NAME    [Toc]    [Back]

       buf - General: Describes arbitrary I/O

SYNOPSIS    [Toc]    [Back]

       ----------------------------------
       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    [Toc]    [Back]

       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    [Toc]    [Back]

       The buf data structure describes  arbitrary  I/O,  but  is
       usually  associated  with  block  I/O  and physio.  A systemwide
 pool of buf data structures 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 completed.
   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    [Toc]    [Back]

       The   operating system does not define a B_CALL flag.  The
       iodone routine checks the b_iodone member to determine  if
       you  specified  a completion 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    [Toc]    [Back]

                                                          buf(9s)