Linux+26179内核文件系统调用详解.doc

Linux 2.6.17.9内核文件系统调用详解本部分主要讲述的是文件I/O操作的2.6.17.9内核版本实现，包括了主要的数据结构、宏定义和函数流程。以下分别讲述open，create，close，read，write，lseek系统调用。1 重要数据结构1.1 struct filestruct file /* * fu_list becomes invalid after file_free is called and queued via * fu_rcuhead for RCU freeing */ union struct list_head fu_list; /文件链表指针 struct rcu_head fu_rcuhead; /rcu链表 f_u; struct dentry *f_dentry; / 文件对应的目录结构 struct vfsmount *f_vfsmnt; / 虚拟文件系统挂载点 const struct file_operations *f_op; / 文件操作函数指针 atomic_t f_count; / 引用计数 unsigned int f_flags; mode_t f_mode; / 文件模式 loff_t f_pos; / 文件offset struct fown_struct f_owner; /文件owner 结构 unsigned int f_uid, f_gid;/文件用户id，组id struct file_ra_state f_ra; / 跟踪上次文件操作状态的结构指针 unsigned long f_version; void *f_security; / hook 文件操作的security结构指针 /* needed for tty driver, and maybe others */ void *private_data; / tty 驱动器所需数据#ifdef CONFIG_EPOLL /* Used by fs/eventpoll.c to link all the hooks to this file */ struct list_head f_ep_links; / EPOLL 机制检测所需链表结构 spinlock_t f_ep_lock; / 兼容早期gcc bug 的标志#endif /* #ifdef CONFIG_EPOLL */ struct address_space *f_mapping; / 地址映射表;1.2 struct fown_structstruct fown_struct rwlock_t lock; /* protects pid, uid, euid fields */ int pid; /* pid or -pgrp where SIGIO should be sent */ uid_t uid, euid; /* uid/euid of process setting the owner */ void *security; /*hook 文件操作的security结构指针*/ int signum; /* posix.1b rt signal to be delivered on IO */;1.3 struct file_ra_state/* Track a single files readahead state*/struct file_ra_state unsigned long start; /* Current window */ unsigned long size; unsigned long flags; /* ra flags RA_FLAG_xxx*/ unsigned long cache_hit; /* cache hit count*/ unsigned long prev_page; /* Cache last read() position */ unsigned long ahead_start; /* Ahead window */ unsigned long ahead_size; unsigned long ra_pages; /* Maximum readahead window */ unsigned long mmap_hit; /* Cache hit stat for mmap accesses */ unsigned long mmap_miss; /* Cache miss stat for mmap accesses */;1.4 struct address_spacestruct address_space struct inode *host; /* owner: inode, block_device */ struct radix_tree_root page_tree; /* radix tree of all pages */ rwlock_t tree_lock; /* and rwlock protecting it */ unsigned int i_mmap_writable;/* count VM_SHARED mappings */ struct prio_tree_root i_mmap; /* tree of private and shared mappings */ struct list_head i_mmap_nonlinear;/*list VM_NONLINEAR mappings */ spinlock_t i_mmap_lock; /* protect tree, count, list */ unsigned int truncate_count; /* Cover race condition with truncate */ unsigned long nrpages; /* number of total pages */ pgoff_t writeback_index;/* writeback starts here */ struct address_space_operations *a_ops; /* methods */ unsigned long flags; /* error bits/gfp mask */ struct backing_dev_info *backing_dev_info; /* device readahead, etc */ spinlock_t private_lock; /* for use by the address_space */ struct list_head private_list; /* ditto */ struct address_space *assoc_mapping; /* ditto */ _attribute_(aligned(sizeof(long);struct address_space_operations int (*writepage)(struct page *page, struct writeback_control *wbc); int (*readpage)(struct file *, struct page *); void (*sync_page)(struct page *); /* Write back some dirty pages from this mapping. */ int (*writepages)(struct address_space *, struct writeback_control *); /* Set a page dirty. Return true if this dirtied it */ int (*set_page_dirty)(struct page *page); int (*readpages)(struct file *filp, struct address_space *mapping, struct list_head *pages, unsigned nr_pages); /* * ext3 requires that a successful prepare_write() call be followed * by a commit_write() call - they must be balanced */ int (*prepare_write)(struct file *, struct page *, unsigned, unsigned); int (*commit_write)(struct file *, struct page *, unsigned, unsigned); /* Unfortunately this kludge is needed for FIBMAP. Dont use it */ sector_t (*bmap)(struct address_space *, sector_t); void (*invalidatepage) (struct page *, unsigned long); int (*releasepage) (struct page *, gfp_t); ssize_t (*direct_IO)(int, struct kiocb *, const struct iovec *iov, loff_t offset, unsigned long nr_segs); struct page* (*get_xip_page)(struct address_space *, sector_t, int); /* migrate the contents of a page to the specified target */ int (*migratepage) (struct page *, struct page *);1.5 struct block_devicestruct block_device dev_t bd_dev; /* not a kdev_t - its a search key */ struct inode * bd_inode; /* will die */ int bd_openers; struct mutex bd_mutex; /* open/close mutex */ struct mutex bd_mount_mutex; /* mount mutex */ struct list_head bd_inodes; void * bd_holder; int bd_holders;#ifdef CONFIG_SYSFS struct list_head bd_holder_list;#endif struct block_device * bd_contains; unsigned bd_block_size; struct hd_struct * bd_part; /* number of times partitions within this device have been opened. */ unsigned bd_part_count; int bd_invalidated; struct gendisk * bd_disk; struct list_head bd_list; struct backing_dev_info *bd_inode_backing_dev_info; /* * Private data. You must have bd_claimed the block_device * to use this. NOTE: bd_claim allows an owner to claim * the same device multiple times, the owner must take special * care to not mess up bd_private for that case. */ unsigned long bd_private;1.6 struct backing_dev_infostruct backing_dev_info unsigned long ra_pages; /* max readahead in PAGE_CACHE_SIZE units */ unsigned long state; /* Always use atomic bitops on this */ unsigned int capabilities; /* Device capabilities */ congested_fn *congested_fn; /* Function pointer if device is md/dm */ void *congested_data; /* Pointer to aux data for congested func */ void (*unplug_io_fn)(struct backing_dev_info *, struct page *); void *unplug_io_data;1.7 struct files_struct对于内核而言，所有打开文件都由文件描述符引用。文件描述符是一个非负整数。当打开一个现存文件或创建一个新文件时，内核向进程返回一个文件描述符。 当读、写一个文件时，用open或creat返回的文件描述符标识该文件，将其作为参数传送给read或write。在POSIX.1应用程序中，文件描述符为常数0、1和2分别代表STDIN_FILENO、STDOUT_FILENO和STDERR_FILENO，意即标准输入，标准输出和标准出错输出，这些常数都定义在头文件;中。 文件描述符的范围是0OPEN_MAX，在目前常用的linux系统中，是32位整形所能表示的整数，即65535，64位机上则更多。/* Open file table structure*/struct files_struct /* * read mostly part */ atomic_t count; /* 引用计数 */ struct fdtable *fdt; /* 文件表指针，指向fdtab */ struct fdtable fdtab;/* 文件表 *