Re: [PATCH] ceph: add 'noshare' mount option support

[Xiubo Li <xiubli@redhat.com>]

On 2020/10/13 21:41, Jeff Layton wrote:
> On Tue, 2020-10-13 at 20:44 +0800, Xiubo Li wrote:
>> On 2020/10/13 20:31, Jeff Layton wrote:
>>> On Tue, 2020-10-13 at 18:31 +0800, xiubli@redhat.com wrote:
>>>> From: Xiubo Li <xiubli@redhat.com>
>>>>
>>>> This will disable different mount points to share superblocks.
>>>>
>>> Why? What problem does this solve? Don't make us dig through random
>>> tracker bugs to determine this, please. :)
>> So, should we just mannully trigger to crash the kernel to get the
>> coredump ?
>>
> Looking at the tracker ticket, it looks like you want this to work
> around some issues with lazy unmounts in tests.  If so, then sure,
> forcing a coredump might give you an indication of what happened.
>
> In general though, this sounds like a hacky workaround for the problem
> in that tracker. I suggest we don't do this and work toward solving the
> real problems that caused the test writers to use lazy umounts in the
> first place...

Okay, will try this.

Thanks.


>>> Also, the subject mentions a "noshare" mount option, but the code below
>>> will be expecting sharesb/nosharesb.
>>>
>>>> URL: https://tracker.ceph.com/issues/46883
>>>> Signed-off-by: Xiubo Li <xiubli@redhat.com>
>>>> ---
>>>>    fs/ceph/super.c | 12 ++++++++++++
>>>>    fs/ceph/super.h |  1 +
>>>>    2 files changed, 13 insertions(+)
>>>>
>>>> diff --git a/fs/ceph/super.c b/fs/ceph/super.c
>>>> index 2f530a111b3a..6f283e4d62ee 100644
>>>> --- a/fs/ceph/super.c
>>>> +++ b/fs/ceph/super.c
>>>> @@ -159,6 +159,7 @@ enum {
>>>>    	Opt_quotadf,
>>>>    	Opt_copyfrom,
>>>>    	Opt_wsync,
>>>> +	Opt_sharesb,
>>>>    };
>>>>    
>>>>    enum ceph_recover_session_mode {
>>>> @@ -199,6 +200,7 @@ static const struct fs_parameter_spec ceph_mount_parameters[] = {
>>>>    	fsparam_string	("source",			Opt_source),
>>>>    	fsparam_u32	("wsize",			Opt_wsize),
>>>>    	fsparam_flag_no	("wsync",			Opt_wsync),
>>>> +	fsparam_flag_no	("sharesb",			Opt_sharesb),
>>>>    	{}
>>>>    };
>>>>    
>>>> @@ -455,6 +457,12 @@ static int ceph_parse_mount_param(struct fs_context *fc,
>>>>    		else
>>>>    			fsopt->flags |= CEPH_MOUNT_OPT_ASYNC_DIROPS;
>>>>    		break;
>>>> +	case Opt_sharesb:
>>>> +		if (!result.negated)
>>>> +			fsopt->flags &= ~CEPH_MOUNT_OPT_NO_SHARE_SB;
>>>> +		else
>>>> +			fsopt->flags |= CEPH_MOUNT_OPT_NO_SHARE_SB;
>>>> +		break;
>>>>    	default:
>>>>    		BUG();
>>>>    	}
>>>> @@ -1007,6 +1015,10 @@ static int ceph_compare_super(struct super_block *sb, struct fs_context *fc)
>>>>    
>>>>    	dout("ceph_compare_super %p\n", sb);
>>>>    
>>>> +	if (fsopt->flags & CEPH_MOUNT_OPT_NO_SHARE_SB ||
>>>> +	    other->mount_options->flags & CEPH_MOUNT_OPT_NO_SHARE_SB)
>>>> +		return 0;
>>>> +
>>>>    	if (compare_mount_options(fsopt, opt, other)) {
>>>>    		dout("monitor(s)/mount options don't match\n");
>>>>    		return 0;
>>>> diff --git a/fs/ceph/super.h b/fs/ceph/super.h
>>>> index f097237a5ad3..e877c21196e5 100644
>>>> --- a/fs/ceph/super.h
>>>> +++ b/fs/ceph/super.h
>>>> @@ -44,6 +44,7 @@
>>>>    #define CEPH_MOUNT_OPT_NOQUOTADF       (1<<13) /* no root dir quota in statfs */
>>>>    #define CEPH_MOUNT_OPT_NOCOPYFROM      (1<<14) /* don't use RADOS 'copy-from' op */
>>>>    #define CEPH_MOUNT_OPT_ASYNC_DIROPS    (1<<15) /* allow async directory ops */
>>>> +#define CEPH_MOUNT_OPT_NO_SHARE_SB     (1<<16) /* disable sharing the same superblock */
>>>>    
>>>>    #define CEPH_MOUNT_OPT_DEFAULT			\
>>>>    	(CEPH_MOUNT_OPT_DCACHE |		\
>>