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, 2 insertions, 0 deletions

diff --git a/sys/i386/i386/trap.c b/sys/i386/i386/trap.c
index 409ac0a..cf25f9f 100644
--- a/sys/i386/i386/trap.c
+++ b/sys/i386/i386/trap.c
@@ -996,6 +996,8 @@ syscall(struct trapframe *frame)
 	CTR4(KTR_SYSC, "syscall enter thread %p pid %d proc %s code %d", td,
 	    td->td_proc->p_pid, td->td_proc->p_comm, code);
 
+	td->td_syscalls++;
+
 	if (error == 0) {
 		td->td_retval[0] = 0;
 		td->td_retval[1] = frame->tf_edx;