new primitive: iov_iter_alignment()

returns the value aligned as badly as the worst remaining segment
in iov_iter is.  Use instead of open-coded equivalents.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

drivers/staging/lustre/lustre/llite/rw26.c

@@ -391,11 +391,8 @@ static ssize_t ll_direct_IO_26(int rw, struct kiocb *iocb,
 	       MAX_DIO_SIZE >> PAGE_CACHE_SHIFT);
 
 	/* Check that all user buffers are aligned as well */
-	for (seg = 0; seg < iter->nr_segs; seg++) {
-		if (((unsigned long)iter->iov[seg].iov_base & ~CFS_PAGE_MASK) ||
-		    (iter->iov[seg].iov_len & ~CFS_PAGE_MASK))
-			return -EINVAL;
-	}
+	if (iov_iter_alignment(iter) & ~CFS_PAGE_MASK)
+		return -EINVAL;
 
 	env = cl_env_get(&refcheck);
 	LASSERT(!IS_ERR(env));

fs/direct-io.c

@@ -1112,19 +1112,18 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
 	dio_submit_t submit_io,	int flags)
 {
 	int seg;
-	size_t size;
-	unsigned long addr;
 	unsigned i_blkbits = ACCESS_ONCE(inode->i_blkbits);
 	unsigned blkbits = i_blkbits;
 	unsigned blocksize_mask = (1 << blkbits) - 1;
 	ssize_t retval = -EINVAL;
-	loff_t end = offset;
+	loff_t end = offset + iov_iter_count(iter);
 	struct dio *dio;
 	struct dio_submit sdio = { 0, };
 	unsigned long user_addr;
 	size_t bytes;
 	struct buffer_head map_bh = { 0, };
 	struct blk_plug plug;
+	unsigned long align = offset | iov_iter_alignment(iter);
 
 	if (rw & WRITE)
 		rw = WRITE_ODIRECT;
@@ -1134,32 +1133,16 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
 	 * the early prefetch in the caller enough time.
 	 */
 
-	if (offset & blocksize_mask) {
+	if (align & blocksize_mask) {
 		if (bdev)
 			blkbits = blksize_bits(bdev_logical_block_size(bdev));
 		blocksize_mask = (1 << blkbits) - 1;
-		if (offset & blocksize_mask)
+		if (align & blocksize_mask)
 			goto out;
 	}
 
-	/* Check the memory alignment.  Blocks cannot straddle pages */
-	for (seg = 0; seg < iter->nr_segs; seg++) {
-		addr = (unsigned long)iter->iov[seg].iov_base;
-		size = iter->iov[seg].iov_len;
-		end += size;
-		if (unlikely((addr & blocksize_mask) ||
-			     (size & blocksize_mask))) {
-			if (bdev)
-				blkbits = blksize_bits(
-					 bdev_logical_block_size(bdev));
-			blocksize_mask = (1 << blkbits) - 1;
-			if ((addr & blocksize_mask) || (size & blocksize_mask))
-				goto out;
-		}
-	}
-
 	/* watch out for a 0 len io from a tricksy fs */
-	if (rw == READ && end == offset)
+	if (rw == READ && !iov_iter_count(iter))
 		return 0;
 
 	dio = kmem_cache_alloc(dio_cache, GFP_KERNEL);

include/linux/uio.h

@@ -67,6 +67,7 @@ int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes);
 size_t iov_iter_single_seg_count(const struct iov_iter *i);
 size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
 			 struct iov_iter *i);
+unsigned long iov_iter_alignment(const struct iov_iter *i);
 
 static inline void iov_iter_init(struct iov_iter *i,
 			const struct iovec *iov, unsigned long nr_segs,
@@ -88,4 +89,5 @@ static inline size_t iov_iter_count(struct iov_iter *i)
 int memcpy_fromiovec(unsigned char *kdata, struct iovec *iov, int len);
 int memcpy_toiovec(struct iovec *iov, unsigned char *kdata, int len);
 
+
 #endif

mm/iov_iter.c

@@ -195,3 +195,28 @@ size_t iov_iter_single_seg_count(const struct iov_iter *i)
 		return min(i->count, iov->iov_len - i->iov_offset);
 }
 EXPORT_SYMBOL(iov_iter_single_seg_count);
+
+unsigned long iov_iter_alignment(const struct iov_iter *i)
+{
+	const struct iovec *iov = i->iov;
+	unsigned long res;
+	size_t size = i->count;
+	size_t n;
+
+	if (!size)
+		return 0;
+
+	res = (unsigned long)iov->iov_base + i->iov_offset;
+	n = iov->iov_len - i->iov_offset;
+	if (n >= size)
+		return res | size;
+	size -= n;
+	res |= n;
+	while (size > (++iov)->iov_len) {
+		res |= (unsigned long)iov->iov_base | iov->iov_len;
+		size -= iov->iov_len;
+	}
+	res |= (unsigned long)iov->iov_base | size;
+	return res;
+}
+EXPORT_SYMBOL(iov_iter_alignment);