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>
diff --git a/mdopen.c b/mdopen.c
index fe240e5..82b97fc 100644
--- a/mdopen.c
+++ b/mdopen.c
@@ -313,6 +313,18 @@
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) {
