On 10/11/2017 04:16 AM, NeilBrown wrote:

On Tue, Oct 10 2017, Zhilong Liu wrote:

quoted

On 09/25/2017 01:52 PM, NeilBrown wrote:

quoted

Creating an array by opening a block-device with major number of 9
will transparently load the md module if needed.
Creating an array by opening
     /sys/module/md_mod/parameters/new_array
and writing to it won't, it will just fail if md_mod isn't loaded.

So when opening that file fails with ENOENT, run "modprobe md_mod" and
try again.

This fixes a bug whereby if you have "CREATE names=yes" in mdadm.conf,
and the md modules isn't loaded, then creating or assembling an
array will not honor the "names=yes" configuration.

Signed-off-by: NeilBrown <redacted>
---
   mdopen.c | 4 ++++
   1 file changed, 4 insertions(+)

diff --git a/mdopen.c b/mdopen.c
index 3c0052f2db23..dcdc6f23e6c1 100644
--- a/mdopen.c
+++ b/mdopen.c

@@ -312,6 +312,10 @@ int create_mddev(char *dev, char *name, int autof, int trustworthy,
   		if (block_udev)
   			udev_block(devnm);
   		fd = open("/sys/module/md_mod/parameters/new_array", O_WRONLY);
+		if (fd < 0 && errno == ENOENT) {
+			system("modprobe md_mod");

[nip]

Hmmm.. that's annoying.  I wonder why "system" is marked
"warn_unused_result".

in /usr/include/stdlib.h:
...
712 /* Execute the given line as a shell command.
713
714    This function is a cancellation point and therefore not marked with
715    __THROW.  */
716 extern int system (const char *__command) __wur;
...

the "warn_unused_result" is from the __wur parameter, re-compile mdadm 
after delete the '__wur',
it works.

In this case I really don't care - I'm not convinced an extra error
message will really help.
Maybe
    if (system("modprobe md_mod") == 0)
         fd = open("/sys/......", O_WRONLY);

Agree.

We do what a better error message, then it should be based on 'fd < 0'.
e.g.
   if (fd < 0 || n != strlen(devnm))
       pr_err("Fail create array using /sys/module/md_mod/parameters/new_array\n");

you mean something like this?

diff --git a/mdopen.c b/mdopen.c
index dcdc6f2..9de347e 100644
--- a/mdopen.c
+++ b/mdopen.c

@@ -313,14 +313,17 @@ int create_mddev(char *dev, char *name, int autof, 

int trustworthy,
                         udev_block(devnm);
                 fd = open("/sys/module/md_mod/parameters/new_array", 
O_WRONLY);
                 if (fd < 0 && errno == ENOENT) {
-                       system("modprobe md_mod");
-                       fd = 
open("/sys/module/md_mod/parameters/new_array", O_WRONLY);
+                       if (system("modprobe md_mod") == 0)
+                               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) {
+               if (fd < 0 || n != strlen(devnm)) {
+                       pr_err("Fail create array using "
+ "/sys/module/md_mod/parameters/new_array\n");
                         devnm[0] = 0;
                         udev_unblock();
                 }


Thanks,
-Zhilong

Thanks,
NeilBrown