __u32i_generation; #ifdef CONFIG_DNOTIFY unsigned longi_dnotify_mask; /* Directory notify events */ struct dnotify_struct*i_dnotify; /* for directory notifications */ #endif #ifdef CONFIG_INOTIFY struct list_headinotify_watches; /* watches on this inode */ struct mutexinotify_mutex;/* protects the watches list */ #endif unsigned longi_state; unsigned longdirtied_when;/* jiffies of first dirtying */ unsigned inti_flags; atomic_ti_writecount; #ifdef CONFIG_SECURITY void*i_security; #endif void*i_private; /* fs or device private pointer */ }; 5.目錄項(xiàng)對(duì)象(struct dentry)： kernel/include/linux/dcache.h struct dentry { atomic_t d_count; unsigned int d_flags;/* protected by d_lock */ spinlock_t d_lock;/* per dentry lock */ int d_mounted; struct inode *d_inode; //目錄項(xiàng)對(duì)象與目錄索引的關(guān)聯(lián) /* Where the name belongs to - NULL is * negative */ /* * The next three fields are touched by __d_lookup. Place them here * so they all fit in a cache line. */ struct hlist_node d_hash; //哈希表節(jié)點(diǎn)/* lookup hash list */ struct dentry *d_parent; //目錄項(xiàng)對(duì)象的父親/* parent directory */ struct qstr d_name; //d_name.name這個(gè)是文件名,，目錄對(duì)象與目錄名的關(guān)聯(lián) struct list_head d_lru;/* LRU list */ /* * d_child and d_rcu can share memory */ union { struct list_head d_child;/* child of parent list */ struct rcu_head d_rcu; } d_u; struct list_head d_subdirs;/* our children */ struct list_head d_alias;/* inode alias list */ unsigned long d_time;/* used by d_revalidate */ struct dentry_operations *d_op; struct super_block *d_sb; //指向文件系統(tǒng)的超級(jí)塊/* The root of the dentry tree */ void *d_fsdata;/* fs-specific data */ unsigned char d_iname[DNAME_INLINE_LEN_MIN];/* small names */ }; 其他： include/linux/fs.h struct file { /* * fu_list becomes invalid after file_free is called and queued via * fu_rcuhead for RCU freeing */ union { struct list_headfu_list; struct rcu_head fu_rcuhead; } f_u; struct pathf_path; //重要?。?！記錄掛載信息和目錄項(xiàng)信息 #define f_dentryf_path.dentry #define f_vfsmntf_path.mnt const struct file_operations*f_op; atomic_long_tf_count; unsigned int f_flags; fmode_tf_mode; loff_tf_pos; struct fown_structf_owner; const struct cred*f_cred; struct file_ra_statef_ra; u64f_version; #ifdef CONFIG_SECURITY void*f_security; #endif /* needed for tty driver, and maybe others */ void*private_data; #ifdef CONFIG_EPOLL /* Used by fs/eventpoll.c to link all the hooks to this file */ struct list_headf_ep_links; spinlock_tf_ep_lock; #endif /* #ifdef CONFIG_EPOLL */ struct address_space*f_mapping; #ifdef CONFIG_DEBUG_WRITECOUNT unsigned long f_mnt_write_state; #endif }; include/linux/fs_struct.h struct fs_struct { atomic_t count; rwlock_t lock; int umask; struct path root, pwd; //重要?。?！記錄掛載信息和目錄項(xiàng)信息 }; include/linux/namei.h struct nameidata { struct pathpath; //重要?。?！記錄掛載信息和目錄項(xiàng)信息 struct qstrlast; //重要?。?！記錄目錄名 unsigned intflags; intlast_type; unsigneddepth; char *saved_names[MAX_NESTED_LINKS + 1]; /* Intent data */ union { struct open_intent open; } intent; }; include/linux/path.h struct path { struct vfsmount *mnt; //重要?。?！記錄文件系統(tǒng)掛載信息 struct dentry *dentry; //重要?。?！記錄目錄項(xiàng)信息 }; include/linux/dcache.h struct qstr { unsigned int hash; unsigned int len; const unsigned char *name;//重要?。?！目錄/文件名字,，如'/','tank1'等具體的文件名 }; 三、注冊(cè)/創(chuàng)建、安裝/掛載rootfs,，并調(diào)用set_fs_root設(shè)置系統(tǒng)current的根文件系統(tǒng)為rootfs 過(guò)程： 第一步：建立rootfs文件系統(tǒng),； 第二步：調(diào)用其get_sb函數(shù)(對(duì)于rootfs這種內(nèi)存/偽文件系統(tǒng)是get_sb_nodev，實(shí)際文件系統(tǒng)比如ext2等是get_sb_bdev),、建立超級(jí)塊(包含目錄項(xiàng)和i節(jié)點(diǎn)),； 第三步：掛載該文件系統(tǒng)(該文件系統(tǒng)的掛載點(diǎn)指向該文件系統(tǒng)超級(jí)塊的根目錄項(xiàng))； 第四步：將系統(tǒng)current的根文件系統(tǒng)和根目錄設(shè)置為rootfs和其根目錄,。 kernel/init/main.c asmlinkage void __init start_kernel(void) { setup_arch(&command_line);//解析uboot命令行,，實(shí)際文件系統(tǒng)掛載需要 parse_args('Booting kernel', static_command_line, __start___param, __stop___param - __start___param, &unknown_bootoption); vfs_caches_init(num_physpages); } kernel/fs/dcache.c void __init vfs_caches_init(unsigned long mempages) { mnt_init(); bdev_cache_init(); //塊設(shè)備文件創(chuàng)建 chrdev_init();//字符設(shè)備文件創(chuàng)建 } kernel/fs/namespace.c void __init mnt_init(void) { init_rootfs(); //向內(nèi)核注冊(cè)rootfs init_mount_tree();//重要！??！rootfs根目錄的建立以及rootfs文件系統(tǒng)的掛載；設(shè)置系統(tǒng)current根目錄和根文件系統(tǒng)為rootfs } 下邊分兩步： 1.向內(nèi)核注冊(cè)rootfs虛擬文件系統(tǒng)init_rootfs kernel/fs/ramfs/inode.cint __init init_rootfs(void) { err = register_filesystem(&rootfs_fs_type); } static struct file_system_type rootfs_fs_type = { .name= 'rootfs', .get_sb= rootfs_get_sb, .kill_sb= kill_litter_super, }; 2.建立rootfs的根目錄,，并將rootfs掛載到自己的根目錄；設(shè)置系統(tǒng)current根目錄和根文件系統(tǒng) kernel/fs/namespace.cstatic void __init init_mount_tree(void) { struct vfsmount *mnt; struct mnt_namespace *ns; struct path root; //創(chuàng)建rootfs的vfsmount結(jié)構(gòu),，建立rootfs的超級(jí)塊,、并將rootfs掛載到自己的根目錄。 /* mnt->mnt_mountpoint = mnt->mnt_root = dget(sb->s_root),，而該mnt和自己的sb是關(guān)聯(lián)的,； 所以，是把rootfs文件系統(tǒng)掛載到了自己對(duì)應(yīng)的超級(jí)塊的根目錄上,。 這里也是實(shí)現(xiàn)的關(guān)鍵：一般文件系統(tǒng)的掛載是調(diào)用do_mount->do_new_mount而該函數(shù)中首先調(diào)用do_kern_mount,，這時(shí)mnt->mnt_mountpoint = mnt->mnt_root；但后邊 它還會(huì)調(diào)用do_add_mount->graft_tree->attach_recursive_mnt如下代碼mnt_set_mountpoint(dest_mnt, dest_dentry, source_mnt)改變了其掛載點(diǎn)?。,。?br/> */ mnt = do_kern_mount('rootfs', 0, 'rootfs', NULL); list_add(&mnt->mnt_list, &ns->list); ns->root = mnt; //將創(chuàng)建好的mnt加入系統(tǒng)當(dāng)前 mnt->mnt_ns = ns; init_task.nsproxy->mnt_ns = ns; //設(shè)置進(jìn)程的命名空間 get_mnt_ns(ns); root.mnt = ns->root; //文件系統(tǒng)為rootfs,，相當(dāng)與root.mnt = mnt; root.dentry = ns->root->mnt_root;//目錄項(xiàng)為根目錄項(xiàng),，相當(dāng)與root.dentry = mnt->mnt_root; //設(shè)置系統(tǒng)current的pwd目錄和文件系統(tǒng) set_fs_pwd(current->fs, &root); //設(shè)置系統(tǒng)current根目錄,根文件系統(tǒng)。這個(gè)是關(guān)鍵?。,。≌麄€(gè)內(nèi)核代碼最多只有兩處調(diào)用 set_fs_root(current->fs, &root); } 以下著重分析do_kern_mount函數(shù),，它實(shí)現(xiàn)了rootfs在自己根目錄上的掛載： kernel/fs/super.cstruct vfsmount * do_kern_mount(const char *fstype, int flags, const char *name, void *data) { mnt = vfs_kern_mount(type, flags, name, data); return mnt; } kernel/fs/super.c struct vfsmount * vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void *data) { mnt = alloc_vfsmnt(name); //建立并填充vfsmount error = type->get_sb(type, flags, name, data, mnt);//為文件系統(tǒng)建立并填充超級(jí)塊(主要是其dentry和inode),，建立rootfs根目錄 mnt->mnt_mountpoint = mnt->mnt_root; //文件系統(tǒng)掛載點(diǎn)目錄,其實(shí)就是剛才建立的”/”目錄。掛載點(diǎn)就是自己?。,。。?br/> mnt->mnt_parent = mnt; //父對(duì)象是自己?。,。?！ return mnt; }kernel/fs/ramfs/inode.cstatic int rootfs_get_sb(struct file_system_type *fs_type, int flags, const char *dev_name, void *data, struct vfsmount *mnt) { return get_sb_nodev(fs_type, flags|MS_NOUSER, data, ramfs_fill_super, mnt); } kernel/fs/super.c int get_sb_nodev(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 = sget(fs_type, NULL, set_anon_super, NULL); //在內(nèi)存中分配一個(gè)超級(jí)塊 error = fill_super(s, data, flags & MS_SILENT ? 1 : 0); //執(zhí)行回調(diào),，填充超級(jí)塊，并建立根目錄項(xiàng)及對(duì)應(yīng)i節(jié)點(diǎn) /* kernel/fs/ramfs/inode.c static int ramfs_fill_super(struct super_block * sb, void * data, int silent) { struct inode * inode; struct dentry * root; 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; //static const struct super_operations ramfs_ops; sb->s_time_gran = 1; //建立根目錄索引節(jié)點(diǎn),，我們最終的目標(biāo)是要找到目錄項(xiàng)對(duì)象關(guān)聯(lián)的索引節(jié)點(diǎn),。 //根目錄索引節(jié)點(diǎn)會(huì)有自己的ops。 inode = ramfs_get_inode(sb, S_IFDIR | 0755, 0); //ramfs_get_inode kernel/fs/ramfs/inode.c struct inode *ramfs_get_inode(struct super_block *sb, int mode, dev_t dev) { struct inode * inode = new_inode(sb); switch (mode & S_IFMT) { //判斷文件類型 default: init_special_inode(inode, mode, dev); //init_special_inode void init_special_inode(struct inode *inode, umode_t mode, dev_t rdev) { inode->i_mode = mode; if (S_ISCHR(mode)) {//字符設(shè)備文件 inode->i_fop = &def_chr_fops; inode->i_rdev = rdev; } else if (S_ISBLK(mode)) {//塊設(shè)備文件 inode->i_fop = &def_blk_fops; inode->i_rdev = rdev; } else if (S_ISFIFO(mode)) inode->i_fop = &def_fifo_fops; else if (S_ISSOCK(mode)) //網(wǎng)絡(luò)設(shè)備文件 inode->i_fop = &bad_sock_fops; else printk(KERN_DEBUG 'init_special_inode: bogus i_mode (%o) for' ' inode %s:%lu\n', mode, inode->i_sb->s_id, inode->i_ino); } //init_special_inode end break; case S_IFREG: //普通文件 inode->i_op = &ramfs_file_inode_operations; //索引節(jié)點(diǎn)的操作方法 inode->i_fop = &ramfs_file_operations; //缺省普通文件的操作方法 break; case S_IFDIR: //目錄文件 inode->i_op = &ramfs_dir_inode_operations; //ramfs_dir_inode_operations static const struct inode_operations ramfs_dir_inode_operations; kernel/include/linux/fs.h struct inode_operations { int (*create) (struct inode *,struct dentry *,int, struct nameidata *); int (*mkdir) (struct inode *,struct dentry *,int); int (*rmdir) (struct inode *,struct dentry *); int (*mknod) (struct inode *,struct dentry *,int,dev_t); } //ramfs_dir_inode_operations end inode->i_fop = &simple_dir_operations; //目錄文件的操作方法 inc_nlink(inode); break; } } //ramfs_get_inode end //建立根目錄目錄對(duì)象,，目錄項(xiàng)對(duì)象的存在主要是為了我們進(jìn)行路徑的查找,。 root = d_alloc_root(inode); //d_alloc_root kernel/fs/dcache.c struct dentry * d_alloc_root(struct inode * root_inode) { struct dentry *res = NULL; static const struct qstr name = { .name = '/', .len = 1 }; res = d_alloc(NULL, &name); res->d_sb = root_inode->i_sb; //指向該文件系統(tǒng)的超級(jí)塊 res->d_parent = res; //根目錄的父親是它自己 d_instantiate(res, root_inode); //關(guān)聯(lián) dentry 和 inode } //d_alloc_root end sb->s_root = root; //超級(jí)塊的s_root指向剛建立的根目錄對(duì)象。 } */ return simple_set_mnt(mnt, s); //關(guān)聯(lián)超級(jí)塊(包含目錄項(xiàng)dentry和i節(jié)點(diǎn)inode)和vfsmount }kernel/fs/namespace.c int simple_set_mnt(struct vfsmount *mnt, struct super_block *sb) { printk('TK-------_>>>>>>>namespace.c>>>>simple_set_mnt\n');//add by tankai mnt->mnt_sb = sb; //對(duì) mnt_sb超級(jí)塊指針附值 mnt->mnt_root = dget(sb->s_root); //對(duì)mnt_root指向的根目錄賦值 return 0; } 至此,，rootfs文件系統(tǒng)建立,、并且掛載于自己超級(jí)塊(包括目錄項(xiàng)dentry和i節(jié)點(diǎn)inod)對(duì)應(yīng)的目錄項(xiàng)，設(shè)置了系統(tǒng)current根目錄和根文件系統(tǒng),、pwd的目錄和文件系統(tǒng),。 ======================================== 釋放Initramfs到rootfs；如果Initramfs中有init,，這種情況比較特殊,、rootfs就是最后系統(tǒng)使用的根文件系統(tǒng)。 而且此時(shí),，不需要在單獨(dú)燒錄根文件系統(tǒng)的img,；此時(shí)，根文件系統(tǒng)就是內(nèi)核uImage的一部分,。當(dāng)然,，缺陷就是該文件系統(tǒng)運(yùn)行時(shí)的介質(zhì)是ramdisk即內(nèi)存盤、它不再與磁盤對(duì)應(yīng),；因此,，此時(shí)修改根目錄下的文件將不被得到保存。它的內(nèi)核配置項(xiàng)為：CONFIG_INITRAMFS_SOURCE,。實(shí)際項(xiàng)目中會(huì)經(jīng)常碰到,。 make menuconfig->General setup->Initial RAM filesystem and RAM disk(initramfs/initrd) support 底下的Initramfs source file(s)填寫根文件系統(tǒng)的路徑，如：../out/target/product/tclm6/root,；不填的話,，將導(dǎo)致initrd或磁盤文件系統(tǒng)的掛載（因?yàn)橄逻厡?huì)看到，內(nèi)核將找不到“/init”）,。 對(duì)應(yīng)內(nèi)核源碼： kernel/init/main.cstatic int __init kernel_init(void * unused){ ...... do_basic_setup(); //初始化設(shè)備驅(qū)動(dòng),，加載靜態(tài)內(nèi)核模塊,；釋放Initramfs到rootfs /* kernel/init/initramfs.c rootfs_initcall(populate_rootfs); static int __init populate_rootfs(void) { printk(KERN_INFO 'checking if image is initramfs...'); err = unpack_to_rootfs((char *)initrd_start, initrd_end - initrd_start, 1); //釋放ramdisk到rootfs } */ ...... if (!ramdisk_execute_command) ramdisk_execute_command = '/init'; if (sys_access((const char __user *) ramdisk_execute_command, 0) != 0) { ramdisk_execute_command = NULL; //如果此時(shí)rootfs中沒有init，則加載initfd,、nfs或磁盤文件系統(tǒng) //也即磁盤的文件系統(tǒng)掛載至rootfs的/root目錄,，并設(shè)置系統(tǒng)current對(duì)應(yīng)的根目錄項(xiàng)為磁盤根目錄項(xiàng)、系統(tǒng)current根文件系統(tǒng)為磁盤文件系統(tǒng) //至此,，rootfs對(duì)于以后所有進(jìn)程而言,、已被隱藏。 prepare_namespace(); } init_post(); //啟動(dòng)init進(jìn)程 ...... } 看看init_post實(shí)現(xiàn)： static noinline int init_post(void) { if (ramdisk_execute_command) { //Initramfs從這里啟動(dòng)init run_init_process(ramdisk_execute_command); printk(KERN_WARNING 'Failed to execute %s\n', ramdisk_execute_command); } //initrd,、nfs和磁盤都是從如下啟動(dòng)的init if (execute_command) { run_init_process(execute_command); printk(KERN_WARNING 'Failed to execute %s. Attempting ' 'defaults...\n', execute_command); } //一般執(zhí)行如下 run_init_process('/sbin/init'); run_init_process('/etc/init'); run_init_process('/bin/init'); run_init_process('/bin/sh'); } 四,、掛載實(shí)際文件系統(tǒng)至rootfs，并調(diào)用set_fs_root設(shè)置為系統(tǒng)current的根文件系統(tǒng) 下邊從uboot啟動(dòng)內(nèi)核參數(shù)的角度來(lái)簡(jiǎn)單說(shuō)明： 以下三種情況都是將文件系統(tǒng)掛載到rootfs的/root目錄,，并將系統(tǒng)current的根目錄切換為/root,、系統(tǒng)current的根文件系統(tǒng)切換為磁盤文件系統(tǒng)。 kernel/init/do_mounts.c void __init prepare_namespace(void) { if (initrd_load()) //如果掛載initrd并執(zhí)行成功,，則不再掛載磁盤文件系統(tǒng) goto out; if (saved_root_name[0]) { root_device_name = saved_root_name; if (!strncmp(root_device_name, 'mtd', 3) || !strncmp(root_device_name, 'ubi', 3)) { mount_block_root(root_device_name, root_mountflags); //啟動(dòng)時(shí)root=參數(shù),，如《四.2》中“root=/dev/mtdblock0” goto out; } ROOT_DEV = name_to_dev_t(root_device_name); if (strncmp(root_device_name, '/dev/', 5) == 0) root_device_name += 5; } mount_root(); //將實(shí)際文件系統(tǒng)掛載到rootfs的/root目錄 out: //sys_mount('.', '/', NULL, MS_MOVE, NULL); 這句話無(wú)關(guān)緊要，影響理解,；屏蔽不影響功能 sys_chroot('.'); //將當(dāng)前目錄(/root)設(shè)置為系統(tǒng)current根目錄,，磁盤文件系統(tǒng)設(shè)置為系統(tǒng)current根文件系統(tǒng)。 } 下邊分兩步解釋mount_root()和sys_chroot('.')調(diào)用： 1.將nfs或磁盤文件系統(tǒng)掛載至rootfs的/root目錄（以磁盤為例） void __init mount_root(void) { if (mount_nfs_root()) //如果網(wǎng)絡(luò)文件系統(tǒng)掛載成功,，則nfs作為根文件系統(tǒng) return; //掛載磁盤文件系統(tǒng)為根文件系統(tǒng) //在rootfs中建立/dev/root設(shè)備文件 create_dev('/dev/root', ROOT_DEV); //在rootfs中建立/dev/root設(shè)備文件，也就是/dev/mtdblock0設(shè)備,。 //掛載/dev/root到rootfs的/root目錄 mount_block_root('/dev/root', root_mountflags); } void __init mount_block_root(char *name, int flags) { int err = do_mount_root(name, p, flags, root_mount_data); } static int __init do_mount_root(char *name, char *fs, int flags, void *data) { int err = sys_mount(name, '/root', fs, flags, data);//將/dev/root掛載到/root sys_chdir('/root'); //系統(tǒng)current->fs->pwd為當(dāng)前目錄/root ROOT_DEV = current->fs->pwd.mnt->mnt_sb->s_dev; return 0; } 2.將當(dāng)前目錄/root設(shè)置為系統(tǒng)current根目錄,，磁盤文件系統(tǒng)設(shè)置為系統(tǒng)current根文件系統(tǒng) 分析sys_chroot('.')：見Linux內(nèi)核編程之C語(yǔ)言預(yù)處理功能與宏 fs/open.c SYSCALL_DEFINE1(chroot, const char __user *, filename) { struct path path; error = user_path_dir(filename, &path); //這才是完成切換的關(guān)鍵！?。,。≌麄€(gè)內(nèi)核代碼只有兩處調(diào)用 set_fs_root(current->fs, &path); } 注意,，如下情況：rootfs特殊文件系統(tǒng)沒有被卸載,，他只是隱藏在基于磁盤的根文件系統(tǒng)下了。 initrd作為根文件系統(tǒng) setenv bootargs root=/dev/ram0 initrd=0x2800000,24M rootfstype=ext2 mem=64M console=ttyAMA0 參數(shù)說(shuō)明： root：用來(lái)指定rootfs的位置,。 rootfstype：用來(lái)指定文件系統(tǒng)的類型,。 nfs作為根文件系統(tǒng) setenv bootargs root=/dev/nfs nfsroot=192.168.1.7:/opt/yz/nfs,rw ip=192.168.1.160 mem=64M console=ttyAMA0 參數(shù)說(shuō)明： nfsroot：文件系統(tǒng)在哪臺(tái)主機(jī)的哪個(gè)目錄下。 ip：指定系統(tǒng)啟動(dòng)之后網(wǎng)卡的ip地址,。 flash作為根文件系統(tǒng) setenv bootargs root=/dev/mtdblock0 mem=16M mtdparts=armflash.1:4M@0x400000(jffs2) macaddr=9854 rootfstype=jffs2 console=ttyAMA0 參數(shù)說(shuō)明： mtdparts：根文件系統(tǒng)在flash中的位置,。 總結(jié)：rootfs永遠(yuǎn)不會(huì)被卸載，它只是被隱藏了,。在用戶空間下,，更多地情況是只能見到rootfs這棵大樹的一葉,，而且還是被安裝過(guò)文件系統(tǒng)了的。 五,、其他說(shuō)明 至于在mirco2440下mount出的結(jié)果： rootfs on / type rootfs (rw) /dev/root on / type yaffs (rw,relatime) none on /proc type proc (rw,relatime) none on /sys type sysfs (rw,relatime) none on /proc/bus/usb type usbfs (rw,relatime) none on /dev type ramfs (rw,relatime) none on /dev/pts type devpts (rw,relatime,mode=622) tmpfs on /dev/shm type tmpfs (rw,relatime) none on /tmp type ramfs (rw,relatime) none on /var type ramfs (rw,relatime) 從log中體會(huì)一下這個(gè)過(guò)程： s3c2410-rtc s3c2410-rtc: setting system clock to 2006-04-16 22:15:34 UTC (1145225734) TK------->>>>>init/main.c>>>>>>kernel_init>>before>prepare_namespace ################################################################################################################## TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_sb->s_type->name is rootfs ################################################################################################################## ################################################################################################################## TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_sb->s_type->name is rootfs ################################################################################################################## TK------->>>>>init/do_mounts.c>>>>>>prepare_namespace>>before>mount_root ################################################################################################################## TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_sb->s_type->name is rootfs ################################################################################################################## ################################################################################################################## TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_sb->s_type->name is rootfs ################################################################################################################## yaffs: dev is 32505859 name is 'mtdblock3' yaffs: passed flags '' yaffs: Attempting MTD mount on 31.3, 'mtdblock3' yaffs_read_super: isCheckpointed 0 VFS: Mounted root (yaffs filesystem) on device 31:3. TK------->>>>>init/do_mounts.c>>>>>>prepare_namespace>>before>sys_mount ################################################################################################################## TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_sb->s_type->name is rootfs ################################################################################################################## ################################################################################################################## TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_sb->s_type->name is yaffs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_name.name is root TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_sb->s_type->name is yaffs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_sb->s_type->name is yaffs ################################################################################################################## TK------->>>>>init/do_mounts.c>>>>>>prepare_namespace>>before>sys_chroot ################################################################################################################## TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_sb->s_type->name is rootfs ################################################################################################################## ################################################################################################################## TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_sb->s_type->name is yaffs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_name.name is root TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_sb->s_type->name is yaffs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_sb->s_type->name is yaffs ################################################################################################################## TK------->>>>>fs/open.c>>>>>>SYSCALL_DEFINE1(chroot>>before>set_fs_root ################################################################################################################## TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_sb->s_type->name is rootfs ################################################################################################################## ################################################################################################################## TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_sb->s_type->name is yaffs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_name.name is root TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_sb->s_type->name is yaffs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_sb->s_type->name is yaffs ################################################################################################################## TK------->>>>>init/do_mounts.c>>>>>>SYSCALL_DEFINE1(chroot>>after>set_fs_root ################################################################################################################## TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_sb->s_type->name is yaffs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_name.name is root TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_sb->s_type->name is yaffs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_sb->s_type->name is yaffs ################################################################################################################## ################################################################################################################## TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_sb->s_type->name is yaffs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_name.name is root TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_sb->s_type->name is yaffs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_sb->s_type->name is yaffs ################################################################################################################## TK------->>>>>init/do_mounts.c>>>>>>prepare_namespace>>after>sys_chroot ################################################################################################################## TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_sb->s_type->name is yaffs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_name.name is root TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_sb->s_type->name is yaffs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_sb->s_type->name is yaffs ################################################################################################################## ################################################################################################################## TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_sb->s_type->name is yaffs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_name.name is root TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_sb->s_type->name is yaffs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_sb->s_type->name is yaffs ################################################################################################################## TK------->>>>>init/main.c>>>>>>kernel_init>>after>prepare_namespace ################################################################################################################## TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_sb->s_type->name is yaffs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_name.name is root TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_sb->s_type->name is yaffs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_sb->s_type->name is yaffs ################################################################################################################## ################################################################################################################## TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_sb->s_type->name is yaffs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_name.name is root TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_sb->s_type->name is yaffs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_sb->s_type->name is yaffs ################################################################################################################## Freeing init memory: 156K [16/Apr/2006:14:15:35 +0000] boa: server version Boa/0.94.13 [16/Apr/2006:14:15:35 +0000] boa: server built Mar 26 2009 at 15:28:42. [16/Apr/2006:14:15:35 +0000] boa: starting server pid=681, port 80 Try to bring eth0 interface up......eth0: link down Done Please press Enter to activate this console. [root@FriendlyARM /]# mount rootfs on / type rootfs (rw) /dev/root on / type yaffs (rw,relatime) none on /proc type proc (rw,relatime) none on /sys type sysfs (rw,relatime) none on /proc/bus/usb type usbfs (rw,relatime) none on /dev type ramfs (rw,relatime) none on /dev/pts type devpts (rw,relatime,mode=622) tmpfs on /dev/shm type tmpfs (rw,relatime) none on /tmp type ramfs (rw,relatime) none on /var type ramfs (rw,relatime) [root@FriendlyARM /]# ubuntu下mount出的結(jié)果： /dev/sda5 on / type ext3 (rw,errors=remount-ro,commit=0) proc on /proc type proc (rw,noexec,nosuid,nodev) sysfs on /sys type sysfs (rw,noexec,nosuid,nodev) fusectl on /sys/fs/fuse/connections type fusectl (rw) none on /sys/kernel/debug type debugfs (rw) none on /sys/kernel/security type securityfs (rw) udev on /dev type devtmpfs (rw,mode=0755) devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620) tmpfs on /run type tmpfs (rw,noexec,nosuid,size=10%,mode=0755) none on /run/lock type tmpfs (rw,noexec,nosuid,nodev,size=5242880) none on /run/shm type tmpfs (rw,nosuid,nodev) /dev/sda7 on /home type ext3 (rw,commit=0) binfmt_misc on /proc/sys/fs/binfmt_misc type binfmt_misc (rw,noexec,nosuid,nodev) rpc_pipefs on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw) nfsd on /proc/fs/nfsd type nfsd (rw) gvfs-fuse-daemon on /home/tankai/.gvfs type fuse.gvfs-fuse-daemon (rw,nosuid,nodev,user=tankai) 一個(gè)還顯示rootfs,，一個(gè)干脆不顯示。這個(gè)無(wú)關(guān)緊要,?？赡躮icro2440中執(zhí)行mount命令還會(huì)將系統(tǒng)current根目錄的父節(jié)點(diǎn)也顯示出來(lái)；而ubuntu下不會(huì)再去關(guān)心系統(tǒng)current根目錄的父節(jié)點(diǎn),。但所有的文件搜索,，內(nèi)核都是從系統(tǒng)current根目錄開始向下查找的，因此,、可以說(shuō)我們不能在訪問(wèn)rootfs中除了作為系統(tǒng)current根文件系統(tǒng)之外的其他任何節(jié)點(diǎn),。 六、測(cè)試用例,，說(shuō)明系統(tǒng)current的文件系統(tǒng)布局,，不管在那個(gè)目錄、其根都不會(huì)改變： hello.c #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include //#include 'pnode.h' //#include 'internal.h' #include #include MODULE_LICENSE('Dual BSD/GPL'); static int hello_init(void) { printk(KERN_ALERT 'Hello, world\n'); printk('TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_name.name is %s\n',current->fs->root.dentry->d_name.name); printk('TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_sb->s_type->name is %s\n',current->fs->root.dentry->d_sb->s_type->name); printk('TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_name.name is %s\n',current->fs->root.mnt->mnt_mountpoint->d_name.name); printk('TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_sb->s_type->name is %s\n',current->fs->root.mnt->mnt_mountpoint->d_sb->s_type->name); printk('TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_name.name is %s\n',current->fs->root.mnt->mnt_root->d_name.name); printk('TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_sb->s_type->name is %s\n',current->fs->root.mnt->mnt_root->d_sb->s_type->name); printk('TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_sb->s_type->name is %s\n',current->fs->root.mnt->mnt_sb->s_type->name); printk('########################################################################################\n'); printk('TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_name.name is %s\n',current->fs->pwd.dentry->d_name.name); printk('TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_sb->s_type->name is %s\n',current->fs->pwd.dentry->d_sb->s_type->name); printk('TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_name.name is %s\n',current->fs->pwd.mnt->mnt_mountpoint->d_name.name); printk('TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_sb->s_type->name is %s\n',current->fs->pwd.mnt->mnt_mountpoint->d_sb->s_type->name); printk('TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_name.name is %s\n',current->fs->pwd.mnt->mnt_root->d_name.name); printk('TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_sb->s_type->name is %s\n',current->fs->pwd.mnt->mnt_root->d_sb->s_type->name); printk('TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_sb->s_type->name is %s\n',current->fs->pwd.mnt->mnt_sb->s_type->name); return 0; } static void hello_exit(void) { printk(KERN_ALERT'Goodbye, cruel world\n'); } module_init(hello_init); module_exit(hello_exit);Makefile ifneq ($(KERNELRELEASE),) obj-m:=hello.o else KERNELDIR:=/home/android2.3/android2.3_kernel/ PWD:=$(shell pwd) default: $(MAKE) -C $(KERNELDIR) M=$(PWD) modules clean: rm -rf *.o *.mod.c *.mod.o *.ko endif make生成hello.ko 先看下文件系統(tǒng)布局： mount rootfs / rootfs ro 0 0 tmpfs /dev tmpfs rw,mode=755 0 0 devpts /dev/pts devpts rw,mode=600 0 0 proc /proc proc rw 0 0 sysfs /sys sysfs rw 0 0 none /acct cgroup rw,cpuacct 0 0 tmpfs /mnt/asec tmpfs rw,mode=755,gid=1000 0 0 tmpfs /mnt/obb tmpfs rw,mode=755,gid=1000 0 0 none /dev/cpuctl cgroup rw,cpu 0 0 /dev/block/mtdblock0 /system yaffs2 rw 0 0 /dev/block/mtdblock1 /data yaffs2 rw,nosuid,nodev 0 0 /dev/block/mtdblock2 /cache yaffs2 rw,nosuid,nodev 0 0 /dev/block/vold/179:0 /mnt/sdcard vfat rw,dirsync,nosuid,nodev,noexec,uid=1000,gid=1015,fmask=0702,dmask=0702,allow_utime=0020,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0 /dev/block/vold/179:0 /mnt/secure/asec vfat rw,dirsync,nosuid,nodev,noexec,uid=1000,gid=1015,fmask=0702,dmask=0702,allow_utime=0020,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0 tmpfs /mnt/sdcard/.android_secure tmpfs ro,size=0k,mode=000 0 0 1.放入/data/下運(yùn)行insmod hello.ko rmmod hello.ko Hello, world TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_sb->s_type->name is rootfs ######################################################################################## TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_sb->s_type->name is yaffs2 TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_name.name is data TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_sb->s_type->name is yaffs2 TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_sb->s_type->name is yaffs2 Goodbye, cruel world2.放在/sdcard/tank/下運(yùn)行insmod hello.ko rmmod hello.koHello, world TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.dentry->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_mountpoint->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_root->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->root.mnt->mnt_sb->s_type->name is rootfs ######################################################################################## TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_name.name is tank TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.dentry->d_sb->s_type->name is vfat TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_name.name is sdcard TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_mountpoint->d_sb->s_type->name is rootfs TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_name.name is / TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_root->d_sb->s_type->name is vfat TK---->>>>init/main.c>>>kernel_init>>>>current->fs->pwd.mnt->mnt_sb->s_type->name is vfat Goodbye, cruel world 由此證明,；current->fs->root就是系統(tǒng)承認(rèn)的根文件系統(tǒng),。 |
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