[RFC PATCH 1/7] NFSD: Async COPY result needs to return a write verifier

[cel@xxxxxxxxxx]

From: Chuck Lever <chuck.lever@xxxxxxxxxx>

Currently, when NFSD handles an asynchronous COPY, it returns a
zero write verifier, relying on the subsequent CB_OFFLOAD callback
to pass the write verifier and a stable_how4 value to the client.

However, if the CB_OFFLOAD never arrives at the client (for example,
if a network partition occurs just as the server sends the
CB_OFFLOAD operation), the client will never receive this verifier.
Thus, if the client sends a follow-up COMMIT, there is no way for
the client to assess the COMMIT result.

The usual recovery for a missing CB_OFFLOAD is for the client to
send an OFFLOAD_STATUS operation, but that operation does not carry
a write verifier in its result. Neither does it carry a stable_how4
value, so the client /must/ send a COMMIT in this case -- which will
always fail because currently there's still no write verifier in the
COPY result.

Thus the server needs to return a normal write verifier in its COPY
result even if the COPY operation is to be performed asynchronously.

If the server recognizes the callback stateid in subsequent
OFFLOAD_STATUS operations, then obviously it has not restarted, and
the write verifier the client received in the COPY result is still
valid and can be used to assess a COMMIT of the copied data, if one
is needed.

Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
 fs/nfsd/nfs4proc.c | 25 +++++++++----------------
 1 file changed, 9 insertions(+), 16 deletions(-)

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 2e39cf2e502a..60c526adc27c 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -751,15 +751,6 @@ nfsd4_access(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 			   &access->ac_supported);
 }
 
-static void gen_boot_verifier(nfs4_verifier *verifier, struct net *net)
-{
-	__be32 *verf = (__be32 *)verifier->data;
-
-	BUILD_BUG_ON(2*sizeof(*verf) != sizeof(verifier->data));
-
-	nfsd_copy_write_verifier(verf, net_generic(net, nfsd_net_id));
-}
-
 static __be32
 nfsd4_commit(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	     union nfsd4_op_u *u)
@@ -1630,7 +1621,6 @@ static void nfsd4_init_copy_res(struct nfsd4_copy *copy, bool sync)
 		test_bit(NFSD4_COPY_F_COMMITTED, &copy->cp_flags) ?
 			NFS_FILE_SYNC : NFS_UNSTABLE;
 	nfsd4_copy_set_sync(copy, sync);
-	gen_boot_verifier(&copy->cp_res.wr_verifier, copy->cp_clp->net);
 }
 
 static ssize_t _nfsd_copy_file_range(struct nfsd4_copy *copy,
@@ -1803,9 +1793,11 @@ static __be32
 nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 		union nfsd4_op_u *u)
 {
-	struct nfsd4_copy *copy = &u->copy;
-	__be32 status;
+	struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
 	struct nfsd4_copy *async_copy = NULL;
+	struct nfsd4_copy *copy = &u->copy;
+	struct nfsd42_write_res *result;
+	__be32 status;
 
 	/*
 	 * Currently, async COPY is not reliable. Force all COPY
@@ -1814,6 +1806,9 @@ nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	 */
 	nfsd4_copy_set_sync(copy, true);
 
+	result = &copy->cp_res;
+	nfsd_copy_write_verifier((__be32 *)&result->wr_verifier.data, nn);
+
 	copy->cp_clp = cstate->clp;
 	if (nfsd4_ssc_is_inter(copy)) {
 		trace_nfsd_copy_inter(copy);
@@ -1838,8 +1833,6 @@ nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	memcpy(&copy->fh, &cstate->current_fh.fh_handle,
 		sizeof(struct knfsd_fh));
 	if (nfsd4_copy_is_async(copy)) {
-		struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
-
 		status = nfserrno(-ENOMEM);
 		async_copy = kzalloc(sizeof(struct nfsd4_copy), GFP_KERNEL);
 		if (!async_copy)
@@ -1851,8 +1844,8 @@ nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 			goto out_err;
 		if (!nfs4_init_copy_state(nn, copy))
 			goto out_err;
-		memcpy(&copy->cp_res.cb_stateid, &copy->cp_stateid.cs_stid,
-			sizeof(copy->cp_res.cb_stateid));
+		memcpy(&result->cb_stateid, &copy->cp_stateid.cs_stid,
+			sizeof(result->cb_stateid));
 		dup_copy_fields(copy, async_copy);
 		async_copy->copy_task = kthread_create(nfsd4_do_async_copy,
 				async_copy, "%s", "copy thread");
-- 
2.46.0