sys_sendfile: switch to using ->splice_read, if available

This patch makes sendfile prefer to use ->splice_read(), if it's
available in the file_operations structure.

Signed-off-by: Jens Axboe <[e-mail]>

fs/read_write.c

···
 #include <linux/module.h>
 #include <linux/syscalls.h>
 #include <linux/pagemap.h>
+#include <linux/pipe_fs_i.h>
 #include "read_write.h"
 
 #include <asm/uaccess.h>
···
 	.read		= do_sync_read,
 	.aio_read	= generic_file_aio_read,
 	.mmap		= generic_file_readonly_mmap,
-	.sendfile	= generic_file_sendfile,
+	.splice_read	= generic_file_splice_read,
 };
 
 EXPORT_SYMBOL(generic_ro_fops);
···
 	struct inode * in_inode, * out_inode;
 	loff_t pos;
 	ssize_t retval;
-	int fput_needed_in, fput_needed_out;
+	int fput_needed_in, fput_needed_out, fl;
 
 	/*
 	 * Get input file, and verify that it is ok..
···
 	in_inode = in_file->f_path.dentry->d_inode;
 	if (!in_inode)
 		goto fput_in;
-	if (!in_file->f_op || !in_file->f_op->sendfile)
+	if (!in_file->f_op || (!in_file->f_op->sendfile &&
+	    !in_file->f_op->splice_read))
 		goto fput_in;
 	retval = -ESPIPE;
 	if (!ppos)
···
 		count = max - pos;
 	}
 
-	retval = in_file->f_op->sendfile(in_file, ppos, count, file_send_actor, out_file);
+	if (in_file->f_op->splice_read) {
+		fl = 0;
+#if 0
+		/*
+		 * We need to debate whether we can enable this or not. The
+		 * man page documents EAGAIN return for the output at least,
+		 * and the application is arguably buggy if it doesn't expect
+		 * EAGAIN on a non-blocking file descriptor.
+		 */
+		if (in_file->f_flags & O_NONBLOCK)
+			fl = SPLICE_F_NONBLOCK;
+#endif
+		retval = do_splice_direct(in_file, ppos, out_file, count, fl);
+	} else
+		retval = in_file->f_op->sendfile(in_file, ppos, count, file_send_actor, out_file);
 
 	if (retval > 0) {
 		add_rchar(current, retval);