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[PATCH] Make BH_Unwritten a first class bufferhead flag V2

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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: Dave Chinner <dgc@sgi.com>
Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
David Chinner 2007-02-12 00:51:41 -08:00 committed by Linus Torvalds
parent 42da9cbd3e
commit 33a266dda9
3 changed files with 5 additions and 11 deletions
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4
fs/buffer.c
View file

@ -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);

10
fs/xfs/linux-2.6/xfs_linux.h
View file

@ -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

2
include/linux/buffer_head.h
View file

@ -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)