Re-implement non-preemptive section support.

Layered on top of the LITMUS control page.

2 files changed, 48 insertions, 62 deletions

diff --git a/src/kernel_iface.c b/src/kernel_iface.c
index 7cc676f..dbc4baa 100644
--- a/src/kernel_iface.c
+++ b/src/kernel_iface.c
@@ -1,76 +1,74 @@
+#include <sys/mman.h>
+#include <sys/fcntl.h> /* for O_RDWR */
+#include <sys/unistd.h>
+#include <sched.h> /* for sched_yield() */
+
+
 #include <stdio.h>
 
 #include "litmus.h"
 #include "internal.h"
 #include "asm.h"
 
-/* per real-time thread kernel <-> user space flags */
-
+#define LITMUS_CTRL_DEVICE "/dev/litmus/ctrl"
+#define CTRL_PAGES 1
 
-struct np_flag {
-        #define RT_PREEMPTIVE           0x2050 /* = NP */
-        #define RT_NON_PREEMPTIVE       0x4e50 /* =  P */
-        unsigned short preemptivity;
-
-        #define RT_EXIT_NP_REQUESTED    0x5251 /* = RQ */
-        unsigned short request;
-
-        unsigned int ctr;
-};
+static int map_file(const char* filename, void **addr, size_t size)
+{
+        int error = 0;
+        int fd;
 
-int register_np_flag(struct np_flag* flag);
-int signal_exit_np(void);
 
+        if (size > 0) {
+                fd = open(filename, O_RDWR);
+                if (fd >= 0) {
+                        *addr = mmap(NULL, size,
+                                     PROT_READ | PROT_WRITE,
+                                     MAP_PRIVATE,
+                                     fd, 0);
+                        if (*addr == MAP_FAILED)
+                                error = -1;
+                        close(fd);
+                } else
+                        error = fd;
+        } else
+                *addr = NULL;
+        return error;
+}
 
-#ifndef __sparc__
-static __thread struct np_flag np_flag;
-#endif
+/* thread-local pointer to control page */
+static __thread struct control_page *ctrl_page;
 
 int init_kernel_iface(void)
 {
-        int ret = 0;
-#ifdef FALSE
-#ifndef __sparc__ /* currently not supported in sparc64 */
-        np_flag.preemptivity = RT_PREEMPTIVE;
-        np_flag.ctr = 0;
-        ret = register_np_flag(&np_flag);
-        check("register_np_flag()");
-#endif
-#endif
-        return ret;
+        int err = 0;
+        long page_size = sysconf(_SC_PAGESIZE);
+
+        err = map_file(LITMUS_CTRL_DEVICE, (void**) &ctrl_page, CTRL_PAGES * page_size);
+        if (err) {
+                fprintf(stderr, "%s: cannot open LITMUS^RT control page (%m)\n",
+                        __FUNCTION__);
+        }
+
+        return err;
 }
 
 void enter_np(void)
 {
-#ifdef FALSE
-#ifndef __sparc__
-        if (++np_flag.ctr == 1)
-        {
-                np_flag.request = 0;
-                barrier();
-                np_flag.preemptivity = RT_NON_PREEMPTIVE;
-        }
-#else
-        fprintf(stderr, "enter_np: not implemented!\n");
-#endif
-#endif
+        if (likely(ctrl_page != NULL) || init_kernel_iface() == 0)
+                ctrl_page->np_flag++;
+        else
+                fprintf(stderr, "enter_np: control page not mapped!\n");
 }
 
 
 void exit_np(void)
 {
-#ifdef FALSE
-#ifndef __sparc__
-        if (--np_flag.ctr == 0)
-        {
-                np_flag.preemptivity = RT_PREEMPTIVE;
+        if (likely(ctrl_page != NULL) && --ctrl_page->np_flag == 0) {
+                /* became preemptive, let's check for delayed preemptions */
                 barrier();
-                if (np_flag.request == RT_EXIT_NP_REQUESTED)
-                        signal_exit_np();
+                if (ctrl_page->delayed_preemption)
+                        sched_yield();
         }
-#else
-        fprintf(stderr, "exit_np: not implemented!\n");
-#endif
-#endif
 }
 
diff --git a/src/syscalls.c b/src/syscalls.c
index 1df2ac3..77a6277 100644
--- a/src/syscalls.c
+++ b/src/syscalls.c
@@ -31,18 +31,6 @@ int sleep_next_period(void)
         return syscall(__NR_complete_job);
 }
 
-#ifdef false
-int register_np_flag(struct np_flag *flag)
-{
-        return syscall(__NR_register_np_flag, flag);
-}
-
-int signal_exit_np(void)
-{
-        return syscall(__NR_exit_np);
-}
-#endif
-
 int od_openx(int fd, obj_type_t type, int obj_id, void *config)
 {
         return syscall(__NR_od_open, fd, type, obj_id, config);