From e19a872c2b378458e72cab6c5ac30b12efad13f0 Mon Sep 17 00:00:00 2001
From: Geoffrey Challen <challen@buffalo.edu>
Date: Sat, 5 Mar 2016 08:46:00 -0500
Subject: [PATCH] Static thread names.

---
 kern/include/thread.h      | 12 +++++++++++-
 kern/test/threadlisttest.c |  6 +-----
 kern/thread/thread.c       | 12 +++++-------
 3 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/kern/include/thread.h b/kern/include/thread.h
index 48ca76d..42d56b4 100644
--- a/kern/include/thread.h
+++ b/kern/include/thread.h
@@ -48,6 +48,7 @@ struct cpu;
 
 /* Size of kernel stacks; must be power of 2 */
 #define STACK_SIZE 4096
+#define MAX_NAME_LENGTH 64
 
 /* Mask for extracting the stack base address of a kernel stack pointer */
 #define STACK_MASK  (~(vaddr_t)(STACK_SIZE-1))
@@ -70,7 +71,16 @@ struct thread {
 	 * These go up front so they're easy to get to even if the
 	 * debugger is messed up.
 	 */
-	char *t_name;			/* Name of this thread */
+
+	/*
+	 * Name of this thread. Used to be dynamically allocated using kmalloc, but
+	 * this can cause small changes in the amount of available memory due to the
+	 * fact that it was cleaned up in exorcise. This produces more predictable
+	 * behavior at the cost of a small amount of memory overhead and the
+	 * inability to give threads huge names.
+	 */
+
+	char t_name[MAX_NAME_LENGTH];
 	const char *t_wchan_name;	/* Name of wait channel, if sleeping */
 	threadstate_t t_state;		/* State this thread is in */
 
diff --git a/kern/test/threadlisttest.c b/kern/test/threadlisttest.c
index 993ee01..dd96bd5 100644
--- a/kern/test/threadlisttest.c
+++ b/kern/test/threadlisttest.c
@@ -66,10 +66,7 @@ fakethread_create(const char *name)
 	}
 	/* ignore most of the fields, zero everything for tidiness */
 	bzero(t, sizeof(*t));
-	t->t_name = kstrdup(name);
-	if (t->t_name == NULL) {
-		panic("threadlisttest: Out of memory\n");
-	}
+	strcpy(t->t_name, name);
 	t->t_stack = FAKE_MAGIC;
 	threadlistnode_init(&t->t_listnode, t);
 	return t;
@@ -84,7 +81,6 @@ fakethread_destroy(struct thread *t)
 {
 	KASSERT(t->t_stack == FAKE_MAGIC);
 	threadlistnode_cleanup(&t->t_listnode);
-	kfree(t->t_name);
 	kfree(t);
 }
 
diff --git a/kern/thread/thread.c b/kern/thread/thread.c
index 13d8ee0..d21388f 100644
--- a/kern/thread/thread.c
+++ b/kern/thread/thread.c
@@ -119,17 +119,16 @@ thread_create(const char *name)
 	struct thread *thread;
 
 	DEBUGASSERT(name != NULL);
+	if (strlen(name) > MAX_NAME_LENGTH) {
+		return NULL;
+	}
 
 	thread = kmalloc(sizeof(*thread));
 	if (thread == NULL) {
 		return NULL;
 	}
 
-	thread->t_name = kstrdup(name);
-	if (thread->t_name == NULL) {
-		kfree(thread);
-		return NULL;
-	}
+	strcpy(thread->t_name, name);
 	thread->t_wchan_name = "NEW";
 	thread->t_state = S_READY;
 
@@ -280,7 +279,6 @@ thread_destroy(struct thread *thread)
 	/* sheer paranoia */
 	thread->t_wchan_name = "DESTROYED";
 
-	kfree(thread->t_name);
 	kfree(thread);
 }
 
@@ -795,7 +793,7 @@ thread_exit(void)
 	thread_checkstack(cur);
 
 	/* Interrupts off on this processor */
-        splhigh();
+	splhigh();
 	thread_switch(S_ZOMBIE, NULL, NULL);
 	panic("braaaaaaaiiiiiiiiiiinssssss\n");
 }