Why "splice" doesn't splice between two non-pipes?

[Askar Safin <safinaskar@xxxxxxx>]

Why "splice" doesn't splice between two non-pipes? I think such splice would be very useful (not only file-to-socket). For example, for dd, cp, cp -r. Also, it seems, the kernel already supports splice between non-pipes (do_splice_direct function), this function is just not available to userspace. (The patch is just an idea, not tested. I don't know how to actually add this feature.)

==
Askar Safin

diff --git a/fs/splice.c b/fs/splice.c
index d37431d..ffb95db 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1394,7 +1394,7 @@ static long do_splice(struct file *in, loff_t __user *off_in,
                return ret;
        }
 
-       return -EINVAL;
+       return do_splice_direct(in, off_in, out, off_out, len, flags);
 }
 
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