Commit 33a266dd authored by David Chinner's avatar David Chinner Committed by Linus Torvalds
Browse files

[PATCH] Make BH_Unwritten a first class bufferhead flag V2 

Currently, XFS uses BH_PrivateStart for flagging unwritten extent state in a
bufferhead.  Recently, I found the long standing mmap/unwritten extent
conversion bug, and it was to do with partial page invalidation not clearing
the unwritten flag from bufferheads attached to the page but beyond EOF.  See
here for a full explaination:

http://oss.sgi.com/archives/xfs/2006-12/msg00196.html

The solution I have checked into the XFS dev tree involves duplicating code
from block_invalidatepage to clear the unwritten flag from the bufferhead(s),
and then calling block_invalidatepage() to do the rest.

Christoph suggested that this would be better solved by pushing the unwritten
flag into the common buffer head flags and just adding the call to
discard_buffer():

http://oss.sgi.com/archives/xfs/2006-12/msg00239.html



The following patch makes BH_Unwritten a first class citizen.

Signed-off-by: default avatarDave Chinner <dgc@sgi.com>
Acked-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 42da9cbd

fs/buffer.c

+3 −1
Original line number Diff line number Diff line
@@ -1440,6 +1440,7 @@ static void discard_buffer(struct buffer_head * bh) 
	clear_buffer_req(bh);

	clear_buffer_new(bh);

	clear_buffer_delay(bh);

	clear_buffer_unwritten(bh);

	unlock_buffer(bh);

}
@@ -1823,6 +1824,7 @@ static int __block_prepare_write(struct inode *inode, struct page *page, 
			continue; 

		}

		if (!buffer_uptodate(bh) && !buffer_delay(bh) &&

		    !buffer_unwritten(bh) &&

		     (block_start < from || block_end > to)) {

			ll_rw_block(READ, 1, &bh);

			*wait_bh++=bh;
@@ -2544,7 +2546,7 @@ int block_truncate_page(struct address_space *mapping, 
	if (PageUptodate(page))

		set_buffer_uptodate(bh);



	if (!buffer_uptodate(bh) && !buffer_delay(bh)) {

	if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {

		err = -EIO;

		ll_rw_block(READ, 1, &bh);

		wait_on_buffer(bh);

fs/xfs/linux-2.6/xfs_linux.h

+0 −10
Original line number Diff line number Diff line
@@ -109,16 +109,6 @@ 
#undef  HAVE_PERCPU_SB	/* per cpu superblock counters are a 2.6 feature */

#endif



/*

 * State flag for unwritten extent buffers.

 *

 * We need to be able to distinguish between these and delayed

 * allocate buffers within XFS.  The generic IO path code does

 * not need to distinguish - we use the BH_Delay flag for both

 * delalloc and these ondisk-uninitialised buffers.

 */

BUFFER_FNS(PrivateStart, unwritten);



#define restricted_chown	xfs_params.restrict_chown.val

#define irix_sgid_inherit	xfs_params.sgid_inherit.val

#define irix_symlink_mode	xfs_params.symlink_mode.val

include/linux/buffer_head.h

+2 −0
Original line number Diff line number Diff line
@@ -34,6 +34,7 @@ enum bh_state_bits { 
	BH_Write_EIO,	/* I/O error on write */

	BH_Ordered,	/* ordered write */

	BH_Eopnotsupp,	/* operation not supported (barrier) */

	BH_Unwritten,	/* Buffer is allocated on disk but not written */



	BH_PrivateStart,/* not a state bit, but the first bit available

			 * for private allocation by other entities
@@ -126,6 +127,7 @@ BUFFER_FNS(Boundary, boundary) 
BUFFER_FNS(Write_EIO, write_io_error)

BUFFER_FNS(Ordered, ordered)

BUFFER_FNS(Eopnotsupp, eopnotsupp)

BUFFER_FNS(Unwritten, unwritten)



#define bh_offset(bh)		((unsigned long)(bh)->b_data & ~PAGE_MASK)

#define touch_buffer(bh)	mark_page_accessed(bh->b_page)

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