mdadm: one question about the readonly and readwrite feature

[Zhilong Liu <zlliu@xxxxxxxx>]

Hi, Neil;

  Excuse me, according to read 'mdadm/tests/ToTest', I'm a little 
confused about "readonly"
and "readwrite" feature, and I've no idea how to fix it. Thus I report 
this question and I'm sorry
for this long description email.

relevant linux/driver/md commit: 260fa034ef7a4ff8b73068b48ac497edd5217491

  My question: If the array has been set the MD_CLOSING flag, although 
hasn't removed the sysfs
folder because sysfs_remove_group() wasn't invoked, and now, how should 
mdadm continue to
control this 'readonly' array?
  Of course, once we cannot operate the array, the 'readwrite' feature 
would be never worked.

Test step:
# ./mdadm -CR /dev/md0 -b internal -l1 -n2 /dev/loop[0-1] --assume-clean
# ./mdadm -o /dev/mdX

# in md.h
enum mddev_flags {
        MD_ARRAY_FIRST_USE,     /* First use of array, needs 
initialization */
        MD_CLOSING,             /* If set, we are closing the array, do 
not open it then */

1. In mdadm tool:
  the func: Manage_ro(dv->devname, mdfd, -1) would be never invoked 
once the array has been
set 'readonly' before. the open_mddev() cannot get a valid file 
descriptor any more. Most of mdadm
commands would be failure, I have to execute the "echo clear > 
/sys/block/mdX/md/array_state".

# refer to mdadm.c
... ...
static int misc_list(struct mddev_dev *devlist,
                     struct mddev_ident *ident,
                     char *dump_directory,
                     struct supertype *ss, struct context *c)
{
... ...
                switch(dv->devname[0] == '/') {
                        case 0:
                                mdfd = open_dev(dv->devname);
                                if (mdfd >= 0) break;
                        case 1:
                                mdfd = open_mddev(dv->devname, 1);
                }
                if (mdfd>=0) {
                        switch(dv->disposition) {
                        case 'R':
                                c->runstop = 1;
                                rv |= Manage_run(dv->devname, mdfd, c); 
break;
                        case 'S':
                                rv |= Manage_stop(dv->devname, mdfd, 
c->verbose, 0); break;
                        case 'o':
                                rv |= Manage_ro(dv->devname, mdfd, 1); 
break;
                        case 'w':
                                rv |= Manage_ro(dv->devname, mdfd, -1); 
break;
                        }
2. in md driver:
For readonly, the code path is:
ioctl(fd, STOP_ARRAY_RO, NULL)  - - > set_bit(MD_CLOSING, &mddev->flags) 
- - > md_set_readonly()

cut a piece of code: - -> md_set_readonly() of md.c:
... ...
        if (mddev->pers) {
                __md_stop_writes(mddev);

                err  = -ENXIO;
                if (mddev->ro==1)
                        goto out;
                mddev->ro = 1;
                set_disk_ro(mddev->gendisk, 1);
                clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
                set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);   - - > 
I think it did nothing once readonly has been set.
                md_wakeup_thread(mddev->thread);
                sysfs_notify_dirent_safe(mddev->sysfs_state);
                err = 0;
... ...

Thanks for your patience,
-Zhilong
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