Add allocshared() and popsharedmem() syscalls

3 files changed, 146 insertions, 0 deletions

diff --git a/user/forkman.c b/user/forkman.c
new file mode 100644
index 0000000..fb5ae5f
--- /dev/null
+++ b/user/forkman.c
@@ -0,0 +1,121 @@
+/*
+ * FORKMAN: a platformer game with IPC
+ *
+ * This executable will fork. One process is responsible for writing to the
+ * screen and getting user input, the other is responsible for game logic.
+ *
+ */
+
+#include <unistd.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+#define GAME_WIDTH 480
+#define GAME_HEIGHT 360
+#define SHARED_PAGES 10
+#define PAGE_SIZE 4096
+
+typedef struct {
+	uint32_t *mapped_memory;
+	int width;
+	int height;
+	int bpp;
+	int scale;
+	size_t size;
+} framebuffer;
+
+typedef struct {
+	volatile size_t frame;
+	volatile size_t dummy_counter;
+	volatile int lock;
+	volatile uint8_t mem[PAGE_SIZE * (SHARED_PAGES - 1)];
+} sharedmem;
+
+static int display_server_entry(sharedmem *);
+static int client_entry(sharedmem *);
+
+int main(void)
+{
+	uint8_t *current_break = sbrk(0);
+	if (!current_break) {
+		fprintf(stderr, "sbrk failure\n");
+		return 1;
+	}
+
+	printf("ABOUT TO FORK\n");
+
+	int child = fork();
+	if (child < 0) {
+		fprintf(stderr, "fork failed!\n");
+		return 1;
+	}
+
+	if (child) {
+		printf("FORK GOOD, CHILD IS %d\n", child);
+		sharedmem *shared = allocshared(SHARED_PAGES, child);
+		if (!shared) {
+			fprintf(stderr, "memory share failure\n");
+			return 1;
+		}
+
+		return display_server_entry(shared);
+	} else {
+		printf("FORK GOOD, WE ARE CHILD\n");
+
+		sharedmem *shared;
+
+		while (!(shared = popsharedmem()))
+			sleep(1);
+
+		return client_entry(shared);
+	}
+}
+
+static void set_pixel(framebuffer *fb, size_t x, size_t y,
+					  int state) // state is 0 or 1
+{
+	fb->mapped_memory[x + y * fb->width] = state * (0x00010101);
+}
+
+static int display_server_entry(sharedmem *shared)
+{
+	framebuffer fb;
+	if (drm((void **)&fb.mapped_memory, &fb.width, &fb.height, &fb.bpp)) {
+		fprintf(stderr, "Unable to map framebuffer, display server failing\n");
+		return 1;
+	}
+
+	fb.size = (fb.width * fb.height * fb.bpp) / 8;
+
+	size_t last_frame = 1;
+
+	while (1) {
+		if (shared->frame == last_frame) {
+			continue;
+		}
+
+		printf("server writing frame %zu\n", last_frame);
+
+		last_frame += 1;
+		shared->frame = last_frame;
+	}
+
+	return 0;
+}
+
+static int client_entry(sharedmem *shared)
+{
+	size_t last_frame = shared->frame;
+	do {
+		if (last_frame == shared->frame)
+			continue;
+
+		printf("client writing frame %zu\n", last_frame);
+
+		last_frame += 1;
+		shared->frame = last_frame;
+	} while (1);
+
+	return 0;
+}
diff --git a/user/include/unistd.h b/user/include/unistd.h
index cad3a81..27b6d31 100644
--- a/user/include/unistd.h
+++ b/user/include/unistd.h
@@ -187,6 +187,29 @@ extern void *brk(const void *addr);
 extern void *sbrk(intptr_t increment);
 
 /**
+ * Allocate a number of pages shared with another PID. Does not map the pages
+ * into the other process's vtable until the other process calls popsharedmem().
+ *
+ * @param num_pages number of pages to allocate
+ * @param other_pid pid of other process
+ * @return pointer to the virtual address which will be accessible by both,
+ * after popsharedmem() is called.
+ */
+extern void* allocshared(size_t num_pages, int other_pid);
+
+/**
+ * Checks if another process has tried to share memory with us, and return it.
+ * No size information is returned, it is only guaranteed that there is at least
+ * one page in the shared allocation. To get around this, the sharer can write
+ * a size number to the start of the first page.
+ *
+ * @return page aligned pointer to the start of the shared pages, or NULL if no
+ * process has tried to share with us, or NULL if we the shared virtual address
+ * space is already occupied in the caller's pagetable.
+ */
+extern void* popsharedmem(void);
+
+/**
  * Poweroff the system.
  *
  * @return 1 on failure
diff --git a/user/lib/syscall.S b/user/lib/syscall.S
index 2ba4dc0..9e050bc 100644
--- a/user/lib/syscall.S
+++ b/user/lib/syscall.S
@@ -27,3 +27,5 @@ SYSCALL sbrk SYS_sbrk
 SYSCALL poweroff SYS_poweroff
 SYSCALL drm SYS_drm
 SYSCALL ticks SYS_ticks
+SYSCALL allocshared SYS_allocshared
+SYSCALL popsharedmem SYS_popsharedmem