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

[Jeff Layton <jlayton@kernel.org>]

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...

> 
> > 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 |		\
> 
> 

-- 
Jeff Layton <jlayton@kernel.org>