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cvs commit: src/sys/kern vfs_journal.c src/sys/sys kern_syscall.h mountctl.h

From: Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxxxxx>
Date: Thu, 30 Dec 2004 13:41:06 -0800 (PST)

dillon      2004/12/30 13:41:06 PST

DragonFly src repository

  Modified files:
    sys/kern             vfs_journal.c 
    sys/sys              kern_syscall.h mountctl.h 
  Journaling layer work.  Lock down the journaling data format and most
  of the record-building API.
  The Journaling data format consists of two layers, A logical stream
  abstraction layer and a recursive subrecord layer.
  The memory FIFO and worker thread only deals with the logical stream
  abstraction layer.  subrecord data is broken down into logical stream
  records which the worker thread then writes out to the journal.  Space
  for a logical stream record is 'reserved' and then filled in by the
  journaling operation.  Other threads can reserve their own space in the
  memory FIFO, even if earlier reservations have not yet been committed.
  The worker thread will only write out completed records and it currently
  does so in sequential order, so the worker thread itself may stall
  temporarily if the next reservation in the FIFO has not yet been completed.
  (this will probably have to be changed in the future but for now its the
  easiest solution, allowing for some parallelism without creating too big
  a mess).
  Each logical stream is a (typically) short-lived entity, usually
  encompassing a single VFS operation, but may be made up of multiple
  stream records.  The stream records contain a stream id and bits specifying
  whether the record is beginning a new logical stream, in the middle
  somewhere, or ending a logical stream.  Small transactions may be able
  to fit in a single record in which case multiple bits may be set.
  Very large transactions, for example when someone does a write(... 10MB),
  are fully supported and would likely generate a large number of stream
  records.  Such transactions would not necessarily stall other operations
  from other processes, however, since they would be broken up into smaller
  pieces for output to the journal.
  The stream layer serves to multiplex individual logical streams onto
  the memory FIFO and out the journaling stream descriptor.
  The recursive subrecord layer identifies the transaction as well as any
  other necessary data, including UNDO data if the journal is reversable.
  A single transaction may contain several sub-records identifying the bits
  making up the transaction (for example, a 'mkdir' transaction would need
  a subrecord identifying the userid, groupid, file modes, and path).
  The record formats also allow for transactional aborts, even if some of the
  data has already been pushed out to the descriptor due to limited buffer
  space.  And, finally, while the subrecord's header format includes a record
  size field, this value may not be known for subrecords representing
  recusive 'pushes' since the header may be flushed out to the journal long
  before the record is completed.  This case is also fully supported.
  NOTE: The memory FIFO used to ship data to the worker thread is serialized
  by the BGL for the moment, but will eventually be made per-cpu to support
  lockless operation under SMP.
  Revision  Changes    Path
  1.4       +834 -57   src/sys/kern/vfs_journal.c
  1.25      +1 -0      src/sys/sys/kern_syscall.h
  1.3       +245 -15   src/sys/sys/mountctl.h


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