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.
Regards
Yan, Zheng
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