ll_rw_block(9) [suse man page]

LL_RW_BLOCK(9)							   The Linux VFS						    LL_RW_BLOCK(9)

NAME

       ll_rw_block - level access to block devices (DEPRECATED)

SYNOPSIS

       void ll_rw_block(int rw, int nr, struct buffer_head * bhs[]);

ARGUMENTS

       rw
	   whether to READ or WRITE or SWRITE or maybe READA (readahead)

       nr
	   number of struct buffer_heads in the array

       bhs[]
	   array of pointers to struct buffer_head

DESCRIPTION

       ll_rw_block takes an array of pointers to struct buffer_heads, and requests an I/O operation on them, either a READ or a WRITE. The third
       SWRITE is like WRITE only we make sure that the *current* data in buffers are sent to disk. The fourth READA option is described in the
       documentation for generic_make_request which ll_rw_block calls.

       This function drops any buffer that it cannot get a lock on (with the BH_Lock state bit) unless SWRITE is required, any buffer that appears
       to be clean when doing a write request, and any buffer that appears to be up-to-date when doing read request. Further it marks as clean
       buffers that are processed for writing (the buffer cache won't assume that they are actually clean until the buffer gets unlocked).

       ll_rw_block sets b_end_io to simple completion handler that marks the buffer up-to-date (if approriate), unlocks the buffer and wakes any
       waiters.

       All of the buffers must be for the same device, and must also be a multiple of the current approved size for the device.

COPYRIGHT

Kernel Hackers Manual 2.6.					     July 2010							    LL_RW_BLOCK(9)

JOURNAL_GET_UNDO_ACC(9) 				     The Linux Journalling API					   JOURNAL_GET_UNDO_ACC(9)

NAME

       journal_get_undo_access - Notify intent to modify metadata with non-rewindable consequences

SYNOPSIS

       int journal_get_undo_access(handle_t * handle, struct buffer_head * bh);

ARGUMENTS

       handle
	   transaction

       bh
	   buffer to undo

DESCRIPTION

       Sometimes there is a need to distinguish between metadata which has been committed to disk and that which has not. The ext3fs code uses
       this for freeing and allocating space, we have to make sure that we do not reuse freed space until the deallocation has been committed,
       since if we overwrote that space we would make the delete un-rewindable in case of a crash.

       To deal with that, journal_get_undo_access requests write access to a buffer for parts of non-rewindable operations such as delete
       operations on the bitmaps. The journaling code must keep a copy of the buffer's contents prior to the undo_access call until such time as
       we know that the buffer has definitely been committed to disk.

       We never need to know which transaction the committed data is part of, buffers touched here are guaranteed to be dirtied later and so will
       be committed to a new transaction in due course, at which point we can discard the old committed data pointer.

       Returns error number or 0 on success.

AUTHORS

       Roger Gammans <rgammans@computer-surgery.co.uk>
	   Author.

       Stephen Tweedie <sct@redhat.com>
	   Author.

COPYRIGHT

Kernel Hackers Manual 3.10					     June 2014						   JOURNAL_GET_UNDO_ACC(9)