From 039df36231335fabe4da1a22fa3accb160d8bc1b Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb@suse.com>
Date: Wed, 12 Apr 2017 16:29:04 +1000
Subject: [RHEL7.5 PATCH 072/169] mdopen: use parameters/new_array to
 create arrays whenever possible.

In a sufficiently recent kernel, an md%d array can be
created by writing to .../parameters/new_array.
If mdadm does this consistently, then another new
feature, disabling create_on_open, can be enabled.
This avoids races on shutdown.

An added benefit of using new_array (where available)
is that it allows md arrays with numbers larger than 511
(e.g. md999) to be created.  The old create_on_open
mechanism doesn't support such devices since
Commit: af5628f05db6 ("md: disable probing for md devices 512 and over.")
in Linux 3.17.

After a few more mdadm releases it would be good to
have mdadm disable create_on_open automatically.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Jes Sorensen <jsorensen@fb.com>
---
 mdopen.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/mdopen.c b/mdopen.c
index fe240e5..82b97fc 100644
--- a/mdopen.c
+++ b/mdopen.c
@@ -313,6 +313,18 @@ int create_mddev(char *dev, char *name, int autof, int trustworthy,
 		if (n < 0)
 			devnm[0] = 0;
 	}
+	if (num >= 0) {
+		int fd;
+		int n = -1;
+		sprintf(devnm, "md%d", num);
+		fd = open("/sys/module/md_mod/parameters/new_array", O_WRONLY);
+		if (fd >= 0) {
+			n = write(fd, devnm, strlen(devnm));
+			close(fd);
+		}
+		if (n < 0)
+			devnm[0] = 0;
+	}
 	if (devnm[0])
 		;
 	else if (num < 0) {
-- 
2.7.4