[PATCH 4/9] vfs: Add vfs_copy_file_range() support for pagecache copies

["Darrick J. Wong" <darrick.wong@xxxxxxxxxx>]

>From : Anna Schumaker <Anna.Schumaker@xxxxxxxxxx>

This allows us to have an in-kernel copy mechanism that avoids frequent
switches between kernel and user space.  This is especially useful so
NFSD can support server-side copies.

The default (flags=0) means to first attempt copy acceleration, but use
the pagecache if that fails.

I moved the rw_verify_area() calls into the fallback code since some
filesystems can handle reflinking a large range.

Signed-off-by: Anna Schumaker <Anna.Schumaker@xxxxxxxxxx>
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Reviewed-by: Padraig Brady <P@xxxxxxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
---
 fs/read_write.c |   13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)


diff --git a/fs/read_write.c b/fs/read_write.c
index 97c15ca..6f73af1 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1354,8 +1354,7 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t 
pos_in,
 
        if (!(file_in->f_mode & FMODE_READ) ||
            !(file_out->f_mode & FMODE_WRITE) ||
-           (file_out->f_flags & O_APPEND) ||
-           !file_out->f_op->copy_file_range)
+           (file_out->f_flags & O_APPEND))
                return -EBADF;
 
        /* this could be relaxed once a method supports cross-fs copies */
@@ -1369,8 +1368,14 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t 
pos_in,
        if (ret)
                return ret;
 
-       ret = file_out->f_op->copy_file_range(file_in, pos_in, file_out, 
pos_out,
-                                             len, flags);
+       ret = -EOPNOTSUPP;
+       if (file_out->f_op->copy_file_range)
+               ret = file_out->f_op->copy_file_range(file_in, pos_in, file_out,
+                                                     pos_out, len, flags);
+       if (ret == -EOPNOTSUPP)
+               ret = do_splice_direct(file_in, &pos_in, file_out, &pos_out,
+                               len > MAX_RW_COUNT ? MAX_RW_COUNT : len, 0);
+
        if (ret > 0) {
                fsnotify_access(file_in);
                add_rchar(current, ret);