xfs: use larger in-core attr firstused field and detect overflow
The on-disk xfs_attr3_leaf_hdr structure firstused field is 16-bit and
subject to overflow when fs block size is 64k. The field is typically
initialized to block size when an attr leaf block is initialized. This
problem is demonstrated by assert failures when running xfstests
generic/117 on an fs with 64k blocks.
To support the existing attr leaf block algorithms for insertion,
rebalance and entry movement, increase the size of the in-core firstused
field to 32-bit and handle the potential overflow on conversion to/from
the on-disk structure. If the overflow condition occurs, set a special
value in the firstused field that is translated back on header read. The
special value is only required in the case of an empty 64k attr block. A
value of zero is used because firstused is initialized to the block size
and grows backwards from there. Furthermore, the attribute block header
occupies the first bytes of the block. Thus, a value of zero has no
other legitimate meaning for this structure. Two new conversion helpers
are created to manage the conversion of firstused to and from disk.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
diff --git a/fs/xfs/libxfs/xfs_da_format.h b/fs/xfs/libxfs/xfs_da_format.h
index 0a49b02..74bcbab 100644
--- a/fs/xfs/libxfs/xfs_da_format.h
+++ b/fs/xfs/libxfs/xfs_da_format.h
@@ -725,7 +725,13 @@
__uint16_t magic;
__uint16_t count;
__uint16_t usedbytes;
- __uint16_t firstused;
+ /*
+ * firstused is 32-bit here instead of 16-bit like the on-disk variant
+ * to support maximum fsb size of 64k without overflow issues throughout
+ * the attr code. Instead, the overflow condition is handled on
+ * conversion to/from disk.
+ */
+ __uint32_t firstused;
__u8 holes;
struct {
__uint16_t base;
@@ -734,6 +740,12 @@
};
/*
+ * Special value to represent fs block size in the leaf header firstused field.
+ * Only used when block size overflows the 2-bytes available on disk.
+ */
+#define XFS_ATTR3_LEAF_NULLOFF 0
+
+/*
* Flags used in the leaf_entry[i].flags field.
* NOTE: the INCOMPLETE bit must not collide with the flags bits specified
* on the system call, they are "or"ed together for various operations.