buf(9s) 																   buf(9s)

NAME

       buf - General: Describes arbitrary I/O

SYNOPSIS

       ----------------------------------
       Member Name   Data Type
       ----------------------------------
       b_flags	     int
       b_forw	     struct buf *
       b_back	     struct buf *
       av_forw	     struct buf *
       av_back	     struct buf *
       b_bcount      int
       b_error	     short
       b_dev	     dev_t
       b_un.b_addr   caddr_t
       b_lblkno      daddr_t
       b_blkno	     daddr_t
       b_resid	     int
       b_iodone      void (*b_iodone) ()
       b_proc	     struct proc *
       ----------------------------------

MEMBERS

       Specifies  binary  status  flags.  These flags indicate how a request is to be handled and the current status of the request. The following
       flags are applicable to kernel modules that are device drivers: B_READ, B_DONE, B_ERROR, B_BUSY, and B_PHYS. See  the  DESCRIPTION  section
       for more information on these flags.  Specifies a hash chain. Only the entity (driver, buffer cache) that owns the buf structure can use or
       reference this member. A driver receiving a buf structure from the buffer cache through the strategy routine  must  not	use  this  member.
       Specifies  a  hash  chain.  Only  the  entity (driver, buffer cache) that owns the buf structure can use or reference this member. A driver
       receiving a buf structure from the buffer cache through the strategy routine must not use this member.  Specifies the position on the  free
       list  if  the  b_flags  member  is  not set to B_BUSY.  Specifies the position on the free list if the b_flags member is not set to B_BUSY.
       Specifies the size of the requested transfer (in bytes).  Specifies that an error occurred on this data transfer. This member is set to	an
       error  code  if	the b_flags member bit was set.  Specifies the special device to which the transfer is directed.  Specifies the address at
       which to pull or push the data.	Specifies the logical block number.  Specifies the block number on the partition of a disk or on the  file
       system.	 Specifies  (in bytes) the data not transferred because of some error.	Specifies the routine called by iodone.  The device driver
       calls iodone at the completion of an I/O operation.  Specifies a pointer to the proc structure that represents the process  performing  the
       I/O.

DESCRIPTION

       The  buf data structure describes arbitrary I/O, but is usually associated with block I/O and physio.  A systemwide pool of buf data struc-
       tures exists for block I/O; however, many kernel modules that are device drivers also include locally defined buf data structures.

       Kernel modules can use the following flags with the b_flags member: This flag is set if the operation is read and cleared if the  operation
       is write.  This flag is cleared when a request is passed to a driver strategy routine. The writer must call iodone to mark a buffer as com-
       pleted.	This flag specifies that an error occurred on this data transfer.  Kernel modules set this flag if an  error  occurs.	This  flag
       indicates that the buffer is in use.  This flag indicates that the associated data is in user address space.

NOTES

       The  operating system does not define a B_CALL flag.  The iodone routine checks the b_iodone member to determine if you specified a comple-
       tion routine. If so, iodone clears b_iodone and then calls the specified completion routine. If you want to reuse this buf data	structure,
       you must reset the b_iodone member to a completion routine. In fact, it is good programming practice to reset all of the referenced members
       of a buf data structure that you plan to reuse.

FILES

																	   buf(9s)