[Devel] [PATCH 4/4] fuse: re-work fuse_direct_IO()

[Maxim Patlasov]

The patch eliminates fuse_loop_dio() by passing iovec[] transparently
from fuse_direct_IO() to __fuse_direct_io(). The latter is responsible now
for processing elements of iovec[]. This allows __fuse_direct_io() to pack
many iovec-s to each fuse_req, effectively minimizing number of fuse_req-s
required.

Signed-off-by: Maxim Patlasov <mpatlasov at parallels.com>
---
 fs/fuse/file.c |   64 ++++++++++++++++++--------------------------------------
 1 files changed, 21 insertions(+), 43 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 6c8e24f..0355128 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1158,8 +1158,8 @@ ssize_t fuse_direct_io(struct file *file, const char __user *buf,
 }
 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;
@@ -1167,22 +1167,31 @@ 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,
-				   size_t count, loff_t *ppos)
+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);
 	}
@@ -1195,6 +1204,7 @@ 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;
 
@@ -1203,7 +1213,7 @@ 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;
@@ -2161,41 +2171,6 @@ 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)
@@ -2207,7 +2182,10 @@ 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;
 }