linux下，pipe的容量的讨论与查看
时间：2016-07-12 23:37:04
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1、pipe的容量
2.6标准版本的linux内核，pipe缓冲区是64KB，尽管命令ulimit -a看到管道大小8块,缓冲区的大小不是4 k,因为内核动态分配最大16“缓冲条目”,乘64 k。这些限制是硬编码的
2、如何查看自己pc上的pipe多大
1）通过ulimit -a查看到 pipe size 一次原子写入为：512Bytes*8=4096Bytes
查看缓冲条目个数：cat /usr/src/kernels/3.10.0-327.el7.x86_64/include/linux/pipe_fs_i.h文件
所以我的pc下得pipe缓冲大小为：16*4096=65536Bytes
也就验证了man 7 pipe下的pipe capacity
3、pipe的内部组织方式
在 Linux 中，管道的实现并没有使用专门的数据结构，而是借助了文件系统的file结构和VFS的索引节点inode。通过将两个 file 结构指向同一个临时的 VFS 索引节点，而这个 VFS 索引节点又指向一个物理页面而实现的。
有两个 file 数据结构，但它们定义文件操作例程地址是不同的，其中一个是向管道中写入数据的例程地址，而另一个是从管道中读出数据的例程地址。这样，用户程序的系统调用仍然是通常的文件操作，而内核却利用这种抽象机制实现了管道这一特殊操作。
cat /usr/src/kernels/3.10.0-327.el7.x86_64/include/linux/pipe_fs_i.h文件
#ifndef _LINUX_PIPE_FS_I_H
#define _LINUX_PIPE_FS_I_H
#define PIPE_DEF_BUFFERS 16
#define PIPE_BUF_FLAG_LRU 0x01 /* page is on the LRU */
#define PIPE_BUF_FLAG_ATOMIC 0x02 /* was atomically mapped */
#define PIPE_BUF_FLAG_GIFT 0x04 /* page is a gift */
#define PIPE_BUF_FLAG_PACKET 0x08 /* read() as a packet */
/**
* struct pipe_buffer - a linux kernel pipe buffer
* @page: the page containing the data for the pipe buffer
* @offset: offset of data inside the @page
* @len: length of data inside the @page
* @ops: operations associated with this buffer. See @pipe_buf_operations.
* @flags: pipe buffer flags. See above.
* @private: private data owned by the ops.
**/
struct pipe_buffer {
struct page *page;
unsigned int offset, len;
const struct pipe_buf_operations *ops;
unsigned int flags;
unsigned long private;
};
/**
* struct pipe_inode_info - a linux kernel pipe
* @mutex: mutex protecting the whole thing
* @wait: reader/writer wait point in case of empty/full pipe
* @nrbufs: the number of non-empty pipe buffers in this pipe
* @buffers: total number of buffers (should be a power of 2)
* @curbuf: the current pipe buffer entry
* @tmp_page: cached released page
* @readers: number of current readers of this pipe
* @writers: number of current writers of this pipe
* @files: number of struct file refering this pipe (protected by ->i_lock)
* @waiting_writers: number of writers blocked waiting for room
* @r_counter: reader counter
* @w_counter: writer counter
* @fasync_readers: reader side fasync
* @fasync_writers: writer side fasync
* @bufs: the circular array of pipe buffers
**/
struct pipe_inode_info {
struct mutex mutex;
wait_queue_head_t wait;
unsigned int nrbufs, curbuf, buffers;
unsigned int readers;
unsigned int writers;
unsigned int files;
unsigned int waiting_writers;
unsigned int r_counter;
unsigned int w_counter;
struct page *tmp_page;
struct fasync_struct *fasync_readers;
struct fasync_struct *fasync_writers;
struct pipe_buffer *bufs;
};
/*
* Note on the nesting of these functions:
*
* ->confirm()
* ->steal()
* ...
* ->map()
* ...
* ->unmap()
*
* That is, ->map() must be called on a confirmed buffer,
* same goes for ->steal(). See below for the meaning of each
* operation. Also see kerneldoc in fs/pipe.c for the pipe
* and generic variants of these hooks.
*/
struct pipe_buf_operations {
/*
* This is set to 1, if the generic pipe read/write may coalesce
* data into an existing buffer. If this is set to 0, a new pipe
* page segment is always used for new data.
*/
int can_merge;
/*
* ->map() returns a virtual address mapping of the pipe buffer.
* The last integer flag reflects whether this should be an atomic
* mapping or not. The atomic map is faster, however you can‘t take
* page faults before calling ->unmap() again. So if you need to eg
* access user data through copy_to/from_user(), then you must get
* a non-atomic map. ->map() uses the kmap_atomic slot for
* atomic maps, you have to be careful if mapping another page as
* source or destination for a copy.
*/
void * (*map)(struct pipe_inode_info *, struct pipe_buffer *, int);
/*
* Undoes ->map(), finishes the virtual mapping of the pipe buffer.
*/
void (*unmap)(struct pipe_inode_info *, struct pipe_buffer *, void *);
/*
* ->confirm() verifies that the data in the pipe buffer is there
* and that the contents are good. If the pages in the pipe belong
* to a file system, we may need to wait for IO completion in this
* hook. Returns 0 for good, or a negative error value in case of
* error.
*/
int (*confirm)(struct pipe_inode_info *, struct pipe_buffer *);
/*
* When the contents of this pipe buffer has been completely
* consumed by a reader, ->release() is called.
*/
void (*release)(struct pipe_inode_info *, struct pipe_buffer *);
/*
* Attempt to take ownership of the pipe buffer and its contents.
* ->steal() returns 0 for success, in which case the contents
* of the pipe (the buf->page) is locked and now completely owned
* by the caller. The page may then be transferred to a different
* mapping, the most often used case is insertion into different
* file address space cache.
*/
int (*steal)(struct pipe_inode_info *, struct pipe_buffer *);
/*
* Get a reference to the pipe buffer.
*/
void (*get)(struct pipe_inode_info *, struct pipe_buffer *);
};
/* Differs from PIPE_BUF in that PIPE_SIZE is the length of the actual
memory allocation, whereas PIPE_BUF makes atomicity guarantees. */
#define PIPE_SIZE PAGE_SIZE
/* Pipe lock and unlock operations */
void pipe_lock(struct pipe_inode_info *);
void pipe_unlock(struct pipe_inode_info *);
void pipe_double_lock(struct pipe_inode_info *, struct pipe_inode_info *);
extern unsigned int pipe_max_size, pipe_min_size;
int pipe_proc_fn(struct ctl_table *, int, void __user *, size_t *, loff_t *);
/* Drop the inode semaphore and wait for a pipe event, atomically */
void pipe_wait(struct pipe_inode_info *pipe);
struct pipe_inode_info *alloc_pipe_info(void);
void free_pipe_info(struct pipe_inode_info *);
/* Generic pipe buffer ops functions */
void *generic_pipe_buf_map(struct pipe_inode_info *, struct pipe_buffer *, int);
void generic_pipe_buf_unmap(struct pipe_inode_info *, struct pipe_buffer *, void *);
void generic_pipe_buf_get(struct pipe_inode_info *, struct pipe_buffer *);
int generic_pipe_buf_confirm(struct pipe_inode_info *, struct pipe_buffer *);
int generic_pipe_buf_steal(struct pipe_inode_info *, struct pipe_buffer *);
void generic_pipe_buf_release(struct pipe_inode_info *, struct pipe_buffer *);
/* for F_SETPIPE_SZ and F_GETPIPE_SZ */
long pipe_fcntl(struct file *, unsigned int, unsigned long arg);
struct pipe_inode_info *get_pipe_info(struct file *file);
int create_pipe_files(struct file **, int);
#endif将上面的文件进行提取重要的结构
//inode结点信息结构
struct inode {
...
struct pipe_inode_info *i_pipe;
...
};
//管道缓冲区个数
#define PIPE_BUFFERS (16)
//管道缓存区对象结构
struct pipe_buffer {
struct page *page; //管道缓冲区页框的描述符地址
unsigned int offset, len; //页框内有效数据的当前位置，和有效数据的长度
struct pipe_buf_operations *ops; //管道缓存区方法表的地址
};
//管道信息结构
struct pipe_inode_info {
wait_queue_head_t wait; //管道等待队列
unsigned int nrbufs, curbuf;
//包含待读数据的缓冲区数和包含待读数据的第一个缓冲区的索引
struct pipe_buffer bufs[PIPE_BUFFERS]; //管道缓冲区描述符数组
struct page *tmp_page; //高速缓存区页框指针
unsigned int start; //当前管道缓存区读的位置
unsigned int readers; //读进程的标志，或编号
unsigned int writers; //写进程的标志，或编号
unsigned int waiting_writers; //在等待队列中睡眠的写进程的个数
unsigned int r_counter; //与readers类似，但当等待写入FIFO的进程是使用
unsigned int w_counter; //与writers类似，但当等待写入FIFO的进程时使用
struct fasync_struct *fasync_readers; //用于通过信号进行的异步I/O通知
struct fasync_struct *fasync_writers; //用于通过信号的异步I/O通知
};本文出自 “momo就是辣么萌” 博客，请务必保留此出处http://momo462.blog.51cto.com/10138434/1825852
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