3 files changed, 103 insertions, 11 deletions

diff --git a/kernel/include/comus/procs.h b/kernel/include/comus/procs.h
index 7b1a70a..717f27a 100644
--- a/kernel/include/comus/procs.h
+++ b/kernel/include/comus/procs.h
@@ -71,6 +71,11 @@ struct pcb {
 	uint64_t syscall;
 	uint64_t wakeup;
 	uint8_t exit_status;
+
+    // pipe to check for shared memory
+    void* shared_mem;
+    size_t shared_mem_pages;
+    pid_t shared_mem_source;
 };
 
 /// ordering of pcb queues
diff --git a/kernel/include/comus/syscalls.h b/kernel/include/comus/syscalls.h
index f714184..f27b879 100644
--- a/kernel/include/comus/syscalls.h
+++ b/kernel/include/comus/syscalls.h
@@ -30,9 +30,11 @@
 #define SYS_poweroff 17
 #define SYS_drm 18
 #define SYS_ticks 19
+#define SYS_allocshared 20
+#define SYS_popsharedmem 21
 
 // UPDATE THIS DEFINITION IF MORE SYSCALLS ARE ADDED!
-#define N_SYSCALLS 20
+#define N_SYSCALLS 22
 
 // interrupt vector entry for system calls
 #define VEC_SYSCALL 0x80
diff --git a/kernel/syscall.c b/kernel/syscall.c
index 96d2fcf..2b98ec1 100644
--- a/kernel/syscall.c
+++ b/kernel/syscall.c
@@ -324,17 +324,102 @@ static int sys_ticks(void)
 	return 0;
 }
 
+static int sys_popsharedmem(void)
+{
+	RET(void *, res_mem);
+	*res_mem = NULL;
+
+	if (pcb->shared_mem == NULL) {
+		return 1;
+	}
+
+	struct pcb *const sharer = pcb_find_pid(pcb->shared_mem_source);
+	if (sharer == NULL) {
+		// process died or something since sharing
+		pcb->shared_mem = NULL;
+		return 1;
+	}
+
+	void *result =
+		mem_mapaddr(pcb->memctx, mem_get_phys(sharer->memctx, pcb->shared_mem),
+					pcb->shared_mem, pcb->shared_mem_pages * PAGE_SIZE,
+					F_WRITEABLE | F_UNPRIVILEGED);
+
+	// if (!result) {
+	//  alert the other process that we cannot get its allocation?
+	// 	mem_free_pages(pcb->memctx, alloced);
+	// 	return 1;
+	// }
+
+	*res_mem = result;
+
+	pcb->shared_mem = NULL;
+
+	return 0;
+}
+
+static int sys_allocshared(void)
+{
+	ARG1(size_t, num_pages);
+	ARG2(unsigned short, otherpid); // same as pid_t
+	RET(void *, res_mem);
+	*res_mem = NULL;
+	assert(sizeof(unsigned short) == sizeof(pid_t),
+		   "out of date sys_memshare syscall, pid_t changed?");
+
+	if (otherpid == pcb->pid || otherpid == 0) {
+		return 1;
+	}
+
+	struct pcb *const otherpcb = pcb_find_pid(otherpid);
+	if (otherpcb == NULL) {
+		// no such target process exists
+		return 1;
+	}
+	if (otherpcb->shared_mem != NULL) {
+		// it has yet to consume the last allocshared given to it
+		return 1;
+	}
+
+	void *alloced =
+		mem_alloc_pages(pcb->memctx, num_pages, F_WRITEABLE | F_UNPRIVILEGED);
+
+	if (!alloced) {
+		return 1;
+	}
+
+	otherpcb->shared_mem = alloced;
+	otherpcb->shared_mem_source = pcb->pid;
+	otherpcb->shared_mem_pages = num_pages;
+
+	*res_mem = alloced;
+
+	return 0;
+}
+
 static int (*syscall_tbl[N_SYSCALLS])(void) = {
-	[SYS_exit] = sys_exit,		 [SYS_waitpid] = sys_waitpid,
-	[SYS_fork] = sys_fork,		 [SYS_exec] = NULL,
-	[SYS_open] = NULL,			 [SYS_close] = NULL,
-	[SYS_read] = NULL,			 [SYS_write] = sys_write,
-	[SYS_getpid] = sys_getpid,	 [SYS_getppid] = sys_getppid,
-	[SYS_gettime] = sys_gettime, [SYS_getprio] = sys_getprio,
-	[SYS_setprio] = sys_setprio, [SYS_kill] = sys_kill,
-	[SYS_sleep] = sys_sleep,	 [SYS_brk] = sys_brk,
-	[SYS_sbrk] = sys_sbrk,		 [SYS_poweroff] = sys_poweroff,
-	[SYS_drm] = sys_drm,		 [SYS_ticks] = sys_ticks,
+	[SYS_exit] = sys_exit,
+	[SYS_waitpid] = sys_waitpid,
+	[SYS_fork] = sys_fork,
+	[SYS_exec] = NULL,
+	[SYS_open] = NULL,
+	[SYS_close] = NULL,
+	[SYS_read] = NULL,
+	[SYS_write] = sys_write,
+	[SYS_getpid] = sys_getpid,
+	[SYS_getppid] = sys_getppid,
+	[SYS_gettime] = sys_gettime,
+	[SYS_getprio] = sys_getprio,
+	[SYS_setprio] = sys_setprio,
+	[SYS_kill] = sys_kill,
+	[SYS_sleep] = sys_sleep,
+	[SYS_brk] = sys_brk,
+	[SYS_sbrk] = sys_sbrk,
+	[SYS_poweroff] = sys_poweroff,
+	[SYS_drm] = sys_drm,
+	[SYS_ticks] = sys_ticks,
+	[SYS_allocshared] = sys_allocshared,
+	[SYS_popsharedmem] = sys_popsharedmem,
 };
 
 void syscall_handler(void)