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root/include/linux/pipe_fs_i.h

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INCLUDED FROM


#ifndef _LINUX_PIPE_FS_I_H
#define _LINUX_PIPE_FS_I_H

#define PIPEFS_MAGIC 0x50495045

#define PIPE_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 */

/**
 *      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
 *      @wait: reader/writer wait point in case of empty/full pipe
 *      @nrbufs: the number of non-empty pipe buffers in this pipe
 *      @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
 *      @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
 *      @inode: inode this pipe is attached to
 *      @bufs: the circular array of pipe buffers
 **/
struct pipe_inode_info {
        wait_queue_head_t wait;
        unsigned int nrbufs, curbuf;
        struct page *tmp_page;
        unsigned int readers;
        unsigned int writers;
        unsigned int waiting_writers;
        unsigned int r_counter;
        unsigned int w_counter;
        struct fasync_struct *fasync_readers;
        struct fasync_struct *fasync_writers;
        struct inode *inode;
        struct pipe_buffer bufs[PIPE_BUFFERS];
};

/*
 * 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 KM_USER0 atomic slot for
         * atomic maps, so you can't map more than one pipe_buffer at once
         * and you have to be careful if mapping another page as source
         * or destination for a copy (IOW, it has to use something else
         * than KM_USER0).
         */
        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

/* 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(struct inode * inode);
void free_pipe_info(struct inode * inode);
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 *);

#endif

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