xfs: hide log iovec alignment constraints

Callers currently have to round out the size of buffers to match the
aligment constraints of log iovecs and xlog_write(). They should not
need to know this detail, so introduce a new function to calculate
the iovec length (for use in ->iop_size implementations). Also
modify xlog_finish_iovec() to round up the length to the correct
alignment so the callers don't need to do this, either.

Convert the only user - inode forks - of this alignment rounding to
use the new interface.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Dave Chinner <david@fromorbit.com>

1 files changed, 39 insertions, 3 deletions

diff --git a/fs/xfs/xfs_log.h b/fs/xfs/xfs_log.h
index 8dafe8f771c7..3a4f6a4e4eb7 100644
--- a/fs/xfs/xfs_log.h
+++ b/fs/xfs/xfs_log.h
@@ -21,23 +21,59 @@ struct xfs_log_vec {
 
 #define XFS_LOG_VEC_ORDERED	(-1)
 
+/*
+ * Calculate the log iovec length for a given user buffer length. Intended to be
+ * used by ->iop_size implementations when sizing buffers of arbitrary
+ * alignments.
+ */
+static inline int
+xlog_calc_iovec_len(int len)
+{
+	return roundup(len, sizeof(uint32_t));
+}
+
 void *xlog_prepare_iovec(struct xfs_log_vec *lv, struct xfs_log_iovec **vecp,
 		uint type);
 
 static inline void
-xlog_finish_iovec(struct xfs_log_vec *lv, struct xfs_log_iovec *vec, int len)
+xlog_finish_iovec(struct xfs_log_vec *lv, struct xfs_log_iovec *vec,
+		int data_len)
 {
 	struct xlog_op_header	*oph = vec->i_addr;
-
-	/* opheader tracks payload length, logvec tracks region length */
+	int			len;
+
+	/*
+	 * Always round up the length to the correct alignment so callers don't
+	 * need to know anything about this log vec layout requirement. This
+	 * means we have to zero the area the data to be written does not cover.
+	 * This is complicated by fact the payload region is offset into the
+	 * logvec region by the opheader that tracks the payload.
+	 */
+	len = xlog_calc_iovec_len(data_len);
+	if (len - data_len != 0) {
+		char	*buf = vec->i_addr + sizeof(struct xlog_op_header);
+
+		memset(buf + data_len, 0, len - data_len);
+	}
+
+	/*
+	 * The opheader tracks aligned payload length, whilst the logvec tracks
+	 * the overall region length.
+	 */
 	oph->oh_len = cpu_to_be32(len);
 
 	len += sizeof(struct xlog_op_header);
 	lv->lv_buf_len += len;
 	lv->lv_bytes += len;
 	vec->i_len = len;
+
+	/* Catch buffer overruns */
+	ASSERT((void *)lv->lv_buf + lv->lv_bytes <= (void *)lv + lv->lv_size);
 }
 
+/*
+ * Copy the amount of data requested by the caller into a new log iovec.
+ */
 static inline void *
 xlog_copy_iovec(struct xfs_log_vec *lv, struct xfs_log_iovec **vecp,
 		uint type, void *data, int len)