fuse: pass iov[] to fuse_get_user_pages()

The patch makes preliminary work for the next patch optimizing scatter-gather
direct IO. The idea is to allow fuse_get_user_pages() to pack as many iov-s
to each fuse request as possible. So, here we only rework all related
call-paths to carry iov[] from fuse_direct_IO() to fuse_get_user_pages().
Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

fs/fuse/file.c

@@ -1056,14 +1056,18 @@ static inline void fuse_page_descs_length_init(struct fuse_req *req)
 			req->page_descs[i].offset;
 }
 
-static int fuse_get_user_pages(struct fuse_req *req, const char __user *buf,
+static int fuse_get_user_pages(struct fuse_req *req, struct iov_iter *ii,
 			       size_t *nbytesp, int write)
 {
 	size_t nbytes = *nbytesp;
-	unsigned long user_addr = (unsigned long) buf;
-	unsigned offset = user_addr & ~PAGE_MASK;
+	size_t frag_size = min(iov_iter_single_seg_count(ii), nbytes);
+	unsigned long user_addr;
+	unsigned offset;
 	int npages;
 
+	user_addr = (unsigned long)ii->iov->iov_base + ii->iov_offset;
+	offset = user_addr & ~PAGE_MASK;
+
 	/* Special case for kernel I/O: can copy directly into the buffer */
 	if (segment_eq(get_fs(), KERNEL_DS)) {
 		if (write)
@@ -1071,10 +1075,12 @@ static int fuse_get_user_pages(struct fuse_req *req, const char __user *buf,
 		else
 			req->out.args[0].value = (void *) user_addr;
 
+		iov_iter_advance(ii, frag_size);
+		*nbytesp = frag_size;
 		return 0;
 	}
 
-	nbytes = min_t(size_t, nbytes, FUSE_MAX_PAGES_PER_REQ << PAGE_SHIFT);
+	nbytes = min_t(size_t, frag_size, FUSE_MAX_PAGES_PER_REQ << PAGE_SHIFT);
 	npages = (nbytes + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	npages = clamp(npages, 1, FUSE_MAX_PAGES_PER_REQ);
 	npages = get_user_pages_fast(user_addr, npages, !write, req->pages);
@@ -1092,17 +1098,19 @@ static int fuse_get_user_pages(struct fuse_req *req, const char __user *buf,
 
 	nbytes = (req->num_pages << PAGE_SHIFT) - req->page_descs[0].offset;
 
-	if (*nbytesp < nbytes)
+	if (frag_size < nbytes)
 		req->page_descs[req->num_pages - 1].length -=
-			nbytes - *nbytesp;
+			nbytes - frag_size;
 
-	*nbytesp = min(*nbytesp, nbytes);
+	*nbytesp = min(frag_size, nbytes);
+	iov_iter_advance(ii, *nbytesp);
 
 	return 0;
 }
 
-ssize_t fuse_direct_io(struct file *file, const char __user *buf,
-		       size_t count, loff_t *ppos, int write)
+static ssize_t __fuse_direct_io(struct file *file, const struct iovec *iov,
+				unsigned long nr_segs, size_t count,
+				loff_t *ppos, int write)
 {
 	struct fuse_file *ff = file->private_data;
 	struct fuse_conn *fc = ff->fc;
@@ -1110,6 +1118,9 @@ ssize_t fuse_direct_io(struct file *file, const char __user *buf,
 	loff_t pos = *ppos;
 	ssize_t res = 0;
 	struct fuse_req *req;
+	struct iov_iter ii;
+
+	iov_iter_init(&ii, iov, nr_segs, count, 0);
 
 	req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
 	if (IS_ERR(req))
@@ -1119,7 +1130,7 @@ ssize_t fuse_direct_io(struct file *file, const char __user *buf,
 		size_t nres;
 		fl_owner_t owner = current->files;
 		size_t nbytes = min(count, nmax);
-		int err = fuse_get_user_pages(req, buf, &nbytes, write);
+		int err = fuse_get_user_pages(req, &ii, &nbytes, write);
 		if (err) {
 			res = err;
 			break;
@@ -1142,7 +1153,6 @@ ssize_t fuse_direct_io(struct file *file, const char __user *buf,
 		count -= nres;
 		res += nres;
 		pos += nres;
-		buf += nres;
 		if (nres != nbytes)
 			break;
 		if (count) {
@@ -1159,10 +1169,17 @@ ssize_t fuse_direct_io(struct file *file, const char __user *buf,
 
 	return res;
 }
+
+ssize_t fuse_direct_io(struct file *file, const char __user *buf,
+		       size_t count, loff_t *ppos, int write)
+{
+	struct iovec iov = { .iov_base = (void *)buf, .iov_len = count };
+	return __fuse_direct_io(file, &iov, 1, count, ppos, write);
+}
 EXPORT_SYMBOL_GPL(fuse_direct_io);
 
-static ssize_t fuse_direct_read(struct file *file, char __user *buf,
-				     size_t count, loff_t *ppos)
+static ssize_t __fuse_direct_read(struct file *file, const struct iovec *iov,
+				  unsigned long nr_segs, loff_t *ppos)
 {
 	ssize_t res;
 	struct inode *inode = file->f_path.dentry->d_inode;
@@ -1170,22 +1187,31 @@ static ssize_t fuse_direct_read(struct file *file, char __user *buf,
 	if (is_bad_inode(inode))
 		return -EIO;
 
-	res = fuse_direct_io(file, buf, count, ppos, 0);
+	res = __fuse_direct_io(file, iov, nr_segs, iov_length(iov, nr_segs),
+			       ppos, 0);
 
 	fuse_invalidate_attr(inode);
 
 	return res;
 }
 
-static ssize_t __fuse_direct_write(struct file *file, const char __user *buf,
+static ssize_t fuse_direct_read(struct file *file, char __user *buf,
 				     size_t count, loff_t *ppos)
+{
+	struct iovec iov = { .iov_base = (void *)buf, .iov_len = count };
+	return __fuse_direct_read(file, &iov, 1, ppos);
+}
+
+static ssize_t __fuse_direct_write(struct file *file, const struct iovec *iov,
+				   unsigned long nr_segs, loff_t *ppos)
 {
 	struct inode *inode = file->f_path.dentry->d_inode;
+	size_t count = iov_length(iov, nr_segs);
 	ssize_t res;
 
 	res = generic_write_checks(file, ppos, &count, 0);
 	if (!res) {
-		res = fuse_direct_io(file, buf, count, ppos, 1);
+		res = __fuse_direct_io(file, iov, nr_segs, count, ppos, 1);
 		if (res > 0)
 			fuse_write_update_size(inode, *ppos);
 	}
@@ -1198,6 +1224,7 @@ static ssize_t __fuse_direct_write(struct file *file, const char __user *buf,
 static ssize_t fuse_direct_write(struct file *file, const char __user *buf,
 				 size_t count, loff_t *ppos)
 {
+	struct iovec iov = { .iov_base = (void *)buf, .iov_len = count };
 	struct inode *inode = file->f_path.dentry->d_inode;
 	ssize_t res;
 
@@ -1206,7 +1233,7 @@ static ssize_t fuse_direct_write(struct file *file, const char __user *buf,
 
 	/* Don't allow parallel writes to the same file */
 	mutex_lock(&inode->i_mutex);
-	res = __fuse_direct_write(file, buf, count, ppos);
+	res = __fuse_direct_write(file, &iov, 1, ppos);
 	mutex_unlock(&inode->i_mutex);
 
 	return res;
@@ -2167,41 +2194,6 @@ int fuse_notify_poll_wakeup(struct fuse_conn *fc,
 	return 0;
 }
 
-static ssize_t fuse_loop_dio(struct file *filp, const struct iovec *iov,
-			     unsigned long nr_segs, loff_t *ppos, int rw)
-{
-	const struct iovec *vector = iov;
-	ssize_t ret = 0;
-
-	while (nr_segs > 0) {
-		void __user *base;
-		size_t len;
-		ssize_t nr;
-
-		base = vector->iov_base;
-		len = vector->iov_len;
-		vector++;
-		nr_segs--;
-
-		if (rw == WRITE)
-			nr = __fuse_direct_write(filp, base, len, ppos);
-		else
-			nr = fuse_direct_read(filp, base, len, ppos);
-
-		if (nr < 0) {
-			if (!ret)
-				ret = nr;
-			break;
-		}
-		ret += nr;
-		if (nr != len)
-			break;
-	}
-
-	return ret;
-}
-
-
 static ssize_t
 fuse_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
 			loff_t offset, unsigned long nr_segs)
@@ -2213,7 +2205,10 @@ fuse_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
 	file = iocb->ki_filp;
 	pos = offset;
 
-	ret = fuse_loop_dio(file, iov, nr_segs, &pos, rw);
+	if (rw == WRITE)
+		ret = __fuse_direct_write(file, iov, nr_segs, &pos);
+	else
+		ret = __fuse_direct_read(file, iov, nr_segs, &pos);
 
 	return ret;
 }