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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>
This commit is contained in:
NeilBrown 2017-04-12 16:29:04 +10:00 committed by Jes Sorensen
parent 46a533a90c
commit 039df36231
1 changed files with 12 additions and 0 deletions
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12
mdopen.c
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@ -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) {