Generalised support for copy-on-write structures shared by threads.

Thread credentials are maintained as follows: each thread has a pointer to
creds and a reference on them. The pointer is compared with proc's creds on
userspace<->kernel boundary and updated if needed.

This patch introduces a counter which can be compared instead, so that more
structures can use this scheme without adding more comparisons on the boundary.

1 files changed, 3 insertions, 3 deletions

diff --git a/sys/kern/kern_thr.c b/sys/kern/kern_thr.c
index 6cd215e..e6b0a59 100644
--- a/sys/kern/kern_thr.c
+++ b/sys/kern/kern_thr.c
@@ -220,13 +220,13 @@ create_thread(struct thread *td, mcontext_t *ctx,
 	bcopy(&td->td_startcopy, &newtd->td_startcopy,
 	    __rangeof(struct thread, td_startcopy, td_endcopy));
 	newtd->td_proc = td->td_proc;
-	newtd->td_ucred = crhold(td->td_ucred);
+	thread_cow_get(newtd, td);
 
 	if (ctx != NULL) { /* old way to set user context */
 		error = set_mcontext(newtd, ctx);
 		if (error != 0) {
+			thread_cow_free(newtd);
 			thread_free(newtd);
-			crfree(td->td_ucred);
 			goto fail;
 		}
 	} else {
@@ -238,8 +238,8 @@ create_thread(struct thread *td, mcontext_t *ctx,
 		/* Setup user TLS address and TLS pointer register. */
 		error = cpu_set_user_tls(newtd, tls_base);
 		if (error != 0) {
+			thread_cow_free(newtd);
 			thread_free(newtd);
-			crfree(td->td_ucred);
 			goto fail;
 		}
 	}