include/linux/pipe_fs_i.h

   1 #ifndef _LINUX_PIPE_FS_I_H
   2 #define _LINUX_PIPE_FS_I_H
   3
   4 #define PIPEFS_MAGIC 0x50495045
   5
   6 #define PIPE_BUFFERS (16)
   7
   8 #define PIPE_BUF_FLAG_LRU       0x01    /* page is on the LRU */
   9 #define PIPE_BUF_FLAG_ATOMIC    0x02    /* was atomically mapped */
  10 #define PIPE_BUF_FLAG_GIFT      0x04    /* page is a gift */
  11
  12 /**
  13  *      struct pipe_buffer - a linux kernel pipe buffer
  14  *      @page: the page containing the data for the pipe buffer
  15  *      @offset: offset of data inside the @page
  16  *      @len: length of data inside the @page
  17  *      @ops: operations associated with this buffer. See @pipe_buf_operations.
  18  *      @flags: pipe buffer flags. See above.
  19  *      @private: private data owned by the ops.
  20  **/
  21 struct pipe_buffer {
  22         struct page *page;
  23         unsigned int offset, len;
  24         const struct pipe_buf_operations *ops;
  25         unsigned int flags;
  26         unsigned long private;
  27 };
  28
  29 /**
  30  *      struct pipe_inode_info - a linux kernel pipe
  31  *      @wait: reader/writer wait point in case of empty/full pipe
  32  *      @nrbufs: the number of non-empty pipe buffers in this pipe
  33  *      @curbuf: the current pipe buffer entry
  34  *      @tmp_page: cached released page
  35  *      @readers: number of current readers of this pipe
  36  *      @writers: number of current writers of this pipe
  37  *      @waiting_writers: number of writers blocked waiting for room
  38  *      @r_counter: reader counter
  39  *      @w_counter: writer counter
  40  *      @fasync_readers: reader side fasync
  41  *      @fasync_writers: writer side fasync
  42  *      @inode: inode this pipe is attached to
  43  *      @bufs: the circular array of pipe buffers
  44  **/
  45 struct pipe_inode_info {
  46         wait_queue_head_t wait;
  47         unsigned int nrbufs, curbuf;
  48         struct page *tmp_page;
  49         unsigned int readers;
  50         unsigned int writers;
  51         unsigned int waiting_writers;
  52         unsigned int r_counter;
  53         unsigned int w_counter;
  54         struct fasync_struct *fasync_readers;
  55         struct fasync_struct *fasync_writers;
  56         struct inode *inode;
  57         struct pipe_buffer bufs[PIPE_BUFFERS];
  58 };
  59
  60 /*
  61  * Note on the nesting of these functions:
  62  *
  63  * ->confirm()
  64  *      ->steal()
  65  *      ...
  66  *      ->map()
  67  *      ...
  68  *      ->unmap()
  69  *
  70  * That is, ->map() must be called on a confirmed buffer,
  71  * same goes for ->steal(). See below for the meaning of each
  72  * operation. Also see kerneldoc in fs/pipe.c for the pipe
  73  * and generic variants of these hooks.
  74  */
  75 struct pipe_buf_operations {
  76         /*
  77          * This is set to 1, if the generic pipe read/write may coalesce
  78          * data into an existing buffer. If this is set to 0, a new pipe
  79          * page segment is always used for new data.
  80          */
  81         int can_merge;
  82
  83         /*
  84          * ->map() returns a virtual address mapping of the pipe buffer.
  85          * The last integer flag reflects whether this should be an atomic
  86          * mapping or not. The atomic map is faster, however you can't take
  87          * page faults before calling ->unmap() again. So if you need to eg
  88          * access user data through copy_to/from_user(), then you must get
  89          * a non-atomic map. ->map() uses the KM_USER0 atomic slot for
  90          * atomic maps, so you can't map more than one pipe_buffer at once
  91          * and you have to be careful if mapping another page as source
  92          * or destination for a copy (IOW, it has to use something else
  93          * than KM_USER0).
  94          */
  95         void * (*map)(struct pipe_inode_info *, struct pipe_buffer *, int);
  96
  97         /*
  98          * Undoes ->map(), finishes the virtual mapping of the pipe buffer.
  99          */
 100         void (*unmap)(struct pipe_inode_info *, struct pipe_buffer *, void *);
 101
 102         /*
 103          * ->confirm() verifies that the data in the pipe buffer is there
 104          * and that the contents are good. If the pages in the pipe belong
 105          * to a file system, we may need to wait for IO completion in this
 106          * hook. Returns 0 for good, or a negative error value in case of
 107          * error.
 108          */
 109         int (*confirm)(struct pipe_inode_info *, struct pipe_buffer *);
 110
 111         /*
 112          * When the contents of this pipe buffer has been completely
 113          * consumed by a reader, ->release() is called.
 114          */
 115         void (*release)(struct pipe_inode_info *, struct pipe_buffer *);
 116
 117         /*
 118          * Attempt to take ownership of the pipe buffer and its contents.
 119          * ->steal() returns 0 for success, in which case the contents
 120          * of the pipe (the buf->page) is locked and now completely owned
 121          * by the caller. The page may then be transferred to a different
 122          * mapping, the most often used case is insertion into different
 123          * file address space cache.
 124          */
 125         int (*steal)(struct pipe_inode_info *, struct pipe_buffer *);
 126
 127         /*
 128          * Get a reference to the pipe buffer.
 129          */
 130         void (*get)(struct pipe_inode_info *, struct pipe_buffer *);
 131 };
 132
 133 /* Differs from PIPE_BUF in that PIPE_SIZE is the length of the actual
 134    memory allocation, whereas PIPE_BUF makes atomicity guarantees.  */
 135 #define PIPE_SIZE               PAGE_SIZE
 136
 137 /* Drop the inode semaphore and wait for a pipe event, atomically */
 138 void pipe_wait(struct pipe_inode_info *pipe);
 139
 140 struct pipe_inode_info * alloc_pipe_info(struct inode * inode);
 141 void free_pipe_info(struct inode * inode);
 142 void __free_pipe_info(struct pipe_inode_info *);
 143
 144 /* Generic pipe buffer ops functions */
 145 void *generic_pipe_buf_map(struct pipe_inode_info *, struct pipe_buffer *, int);
 146 void generic_pipe_buf_unmap(struct pipe_inode_info *, struct pipe_buffer *, void *);
 147 void generic_pipe_buf_get(struct pipe_inode_info *, struct pipe_buffer *);
 148 int generic_pipe_buf_confirm(struct pipe_inode_info *, struct pipe_buffer *);
 149 int generic_pipe_buf_steal(struct pipe_inode_info *, struct pipe_buffer *);
 150
 151 #endif