fs: fork splice_file_range() from do_splice_direct()

In preparation of calling do_splice_direct() without file_start_write()
held, create a new helper splice_file_range(), to be called from context
of ->copy_file_range() methods instead of do_splice_direct().

Currently, the only difference is that splice_file_range() does not take
flags argument and that it asserts that file_start_write() is held, but
we factor out a common helper do_splice_direct_actor() that will be used
later.

Use the new helper from __ceph_copy_file_range(), that was incorrectly
passing to do_splice_direct() the copy flags argument as splice flags.
The value of copy flags in ceph is always 0, so it is a smenatic bug fix.

Move the declaration of both helpers to linux/splice.h.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Link: https://lore.kernel.org/r/20231130141624.3338942-2-amir73il@gmail.com
Acked-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/ceph/file.c

@@ -12,6 +12,7 @@
 #include <linux/falloc.h>
 #include <linux/iversion.h>
 #include <linux/ktime.h>
+#include <linux/splice.h>
 
 #include "super.h"
 #include "mds_client.h"
@@ -3010,8 +3011,8 @@ static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
 		 * {read,write}_iter, which will get caps again.
 		 */
 		put_rd_wr_caps(src_ci, src_got, dst_ci, dst_got);
-		ret = do_splice_direct(src_file, &src_off, dst_file,
-				       &dst_off, src_objlen, flags);
+		ret = splice_file_range(src_file, &src_off, dst_file, &dst_off,
+					src_objlen);
 		/* Abort on short copies or on error */
 		if (ret < (long)src_objlen) {
 			doutc(cl, "Failed partial copy (%zd)\n", ret);
@@ -3065,8 +3066,8 @@ out_caps:
 	 */
 	if (len && (len < src_ci->i_layout.object_size)) {
 		doutc(cl, "Final partial copy of %zu bytes\n", len);
-		bytes = do_splice_direct(src_file, &src_off, dst_file,
-					 &dst_off, len, flags);
+		bytes = splice_file_range(src_file, &src_off, dst_file,
+					  &dst_off, len);
 		if (bytes > 0)
 			ret += bytes;
 		else

fs/read_write.c

@@ -1423,10 +1423,8 @@ ssize_t generic_copy_file_range(struct file *file_in, loff_t pos_in,
 				struct file *file_out, loff_t pos_out,
 				size_t len, unsigned int flags)
 {
-	lockdep_assert(file_write_started(file_out));
-
-	return do_splice_direct(file_in, &pos_in, file_out, &pos_out,
-				len > MAX_RW_COUNT ? MAX_RW_COUNT : len, 0);
+	return splice_file_range(file_in, &pos_in, file_out, &pos_out,
+				 min_t(size_t, len, MAX_RW_COUNT));
 }
 EXPORT_SYMBOL(generic_copy_file_range);
 

fs/splice.c

@@ -1170,6 +1170,34 @@ static void direct_file_splice_eof(struct splice_desc *sd)
 		file->f_op->splice_eof(file);
 }
 
+static long do_splice_direct_actor(struct file *in, loff_t *ppos,
+				   struct file *out, loff_t *opos,
+				   size_t len, unsigned int flags,
+				   splice_direct_actor *actor)
+{
+	struct splice_desc sd = {
+		.len		= len,
+		.total_len	= len,
+		.flags		= flags,
+		.pos		= *ppos,
+		.u.file		= out,
+		.splice_eof	= direct_file_splice_eof,
+		.opos		= opos,
+	};
+	long ret;
+
+	if (unlikely(!(out->f_mode & FMODE_WRITE)))
+		return -EBADF;
+
+	if (unlikely(out->f_flags & O_APPEND))
+		return -EINVAL;
+
+	ret = splice_direct_to_actor(in, &sd, actor);
+	if (ret > 0)
+		*ppos = sd.pos;
+
+	return ret;
+}
 /**
  * do_splice_direct - splices data directly between two files
  * @in:		file to splice from
@@ -1190,31 +1218,34 @@ static void direct_file_splice_eof(struct splice_desc *sd)
 long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
 		      loff_t *opos, size_t len, unsigned int flags)
 {
-	struct splice_desc sd = {
-		.len		= len,
-		.total_len	= len,
-		.flags		= flags,
-		.pos		= *ppos,
-		.u.file		= out,
-		.splice_eof	= direct_file_splice_eof,
-		.opos		= opos,
-	};
-	long ret;
-
-	if (unlikely(!(out->f_mode & FMODE_WRITE)))
-		return -EBADF;
-
-	if (unlikely(out->f_flags & O_APPEND))
-		return -EINVAL;
-
-	ret = splice_direct_to_actor(in, &sd, direct_splice_actor);
-	if (ret > 0)
-		*ppos = sd.pos;
-
-	return ret;
+	return do_splice_direct_actor(in, ppos, out, opos, len, flags,
+				      direct_splice_actor);
 }
 EXPORT_SYMBOL(do_splice_direct);
 
+/**
+ * splice_file_range - splices data between two files for copy_file_range()
+ * @in:		file to splice from
+ * @ppos:	input file offset
+ * @out:	file to splice to
+ * @opos:	output file offset
+ * @len:	number of bytes to splice
+ *
+ * Description:
+ *    For use by generic_copy_file_range() and ->copy_file_range() methods.
+ *
+ * Callers already called rw_verify_area() on the entire range.
+ */
+long splice_file_range(struct file *in, loff_t *ppos, struct file *out,
+		       loff_t *opos, size_t len)
+{
+	lockdep_assert(file_write_started(out));
+
+	return do_splice_direct_actor(in, ppos, out, opos, len, 0,
+				      direct_splice_actor);
+}
+EXPORT_SYMBOL(splice_file_range);
+
 static int wait_for_space(struct pipe_inode_info *pipe, unsigned flags)
 {
 	for (;;) {

include/linux/fs.h

@@ -3052,8 +3052,6 @@ ssize_t copy_splice_read(struct file *in, loff_t *ppos,
 			 size_t len, unsigned int flags);
 extern ssize_t iter_file_splice_write(struct pipe_inode_info *,
 		struct file *, loff_t *, size_t, unsigned int);
-extern long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
-		loff_t *opos, size_t len, unsigned int flags);
 
 
 extern void

include/linux/splice.h

@@ -80,11 +80,14 @@ extern ssize_t add_to_pipe(struct pipe_inode_info *,
 long vfs_splice_read(struct file *in, loff_t *ppos,
 		     struct pipe_inode_info *pipe, size_t len,
 		     unsigned int flags);
-extern ssize_t splice_direct_to_actor(struct file *, struct splice_desc *,
-				      splice_direct_actor *);
-extern long do_splice(struct file *in, loff_t *off_in,
-		      struct file *out, loff_t *off_out,
-		      size_t len, unsigned int flags);
+ssize_t splice_direct_to_actor(struct file *file, struct splice_desc *sd,
+			       splice_direct_actor *actor);
+long do_splice(struct file *in, loff_t *off_in, struct file *out,
+	       loff_t *off_out, size_t len, unsigned int flags);
+long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
+		      loff_t *opos, size_t len, unsigned int flags);
+long splice_file_range(struct file *in, loff_t *ppos, struct file *out,
+		       loff_t *opos, size_t len);
 
 extern long do_tee(struct file *in, struct file *out, size_t len,
 		   unsigned int flags);