[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: 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>
diff --git a/fs/buffer.c b/fs/buffer.c
index 7ff6e93..a4b8242 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1440,6 +1440,7 @@
clear_buffer_req(bh);
clear_buffer_new(bh);
clear_buffer_delay(bh);
+ clear_buffer_unwritten(bh);
unlock_buffer(bh);
}
@@ -1823,6 +1824,7 @@
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 @@
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);
diff --git a/fs/xfs/linux-2.6/xfs_linux.h b/fs/xfs/linux-2.6/xfs_linux.h
index 2b0e001..715adad 100644
--- a/fs/xfs/linux-2.6/xfs_linux.h
+++ b/fs/xfs/linux-2.6/xfs_linux.h
@@ -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
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 5d9fb0e..ffbdb66 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -34,6 +34,7 @@
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(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)