new helper: copy_page_from_iter()

parallel to copy_page_to_iter().  pipe_write() switched to it (and became
->write_iter()).
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/pipe.c

@@ -116,50 +116,6 @@ void pipe_wait(struct pipe_inode_info *pipe)
 	pipe_lock(pipe);
 }
 
-static int
-pipe_iov_copy_from_user(void *to, struct iovec *iov, unsigned long len,
-			int atomic)
-{
-	unsigned long copy;
-
-	while (len > 0) {
-		while (!iov->iov_len)
-			iov++;
-		copy = min_t(unsigned long, len, iov->iov_len);
-
-		if (atomic) {
-			if (__copy_from_user_inatomic(to, iov->iov_base, copy))
-				return -EFAULT;
-		} else {
-			if (copy_from_user(to, iov->iov_base, copy))
-				return -EFAULT;
-		}
-		to += copy;
-		len -= copy;
-		iov->iov_base += copy;
-		iov->iov_len -= copy;
-	}
-	return 0;
-}
-
-/*
- * Pre-fault in the user memory, so we can use atomic copies.
- */
-static void iov_fault_in_pages_read(struct iovec *iov, unsigned long len)
-{
-	while (!iov->iov_len)
-		iov++;
-
-	while (len > 0) {
-		unsigned long this_len;
-
-		this_len = min_t(unsigned long, len, iov->iov_len);
-		fault_in_pages_readable(iov->iov_base, this_len);
-		len -= this_len;
-		iov++;
-	}
-}
-
 static void anon_pipe_buf_release(struct pipe_inode_info *pipe,
 				  struct pipe_buffer *buf)
 {
@@ -380,24 +336,19 @@ static inline int is_packetized(struct file *file)
 }
 
 static ssize_t
-pipe_write(struct kiocb *iocb, const struct iovec *_iov,
-	    unsigned long nr_segs, loff_t ppos)
+pipe_write(struct kiocb *iocb, struct iov_iter *from)
 {
 	struct file *filp = iocb->ki_filp;
 	struct pipe_inode_info *pipe = filp->private_data;
-	ssize_t ret;
-	int do_wakeup;
-	struct iovec *iov = (struct iovec *)_iov;
-	size_t total_len;
+	ssize_t ret = 0;
+	int do_wakeup = 0;
+	size_t total_len = iov_iter_count(from);
 	ssize_t chars;
 
-	total_len = iov_length(iov, nr_segs);
 	/* Null write succeeds. */
 	if (unlikely(total_len == 0))
 		return 0;
 
-	do_wakeup = 0;
-	ret = 0;
 	__pipe_lock(pipe);
 
 	if (!pipe->readers) {
@@ -416,38 +367,19 @@ pipe_write(struct kiocb *iocb, const struct iovec *_iov,
 		int offset = buf->offset + buf->len;
 
 		if (ops->can_merge && offset + chars <= PAGE_SIZE) {
-			int error, atomic = 1;
-			void *addr;
-
-			error = ops->confirm(pipe, buf);
+			int error = ops->confirm(pipe, buf);
 			if (error)
 				goto out;
 
-			iov_fault_in_pages_read(iov, chars);
-redo1:
-			if (atomic)
-				addr = kmap_atomic(buf->page);
-			else
-				addr = kmap(buf->page);
-			error = pipe_iov_copy_from_user(offset + addr, iov,
-							chars, atomic);
-			if (atomic)
-				kunmap_atomic(addr);
-			else
-				kunmap(buf->page);
-			ret = error;
-			do_wakeup = 1;
-			if (error) {
-				if (atomic) {
-					atomic = 0;
-					goto redo1;
-				}
+			ret = copy_page_from_iter(buf->page, offset, chars, from);
+			if (unlikely(ret < chars)) {
+				error = -EFAULT;
 				goto out;
 			}
+			do_wakeup = 1;
 			buf->len += chars;
-			total_len -= chars;
 			ret = chars;
-			if (!total_len)
+			if (!iov_iter_count(from))
 				goto out;
 		}
 	}
@@ -466,8 +398,7 @@ pipe_write(struct kiocb *iocb, const struct iovec *_iov,
 			int newbuf = (pipe->curbuf + bufs) & (pipe->buffers-1);
 			struct pipe_buffer *buf = pipe->bufs + newbuf;
 			struct page *page = pipe->tmp_page;
-			char *src;
-			int error, atomic = 1;
+			int copied;
 
 			if (!page) {
 				page = alloc_page(GFP_HIGHUSER);
@@ -483,40 +414,19 @@ pipe_write(struct kiocb *iocb, const struct iovec *_iov,
 			 * FIXME! Is this really true?
 			 */
 			do_wakeup = 1;
-			chars = PAGE_SIZE;
-			if (chars > total_len)
-				chars = total_len;
-
-			iov_fault_in_pages_read(iov, chars);
-redo2:
-			if (atomic)
-				src = kmap_atomic(page);
-			else
-				src = kmap(page);
-
-			error = pipe_iov_copy_from_user(src, iov, chars,
-							atomic);
-			if (atomic)
-				kunmap_atomic(src);
-			else
-				kunmap(page);
-
-			if (unlikely(error)) {
-				if (atomic) {
-					atomic = 0;
-					goto redo2;
-				}
+			copied = copy_page_from_iter(page, 0, PAGE_SIZE, from);
+			if (unlikely(copied < PAGE_SIZE && iov_iter_count(from))) {
 				if (!ret)
-					ret = error;
+					ret = -EFAULT;
 				break;
 			}
-			ret += chars;
+			ret += copied;
 
 			/* Insert it into the buffer array */
 			buf->page = page;
 			buf->ops = &anon_pipe_buf_ops;
 			buf->offset = 0;
-			buf->len = chars;
+			buf->len = copied;
 			buf->flags = 0;
 			if (is_packetized(filp)) {
 				buf->ops = &packet_pipe_buf_ops;
@@ -525,8 +435,7 @@ pipe_write(struct kiocb *iocb, const struct iovec *_iov,
 			pipe->nrbufs = ++bufs;
 			pipe->tmp_page = NULL;
 
-			total_len -= chars;
-			if (!total_len)
+			if (!iov_iter_count(from))
 				break;
 		}
 		if (bufs < pipe->buffers)
@@ -1040,8 +949,8 @@ const struct file_operations pipefifo_fops = {
 	.llseek		= no_llseek,
 	.read		= new_sync_read,
 	.read_iter	= pipe_read,
-	.write		= do_sync_write,
-	.aio_write	= pipe_write,
+	.write		= new_sync_write,
+	.write_iter	= pipe_write,
 	.poll		= pipe_poll,
 	.unlocked_ioctl	= pipe_ioctl,
 	.release	= pipe_release,

include/linux/uio.h

@@ -68,6 +68,8 @@ 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);
+size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
+			 struct iov_iter *i);
 unsigned long iov_iter_alignment(const struct iov_iter *i);
 void iov_iter_init(struct iov_iter *i, int direction, const struct iovec *iov,
 			unsigned long nr_segs, size_t count);

mm/iov_iter.c

@@ -82,6 +82,84 @@ size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
 }
 EXPORT_SYMBOL(copy_page_to_iter);
 
+size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
+			 struct iov_iter *i)
+{
+	size_t skip, copy, left, wanted;
+	const struct iovec *iov;
+	char __user *buf;
+	void *kaddr, *to;
+
+	if (unlikely(bytes > i->count))
+		bytes = i->count;
+
+	if (unlikely(!bytes))
+		return 0;
+
+	wanted = bytes;
+	iov = i->iov;
+	skip = i->iov_offset;
+	buf = iov->iov_base + skip;
+	copy = min(bytes, iov->iov_len - skip);
+
+	if (!fault_in_pages_readable(buf, copy)) {
+		kaddr = kmap_atomic(page);
+		to = kaddr + offset;
+
+		/* first chunk, usually the only one */
+		left = __copy_from_user_inatomic(to, buf, copy);
+		copy -= left;
+		skip += copy;
+		to += copy;
+		bytes -= copy;
+
+		while (unlikely(!left && bytes)) {
+			iov++;
+			buf = iov->iov_base;
+			copy = min(bytes, iov->iov_len);
+			left = __copy_from_user_inatomic(to, buf, copy);
+			copy -= left;
+			skip = copy;
+			to += copy;
+			bytes -= copy;
+		}
+		if (likely(!bytes)) {
+			kunmap_atomic(kaddr);
+			goto done;
+		}
+		offset = to - kaddr;
+		buf += copy;
+		kunmap_atomic(kaddr);
+		copy = min(bytes, iov->iov_len - skip);
+	}
+	/* Too bad - revert to non-atomic kmap */
+	kaddr = kmap(page);
+	to = kaddr + offset;
+	left = __copy_from_user(to, buf, copy);
+	copy -= left;
+	skip += copy;
+	to += copy;
+	bytes -= copy;
+	while (unlikely(!left && bytes)) {
+		iov++;
+		buf = iov->iov_base;
+		copy = min(bytes, iov->iov_len);
+		left = __copy_from_user(to, buf, copy);
+		copy -= left;
+		skip = copy;
+		to += copy;
+		bytes -= copy;
+	}
+	kunmap(page);
+done:
+	i->count -= wanted - bytes;
+	i->nr_segs -= iov - i->iov;
+	i->iov = iov;
+	i->iov_offset = skip;
+	return wanted - bytes;
+}
+EXPORT_SYMBOL(copy_page_from_iter);
+
 static size_t __iovec_copy_from_user_inatomic(char *vaddr,
 			const struct iovec *iov, size_t base, size_t bytes)
 {