NFSv4: Add functions to order RPC calls

 NFSv4 file state-changing functions such as OPEN, CLOSE, LOCK,... are all
 labelled with "sequence identifiers" in order to prevent the server from
 reordering RPC requests, as this could cause its file state to
 become out of sync with the client.

 Currently the NFS client code enforces this ordering locally using
 semaphores to restrict access to structures until the RPC call is done.
 This, of course, only works with synchronous RPC calls, since the
 user process must first grab the semaphore.
 By dropping semaphores, and instead teaching the RPC engine to hold
 the RPC calls until they are ready to be sent, we can extend this
 process to work nicely with asynchronous RPC calls too.

 This patch adds a new list called "rpc_sequence" that defines the order
 of the RPC calls to be sent. We add one such list for each state_owner.
 When an RPC call is ready to be sent, it checks if it is top of the
 rpc_sequence list. If so, it proceeds. If not, it goes back to sleep,
 and loops until it hits top of the list.
 Once the RPC call has completed, it can then bump the sequence id counter,
 and remove itself from the rpc_sequence list, and then wake up the next
 sleeper.

 Note that the state_owner sequence ids and lock_owner sequence ids are
 all indexed to the same rpc_sequence list, so OPEN, LOCK,... requests
 are all ordered w.r.t. each other.

 Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 8 insertions, 7 deletions

diff --git a/include/linux/nfs_xdr.h b/include/linux/nfs_xdr.h
index a2bf6914ff1b..d578912bf9a9 100644
--- a/include/linux/nfs_xdr.h
+++ b/include/linux/nfs_xdr.h
@@ -96,12 +96,13 @@ struct nfs4_change_info {
         u64                     after;
 };
 
+struct nfs_seqid;
 /*
  * Arguments to the open call.
  */
 struct nfs_openargs {
         const struct nfs_fh *   fh;
-        __u32                   seqid;
+        struct nfs_seqid *      seqid;
         int                     open_flags;
         __u64                   clientid;
         __u32                   id;
@@ -136,7 +137,7 @@ struct nfs_openres {
 struct nfs_open_confirmargs {
         const struct nfs_fh *   fh;
         nfs4_stateid            stateid;
-        __u32                   seqid;
+        struct nfs_seqid *      seqid;
 };
 
 struct nfs_open_confirmres {
@@ -149,7 +150,7 @@ struct nfs_open_confirmres {
 struct nfs_closeargs {
         struct nfs_fh *         fh;
         nfs4_stateid            stateid;
-        __u32                   seqid;
+        struct nfs_seqid *      seqid;
         int                     open_flags;
 };
 
@@ -165,15 +166,15 @@ struct nfs_lowner {
 };
 
 struct nfs_open_to_lock {
-        __u32                   open_seqid;
+        struct nfs_seqid *      open_seqid;
         nfs4_stateid            open_stateid;
-        __u32                   lock_seqid;
+        struct nfs_seqid *      lock_seqid;
         struct nfs_lowner       lock_owner;
 };
 
 struct nfs_exist_lock {
         nfs4_stateid            stateid;
-        __u32                   seqid;
+        struct nfs_seqid *      seqid;
 };
 
 struct nfs_lock_opargs {
@@ -186,7 +187,7 @@ struct nfs_lock_opargs {
 };
 
 struct nfs_locku_opargs {
-        __u32                   seqid;
+        struct nfs_seqid *      seqid;
         nfs4_stateid            stateid;
 };