Over NFS, an open() call could result in multiple over-the-wire

GETATTRs being generated - one from lookup()/namei() and the other
from nfs_open() (for cto consistency). This change eliminates the
GETATTR in nfs_open() if an otw GETATTR was done from the namei()
path. Instead of extending the vop interface, we timestamp each attr
load, and use this to detect whether a GETATTR was done from namei()
for this syscall. Introduces a thread-local variable that counts the
syscalls made by the thread and uses <pid, tid, thread syscalls> as
the attrload timestamp. Thanks to jhb@ and peter@ for a discussion on
thread state that could be used as the timestamp with minimal overhead.

1 files changed, 10 insertions, 1 deletions

diff --git a/sys/nfsclient/nfs_vnops.c b/sys/nfsclient/nfs_vnops.c
index 761618b..55d7b3f 100644
--- a/sys/nfsclient/nfs_vnops.c
+++ b/sys/nfsclient/nfs_vnops.c
@@ -432,6 +432,8 @@ nfs_access(struct vop_access_args *ap)
 	}
 }
 
+int nfs_otw_getattr_avoid = 0;
+
 /*
  * nfs open vnode op
  * Check to see if the type is ok
@@ -471,7 +473,14 @@ nfs_open(struct vop_open_args *ap)
 		np->n_mtime = vattr.va_mtime;
 		mtx_unlock(&np->n_mtx);
 	} else {
-		np->n_attrstamp = 0;
+		struct thread *td = curthread;
+
+		if (np->n_ac_ts_syscalls != td->td_syscalls ||
+		    np->n_ac_ts_tid != td->td_tid || 
+		    td->td_proc == NULL ||
+		    np->n_ac_ts_pid != td->td_proc->p_pid) {
+			np->n_attrstamp = 0;
+		}
 		mtx_unlock(&np->n_mtx);						
 		error = VOP_GETATTR(vp, &vattr, ap->a_cred, ap->a_td);
 		if (error)