add some scaffolding for file descriptors

7 files changed, 80 insertions, 0 deletions

diff --git a/src/init/syscalls.c b/src/init/syscalls.c
index 0be7917..4f207db 100644
--- a/src/init/syscalls.c
+++ b/src/init/syscalls.c
@@ -24,6 +24,18 @@ int _syscall_mount(const char *path, int len, fd_t fd) {
 	return _syscall(_SYSCALL_MOUNT, (int)path, len, fd);
 }
 
+int _syscall_fd_read(fd_t fd, char *buf, int len) {
+	return _syscall(_SYSCALL_FD_READ, fd, (int)buf, len);
+}
+
+int _syscall_fd_write(fd_t fd, char *buf, int len) {
+	return _syscall(_SYSCALL_FD_WRITE, fd, (int)buf, len);
+}
+
+int _syscall_fd_close(fd_t fd) {
+	return _syscall(_SYSCALL_FD_CLOSE, fd, 0, 0);
+}
+
 int _syscall_debuglog(const char *msg, size_t len) {
 	return _syscall(_SYSCALL_DEBUGLOG, (int)msg, len, 0);
 }
diff --git a/src/kernel/fd.c b/src/kernel/fd.c
new file mode 100644
index 0000000..54f1c72
--- /dev/null
+++ b/src/kernel/fd.c
@@ -0,0 +1,13 @@
+#include <kernel/fd.h>
+#include <kernel/panic.h>
+#include <kernel/proc.h>
+
+int fdop_dispatch(enum fdop fdop, fd_t fd, void *ptr, size_t len) {
+	if (fd < 0 || fd >= FD_MAX) return -1;
+	switch(process_current->fds[fd].type) {
+		case FD_EMPTY:
+			return -1;
+		default:
+			panic();
+	}
+}
diff --git a/src/kernel/fd.h b/src/kernel/fd.h
new file mode 100644
index 0000000..4976c7d
--- /dev/null
+++ b/src/kernel/fd.h
@@ -0,0 +1,23 @@
+#pragma once
+#include <stddef.h>
+
+#define FD_MAX 16
+
+typedef int fd_t; // TODO duplicated in syscalls.h
+
+enum fd_type {
+	FD_EMPTY,
+};
+
+struct fd {
+	enum fd_type type;
+};
+
+
+enum fdop { // describes the operations which can be done on file descriptors
+	FDOP_READ,
+	FDOP_WRITE,
+	FDOP_CLOSE,
+};
+
+int fdop_dispatch(enum fdop fdop, fd_t fd, void *ptr, size_t len);
diff --git a/src/kernel/proc.c b/src/kernel/proc.c
index f826d8a..4c278e6 100644
--- a/src/kernel/proc.c
+++ b/src/kernel/proc.c
@@ -21,6 +21,9 @@ struct process *process_seed() {
 
 	process_first = proc;
 
+	for (int i = 0; i < FD_MAX; i++)
+		proc->fds[i].type = FD_EMPTY;
+
 	// map the stack to the last page in memory
 	pagedir_map(proc->pages, (void*)~PAGE_MASK, page_alloc(1), true, true);
 	proc->stack_top = (void*) (proc->regs.esp = ~0xF);
diff --git a/src/kernel/proc.h b/src/kernel/proc.h
index ffc342a..0a1a42c 100644
--- a/src/kernel/proc.h
+++ b/src/kernel/proc.h
@@ -1,5 +1,6 @@
 #pragma once
 #include <kernel/arch/generic.h>
+#include <kernel/fd.h>
 #include <kernel/vfs/mount.h>
 
 enum process_state {
@@ -28,6 +29,8 @@ struct process {
 	size_t saved_len;
 
 	struct vfs_mount *mount;
+
+	struct fd fds[FD_MAX];
 };
 
 extern struct process *process_first;
diff --git a/src/kernel/syscalls.c b/src/kernel/syscalls.c
index 8ee90eb..4da5261 100644
--- a/src/kernel/syscalls.c
+++ b/src/kernel/syscalls.c
@@ -130,6 +130,18 @@ fail:
 	return -1;
 }
 
+int _syscall_fd_read(fd_t fd, char *buf, int len) {
+	return fdop_dispatch(FDOP_READ, fd, buf, len);
+}
+
+int _syscall_fd_write(fd_t fd, char *buf, int len) {
+	return fdop_dispatch(FDOP_WRITE, fd, buf, len);
+}
+
+int _syscall_fd_close(fd_t fd) {
+	return fdop_dispatch(FDOP_CLOSE, fd, 0, 0);
+}
+
 int _syscall_debuglog(const char *msg, size_t len) {
 	struct virt_iter iter;
 	virt_iter_new(&iter, (void*)msg, len, process_current->pages, true, false);
@@ -150,6 +162,12 @@ int syscall_handler(int num, int a, int b, int c) {
 			return _syscall_fs_open((void*)a, b);
 		case _SYSCALL_MOUNT:
 			return _syscall_mount((void*)a, b, c);
+		case _SYSCALL_FD_READ:
+			return _syscall_fd_read(a, (void*)b, c);
+		case _SYSCALL_FD_WRITE:
+			return _syscall_fd_write(a, (void*)b, c);
+		case _SYSCALL_FD_CLOSE:
+			return _syscall_fd_close(a);
 		case _SYSCALL_DEBUGLOG:
 			return _syscall_debuglog((void*)a, b);
 		default:
diff --git a/src/kernel/syscalls.h b/src/kernel/syscalls.h
index f3e8dc0..d8ca5c3 100644
--- a/src/kernel/syscalls.h
+++ b/src/kernel/syscalls.h
@@ -14,6 +14,10 @@ enum {
 	_SYSCALL_FS_OPEN,
 	_SYSCALL_MOUNT,
 
+	_SYSCALL_FD_READ,
+	_SYSCALL_FD_WRITE,
+	_SYSCALL_FD_CLOSE,
+
 	_SYSCALL_DEBUGLOG
 };
 
@@ -36,6 +40,10 @@ int _syscall_fork();
 fd_t _syscall_fs_open(const char *path, int len);
 int _syscall_mount(const char *path, int len, fd_t fd);
 
+int _syscall_fd_read(fd_t fd, char *buf, int len);
+int _syscall_fd_write(fd_t fd, char *buf, int len);
+int _syscall_fd_close(fd_t fd);
+
 /** Prints a message to the debug console.
  * @return the amount of bytes written (can be less than len)
  */