text: /*
   * linux/include/linux/relay.h
   *
   * Copyright (C) 2002, 2003 - Tom Zanussi (zanussi@us.ibm.com), IBM Corp
   * Copyright (C) 1999, 2000, 2001, 2002 - Karim Yaghmour (karim@opersys.com)
   *
   * CONFIG_RELAY definitions and declarations
   */
  
  #ifndef _LINUX_RELAY_H
  #define _LINUX_RELAY_H
  
  #include <linux/types.h>
  #include <linux/sched.h>
  #include <linux/timer.h>
  #include <linux/wait.h>
  #include <linux/list.h>
  #include <linux/fs.h>
  #include <linux/poll.h>
  #include <linux/kref.h>
  
  /* Needs a _much_ better name... */
  #define FIX_SIZE(x) ((((x) - 1) & PAGE_MASK) + PAGE_SIZE)
  
  /*
   * Tracks changes to rchan/rchan_buf structs
   */
  #define RELAYFS_CHANNEL_VERSION		7
  
  /*
   * Per-cpu relay channel buffer
   */
  struct rchan_buf
  {
  	void *start;			/* start of channel buffer */
  	void *data;			/* start of current sub-buffer */
  	size_t offset;			/* current offset into sub-buffer */
  	size_t subbufs_produced;	/* count of sub-buffers produced */
  	size_t subbufs_consumed;	/* count of sub-buffers consumed */
  	struct rchan *chan;		/* associated channel */
  	wait_queue_head_t read_wait;	/* reader wait queue */
  	struct timer_list timer; 	/* reader wake-up timer */
  	struct dentry *dentry;		/* channel file dentry */
  	struct kref kref;		/* channel buffer refcount */
  	struct page **page_array;	/* array of current buffer pages */
  	unsigned int page_count;	/* number of current buffer pages */
  	unsigned int finalized;		/* buffer has been finalized */
  	size_t *padding;		/* padding counts per sub-buffer */
  	size_t prev_padding;		/* temporary variable */
  	size_t bytes_consumed;		/* bytes consumed in cur read subbuf */
  	size_t early_bytes;		/* bytes consumed before VFS inited */
  	unsigned int cpu;		/* this buf's cpu */
  } ____cacheline_aligned;
  
  /*
   * Relay channel data structure
   */
  struct rchan
  {
  	u32 version;			/* the version of this struct */
  	size_t subbuf_size;		/* sub-buffer size */
  	size_t n_subbufs;		/* number of sub-buffers per buffer */
  	size_t alloc_size;		/* total buffer size allocated */
  	struct rchan_callbacks *cb;	/* client callbacks */
  	struct kref kref;		/* channel refcount */
  	void *private_data;		/* for user-defined data */
  	size_t last_toobig;		/* tried to log event > subbuf size */
  	struct rchan_buf *buf[NR_CPUS]; /* per-cpu channel buffers */
  	int is_global;			/* One global buffer ? */
  	struct list_head list;		/* for channel list */
  	struct dentry *parent;		/* parent dentry passed to open */
  	int has_base_filename;		/* has a filename associated? */
  	char base_filename[NAME_MAX];	/* saved base filename */
  };
  
  /*
   * Relay channel client callbacks
   */
  struct rchan_callbacks
  {
  	/*
  	 * subbuf_start - called on buffer-switch to a new sub-buffer
  	 * @buf: the channel buffer containing the new sub-buffer
  	 * @subbuf: the start of the new sub-buffer
  	 * @prev_subbuf: the start of the previous sub-buffer
  	 * @prev_padding: unused space at the end of previous sub-buffer
  	 *
  	 * The client should return 1 to continue logging, 0 to stop
  	 * logging.
  	 *
  	 * NOTE: subbuf_start will also be invoked when the buffer is
  	 *       created, so that the first sub-buffer can be initialized
  	 *       if necessary.  In this case, prev_subbuf will be NULL.
  	 *
  	 * NOTE: the client can reserve bytes at the beginning of the new
  	 *       sub-buffer by calling subbuf_start_reserve() in this callback.
  	 */
  	int (*subbuf_start) (struct rchan_buf *buf,
  			     void *subbuf,
  			     void *prev_subbuf,
  			     size_t prev_padding);
  
  	/*
  	 * buf_mapped - relay buffer mmap notification
  	 * @buf: the channel buffer
  	 * @filp: relay file pointer
  	 *
  	 * Called when a relay file is successfully mmapped
  	 */
          void (*buf_mapped)(struct rchan_buf *buf,
  			   struct file *filp);
  
  	/*
  	 * buf_unmapped - relay buffer unmap notification
  	 * @buf: the channel buffer
  	 * @filp: relay file pointer
  	 *
  	 * Called when a relay file is successfully unmapped
  	 */
          void (*buf_unmapped)(struct rchan_buf *buf,
  			     struct file *filp);
  	/*
  	 * create_buf_file - create file to represent a relay channel buffer
  	 * @filename: the name of the file to create
  	 * @parent: the parent of the file to create
  	 * @mode: the mode of the file to create
  	 * @buf: the channel buffer
  	 * @is_global: outparam - set non-zero if the buffer should be global
  	 *
  	 * Called during relay_open(), once for each per-cpu buffer,
  	 * to allow the client to create a file to be used to
  	 * represent the corresponding channel buffer.  If the file is
  	 * created outside of relay, the parent must also exist in
  	 * that filesystem.
  	 *
  	 * The callback should return the dentry of the file created
  	 * to represent the relay buffer.
  	 *
  	 * Setting the is_global outparam to a non-zero value will
  	 * cause relay_open() to create a single global buffer rather
  	 * than the default set of per-cpu buffers.
  	 *
  	 * See Documentation/filesystems/relay.txt for more info.
  	 */
  	struct dentry *(*create_buf_file)(const char *filename,
  					  struct dentry *parent,
  					  umode_t mode,
  					  struct rchan_buf *buf,
  					  int *is_global);
  
  	/*
  	 * remove_buf_file - remove file representing a relay channel buffer
  	 * @dentry: the dentry of the file to remove
  	 *
  	 * Called during relay_close(), once for each per-cpu buffer,
  	 * to allow the client to remove a file used to represent a
  	 * channel buffer.
  	 *
  	 * The callback should return 0 if successful, negative if not.
  	 */
  	int (*remove_buf_file)(struct dentry *dentry);
  };
  
  /*
   * CONFIG_RELAY kernel API, kernel/relay.c
   */
  
  struct rchan *relay_open(const char *base_filename,
  			 struct dentry *parent,
  			 size_t subbuf_size,
  			 size_t n_subbufs,
  			 struct rchan_callbacks *cb,
  			 void *private_data);
  extern int relay_late_setup_files(struct rchan *chan,
  				  const char *base_filename,
  				  struct dentry *parent);
  extern void relay_close(struct rchan *chan);
  extern void relay_flush(struct rchan *chan);
  extern void relay_subbufs_consumed(struct rchan *chan,
  				   unsigned int cpu,
  				   size_t consumed);
  extern void relay_reset(struct rchan *chan);
  extern int relay_buf_full(struct rchan_buf *buf);
  
  extern size_t relay_switch_subbuf(struct rchan_buf *buf,
  				  size_t length);
  
  /**
   *	relay_write - write data into the channel
   *	@chan: relay channel
   *	@data: data to be written
   *	@length: number of bytes to write
   *
   *	Writes data into the current cpu's channel buffer.
   *
   *	Protects the buffer by disabling interrupts.  Use this
   *	if you might be logging from interrupt context.  Try
   *	__relay_write() if you know you	won't be logging from
   *	interrupt context.
   */
  static inline void relay_write(struct rchan *chan,
  			       const void *data,
  			       size_t length)
  {
  	unsigned long flags;
  	struct rchan_buf *buf;
  
  	local_irq_save(flags);
  	buf = chan->buf[smp_processor_id()];
  	if (unlikely(buf->offset + length > chan->subbuf_size))
  		length = relay_switch_subbuf(buf, length);
  	memcpy(buf->data + buf->offset, data, length);
  	buf->offset += length;
  	local_irq_restore(flags);
  }
  
  /**
   *	__relay_write - write data into the channel
   *	@chan: relay channel
   *	@data: data to be written
   *	@length: number of bytes to write
   *
   *	Writes data into the current cpu's channel buffer.
   *
   *	Protects the buffer by disabling preemption.  Use
   *	relay_write() if you might be logging from interrupt
   *	context.
   */
  static inline void __relay_write(struct rchan *chan,
  				 const void *data,
  				 size_t length)
  {
  	struct rchan_buf *buf;
  
  	buf = chan->buf[get_cpu()];
  	if (unlikely(buf->offset + length > buf->chan->subbuf_size))
  		length = relay_switch_subbuf(buf, length);
  	memcpy(buf->data + buf->offset, data, length);
  	buf->offset += length;
  	put_cpu();
  }
  
  /**
   *	relay_reserve - reserve slot in channel buffer
   *	@chan: relay channel
   *	@length: number of bytes to reserve
   *
   *	Returns pointer to reserved slot, NULL if full.
   *
   *	Reserves a slot in the current cpu's channel buffer.
   *	Does not protect the buffer at all - caller must provide
   *	appropriate synchronization.
   */
  static inline void *relay_reserve(struct rchan *chan, size_t length)
  {
  	void *reserved;
  	struct rchan_buf *buf = chan->buf[smp_processor_id()];
  
  	if (unlikely(buf->offset + length > buf->chan->subbuf_size)) {
  		length = relay_switch_subbuf(buf, length);
  		if (!length)
  			return NULL;
  	}
  	reserved = buf->data + buf->offset;
  	buf->offset += length;
  
  	return reserved;
  }
  
  /**
   *	subbuf_start_reserve - reserve bytes at the start of a sub-buffer
   *	@buf: relay channel buffer
   *	@length: number of bytes to reserve
   *
   *	Helper function used to reserve bytes at the beginning of
   *	a sub-buffer in the subbuf_start() callback.
   */
  static inline void subbuf_start_reserve(struct rchan_buf *buf,
  					size_t length)
  {
  	BUG_ON(length >= buf->chan->subbuf_size - 1);
  	buf->offset = length;
  }
  
  /*
   * exported relay file operations, kernel/relay.c
   */
  extern const struct file_operations relay_file_operations;
  
  #endif /* _LINUX_RELAY_H */
  
  