• 模块如何访问内核子系统VFS的某个static链表变量？

    模块如何访问内核子系统VFS的某个static链表变量？

    想法: 想要得到目前所有在VFS中注册过的文件系统，并且得到某个文件系统instance的super_block. 以及其自己实现的super_block.

    其实cat /proc/filesystems就能查看当前在kernel中已经注册的文件系统. 通过get_fs_type()可以拿到一个文件系统的file_system_type.但是我想要所有的fs type.

    思路：

    因为VFS通过一个非入侵式的list来存放所有已注册的文件系统,位于fs/filesystems.c中.

    该list是static的,那么不妨添加一个non-static函数将其暴露出来.然后使用EXPORT_SYMBOL()导出给模块使用.

    还有一点需要知道的是: 当某个文件系统mount后, VFS会将其该类型的所有挂载上的实例(super_block)都加入到struct file_system_type的fs_supers成员. fs_supers是一个hlist

    步骤:

    1. 在fs/filesystems.c文件下添加函数

      struct file_system_type *LuChao_getfilesystems() {
        return file_systems;
}
EXPORT_SYMBOL(LuChao_getfilesystems);

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    2. 在include/linux/fs.h中添加函数声明

      extern struct file_system_type *LuChao_getfilesystems(void);

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    3. 回到kernel的根目录下编译

      make然后make install

    4. 重新制作启动项然后重启(非UEFI)

      sudo grub2-mkconfig -o /boot/grub2/grub.cfg

    5. 查看是否成功导出符号

      cat /proc/kallsyms | grep LuChao

      [root@localhost linux]# cat /proc/kallsyms | grep LuChao
      ffffffffa50bcb40 T LuChao_getfilesystems
      ffffffffa5f5ebc8 r __ksymtab_LuChao_getfilesystems
      ffffffffa5f852ab r __kstrtab_LuChao_getfilesystems

    6. 最后就是编写一个模块来得到fs instance的super block对象. 以nova file system为例.

      懒得弄头文件包含路径,直接将super_block的定义拷贝过来用.

      super.h

      #ifndef __SUPER_H__
#define __SUPER_H__

/*
 *  * NOVA super-block data in DRAM
 *   */
struct nova_sb_info {
	struct super_block *sb;			/* VFS super block */
	struct nova_super_block *nova_sb;	/* DRAM copy of SB */
	struct block_device *s_bdev;
	struct dax_device *s_dax_dev;

	/*
	 *	 * base physical and virtual address of NOVA (which is also
	 *		 * the pointer to the super block)
	 *			 */
	phys_addr_t	phys_addr;
	void		*virt_addr;
	void		*replica_reserved_inodes_addr;
	void		*replica_sb_addr;

	unsigned long	num_blocks;

	/* TODO: Remove this, since it's unused */
	/*
	 *	 * Backing store option:
	 *		 * 1 = no load, 2 = no store,
	 *			 * else do both
	 *				 */
	unsigned int	nova_backing_option;

	/* Mount options */
	unsigned long	bpi;
	unsigned long	blocksize;
	unsigned long	initsize;
	unsigned long	s_mount_opt;
	kuid_t		uid;    /* Mount uid for root directory */
	kgid_t		gid;    /* Mount gid for root directory */
	umode_t		mode;   /* Mount mode for root directory */
	atomic_t	next_generation;
	/* inode tracking */
	unsigned long	s_inodes_used_count;
	unsigned long	head_reserved_blocks;
	unsigned long	tail_reserved_blocks;

	struct mutex	s_lock;	/* protects the SB's buffer-head */

	int cpus;
	struct proc_dir_entry *s_proc;

	/* Snapshot related */
	struct nova_inode_info	*snapshot_si;
	struct radix_tree_root	snapshot_info_tree;
	int num_snapshots;
	/* Current epoch. volatile guarantees visibility */
	volatile u64 s_epoch_id;
	volatile int snapshot_taking;

	int mount_snapshot;
	u64 mount_snapshot_epoch_id;

	struct task_struct *snapshot_cleaner_thread;
	wait_queue_head_t snapshot_cleaner_wait;
	wait_queue_head_t snapshot_mmap_wait;
	void *curr_clean_snapshot_info;

	/* DAX-mmap snapshot structures */
	struct mutex vma_mutex;
	struct list_head mmap_sih_list;

	/* ZEROED page for cache page initialized */
	void *zeroed_page;

	/* Checksum and parity for zero block */
	u32 zero_csum[8];
	void *zero_parity;

	/* Per-CPU journal lock */
	spinlock_t *journal_locks;

	/* Per-CPU inode map */
	struct inode_map	*inode_maps;

	/* Decide new inode map id */
	unsigned long map_id;

	/* Per-CPU free block list */
	struct free_list *free_lists;
	unsigned long per_list_blocks;
};

struct nova_super_block {
	/* static fields. they never change after file system creation.
	 *	 * checksum only validates up to s_start_dynamic field below
	 *		 */
	__le32		s_sum;			/* checksum of this sb */
	__le32		s_magic;		/* magic signature */
	__le32		s_padding32;
	__le32		s_blocksize;		/* blocksize in bytes */
	__le64		s_size;			/* total size of fs in bytes */
	char		s_volume_name[16];	/* volume name */

	/* all the dynamic fields should go here */
	__le64		s_epoch_id;		/* Epoch ID */

	/* s_mtime and s_wtime should be together and their order should not be
	 *	 * changed. we use an 8 byte write to update both of them atomically
	 *		 */
	__le32		s_mtime;		/* mount time */
	__le32		s_wtime;		/* write time */

	/* Metadata and data protections */
	u8		s_padding8;
	u8		s_metadata_csum;
	u8		s_data_csum;
	u8		s_data_parity;
} __attribute((__packed__));

#endif

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      模块中实现的代码部分: 比如拿到nova fs的超级块实际所在的kernel space的起始地址.

      struct file_system_type *cur = LuChao_getfilesystems();
struct nova_sb_info *sbi;
while (cur) {
	const char *name = cur->name;
	const char *module_name = cur->owner->name;
	
	if (!strncmp(name, NOVASTR, sizeof(NOVASTR)))
	{
		pr_info(DBG "[fs_name = %s\tfs'module_name = %s\tfs_description = %s]", name, module_name, cur->parameters->name);
		// traverse hlist of instance
		struct hlist_node *pinstances = cur->fs_supers.first;
		// get fs instance's super block
		struct super_block *sb = container_of(pinstances, struct super_block, s_instances);
		// get fs instance's implement super block
		sbi = (struct nova_sb_info *)sb->s_fs_info;
		break;
	}
	cur = cur->next;
}
// testing sbi
pr_info("nvmm phys_addr = %llx", (unsigned long long)sbi->phys_addr);
struct nova_super_block *nova_sb = sbi->nova_sb;
//pr_info("nova_sb. s_mtime = %lu, nova_sb.s_wtime = %lu", nova_sb->s_mtime, nova_sb->s_wtime);

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  • 原文地址：https://blog.csdn.net/qq_43580151/article/details/133278618