On Fri, 24 May 2013, Yan, Zheng wrote:
> On 05/24/2013 06:58 AM, Sage Weil wrote:
> > On Thu, 23 May 2013, Yan, Zheng wrote:
> > [snip]
> >> +
> >> +void CInode::store_backtrace(Context *fin)
> >> +{
> >> + dout(10) << "store_backtrace on " << *this << dendl;
> >> + assert(is_dirty_parent());
> >> +
> >> + auth_pin(this);
> >> +
> >> + int64_t pool;
> >> + if (is_dir())
> >> + pool = mdcache->mds->mdsmap->get_metadata_pool();
> >> + else
> >> + pool = inode.layout.fl_pg_pool;
> >> +
> >> + inode_backtrace_t bt;
> >> + build_backtrace(pool, &bt);
> >> + bufferlist bl;
> >> + ::encode(bt, bl);
> >> +
> >> + // write it.
> >> + SnapContext snapc;
> >> + object_t oid = get_object_name(ino(), frag_t(), "");
> >> + object_locator_t oloc(pool);
> >> + Context *fin2 = new C_Inode_StoredBacktrace(this,
> >> inode.backtrace_version, fin);
> >> +
> >> + if (!state_test(STATE_DIRTYPOOL)) {
> >> + mdcache->mds->objecter->setxattr(oid, oloc, "parent", snapc, bl,
> >> + ceph_clock_now(g_ceph_context),
> >> + 0, NULL, fin2);
> >> + return;
> >> + }
> >> +
> >> + C_GatherBuilder gather(g_ceph_context, fin2);
> >> + mdcache->mds->objecter->setxattr(oid, oloc, "parent", snapc, bl,
> >> + ceph_clock_now(g_ceph_context),
> >> + 0, NULL, gather.new_sub());
> >> + for (set<int64_t>::iterator p = bt.old_pools.begin();
> >> + p != bt.old_pools.end();
> >> + ++p) {
> >> + object_locator_t oloc2(*p);
> >> + mdcache->mds->objecter->setxattr(oid, oloc2, "parent", snapc, bl,
> >> + ceph_clock_now(g_ceph_context),
> >> + 0, NULL, gather.new_sub());
> >> + }
> >
> > I think for both of theese operations we need an ObjectWriteOperation that
> > does a touch() and then tsetxattr to ensure the object actually exists.
> >
> will add it
>
> > Also, if one mds has a backtrace write in flight, exports teh inode, and
> > the second mds needs to update it, we need to make sure they don't race
> > and overwrite a newer trace with an older one. That could be done with a
> > parent_version xattr with the backttrace_version in it and a generic rados
> > cmpxattr guard, I believe. Even then we may race with an unlink, but that
> > may be something we just tolerate...
> >
> my code calls auth_pin() in CInode::store_backtrace(). I think it also avoid
> the race.
even better. sounds good!
sage
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