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

[Xiubo Li <xiubli@xxxxxxxxxx>]

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@xxxxxxxxxx wrote:
> > > > From: Xiubo Li <xiubli@xxxxxxxxxx>
> > > >
> > > > 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@xxxxxxxxxx>
> > > > ---
> > > >    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 |		\