From 607fb6bf7ff8279b2cce75f817679c8e25b01ffb Mon Sep 17 00:00:00 2001
From: Ben Gras <ben@minix3.org>
Date: Tue, 27 Jun 2006 12:19:45 +0000
Subject: [PATCH] Add a flag to grants system indicating a slot is VALID; so a
 slot can be reserved (USED), while toggling VALID on and off.

---
 include/minix/safecopies.h  |  2 ++
 kernel/system/do_safecopy.c |  4 ++--
 lib/syslib/safecopies.c     | 18 +++++++++++++++---
 3 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/include/minix/safecopies.h b/include/minix/safecopies.h
index 083c7d979..53366e1d2 100644
--- a/include/minix/safecopies.h
+++ b/include/minix/safecopies.h
@@ -62,6 +62,7 @@ struct vscp_vec {
 #define CPF_DIRECT	0x000200 /* Grant from this process to another. */
 #define CPF_INDIRECT	0x000400 /* Grant from grant to another. */
 #define CPF_MAGIC	0x000800 /* Grant from any to any. */
+#define CPF_VALID	0x001000 /* Grant slot contains valid grant. */
 
 /* Prototypes for functions in libsys. */
 _PROTOTYPE( cp_grant_id_t cpf_grant_direct, (endpoint_t, vir_bytes, size_t, int));
@@ -78,6 +79,7 @@ _PROTOTYPE( int cpf_setgrant_indirect, (cp_grant_id_t g, endpoint_t who_to,
 	endpoint_t who_from, cp_grant_id_t his_g));
 _PROTOTYPE( int cpf_setgrant_magic, (cp_grant_id_t g, endpoint_t who_to,
 	endpoint_t who_from, vir_bytes addr, size_t bytes, int access));
+_PROTOTYPE( int cpf_setgrant_disable, (cp_grant_id_t grant_id));
 
 /* Set a process' grant table location and size (in-kernel only). */
 #define _K_SET_GRANT_TABLE(rp, ptr, entries)	\
diff --git a/kernel/system/do_safecopy.c b/kernel/system/do_safecopy.c
index 0d46a96fa..41e3a7968 100644
--- a/kernel/system/do_safecopy.c
+++ b/kernel/system/do_safecopy.c
@@ -90,8 +90,8 @@ endpoint_t *e_granter;		/* new granter (magic grants) */
 	phys_copy(phys_grant, vir2phys(&g), sizeof(g));
 
 	/* Check validity. */
-	if(!(g.cp_flags & CPF_USED)) {
-		kprintf("grant verify failed: invalid\n");
+	if((g.cp_flags & (CPF_USED | CPF_VALID)) != (CPF_USED | CPF_VALID)) {
+		kprintf("grant verify failed: unused or invalid\n");
 		return EPERM;
 	}
 
diff --git a/lib/syslib/safecopies.c b/lib/syslib/safecopies.c
index af46c3197..d9edea8fa 100644
--- a/lib/syslib/safecopies.c
+++ b/lib/syslib/safecopies.c
@@ -305,7 +305,7 @@ int access;
 	GID_CHECK(gid);
 	ACCESS_CHECK(access);
 
-	grants[gid].cp_flags = access | CPF_DIRECT | CPF_USED;
+	grants[gid].cp_flags = access | CPF_DIRECT | CPF_USED | CPF_VALID;
 	grants[gid].cp_u.cp_direct.cp_who_to = who;
 	grants[gid].cp_u.cp_direct.cp_start = addr;
 	grants[gid].cp_u.cp_direct.cp_len = bytes;
@@ -322,7 +322,7 @@ cp_grant_id_t his_gid;
 	GID_CHECK(gid);
 
 	/* Fill in new slot data. */
-	grants[gid].cp_flags = CPF_USED | CPF_INDIRECT;
+	grants[gid].cp_flags = CPF_USED | CPF_INDIRECT | CPF_VALID;
 	grants[gid].cp_u.cp_indirect.cp_who_to = who_to;
 	grants[gid].cp_u.cp_indirect.cp_who_from = who_from;
 	grants[gid].cp_u.cp_indirect.cp_grant = his_gid;
@@ -342,7 +342,7 @@ int access;
 	ACCESS_CHECK(access);
 
 	/* Fill in new slot data. */
-	grants[gid].cp_flags = CPF_USED | CPF_MAGIC | access;
+	grants[gid].cp_flags = CPF_USED | CPF_MAGIC | CPF_VALID | access;
 	grants[gid].cp_u.cp_magic.cp_who_to = who_to;
 	grants[gid].cp_u.cp_magic.cp_who_from = who_from;
 	grants[gid].cp_u.cp_magic.cp_start = addr;
@@ -351,3 +351,15 @@ int access;
 	return 0;
 }
 
+PUBLIC int
+cpf_setgrant_disable(gid)
+cp_grant_id_t gid;
+{
+	GID_CHECK(gid);
+
+	/* Grant is now no longer valid, but still in use. */
+	grants[gid].cp_flags = CPF_USED;
+
+	return 0;
+}
+