kernel/vfs: `/vga` node

1 files changed, 47 insertions, 1 deletions

diff --git a/src/kernel/vfs/root.c b/src/kernel/vfs/root.c
index f4bdcc2..9833330 100644
--- a/src/kernel/vfs/root.c
+++ b/src/kernel/vfs/root.c
@@ -8,6 +8,7 @@
 enum {
 	HANDLE_ROOT,
 	HANDLE_TTY,
+	HANDLE_VGA,
 };
 
 static bool exacteq(struct vfs_request *req, const char *str) {
@@ -16,17 +17,48 @@ static bool exacteq(struct vfs_request *req, const char *str) {
 	return req->input.len == len && !memcmp(req->input.buf_kern, str, len);
 }
 
+/* truncates the length */
+static void req_preprocess(struct vfs_request *req, int max_len) {
+	// max_len is signed because req->*.len are signed too
+	// potential place for VULNs to occur - arbitrary kernel reads etc
+	if (req->offset < 0) {
+		// TODO negative offsets
+		req->offset = 0;
+	}
+
+	if (req->offset >= max_len) {
+		req->input.len = 0;
+		req->output.len = 0;
+		req->offset = max_len;
+		return;
+	}
+
+	if (req->input.len  < 0) req->input.len  = 0;
+	if (req->output.len < 0) req->output.len = 0;
+
+	req->input.len  = min(req->input.len,  max_len - req->offset);
+	req->output.len = min(req->output.len, max_len - req->offset);
+
+	assert(req->input.len >= 0);
+	assert(req->output.len >= 0);
+
+	assert(req->input.len + req->offset <= max_len);
+	assert(req->input.len + req->offset <= max_len);
+}
+
 int vfs_root_handler(struct vfs_request *req) {
 	switch (req->type) {
 		case VFSOP_OPEN:
 			if (exacteq(req, "/"))    return HANDLE_ROOT;
 			if (exacteq(req, "/tty")) return HANDLE_TTY;
+			if (exacteq(req, "/vga")) return HANDLE_VGA;
 			return -1;
 
 		case VFSOP_READ:
 			switch (req->id) {
 				case HANDLE_ROOT: {
-					const char *src = "tty"; // TODO document directory read format
+					// TODO document directory read format
+					const char *src = "tty\0vga\0";
 					if (req->output.len < 0) return 0; // is this needed? TODO make that a size_t or something
 					int len = min((size_t) req->output.len, strlen(src) + 1);
 					virt_cpy_to(req->caller->pages, req->output.buf, src, len);
@@ -40,6 +72,13 @@ int vfs_root_handler(struct vfs_request *req) {
 						tty_read(iter.frag, iter.frag_len);
 					return iter.prior;
 				}
+				case HANDLE_VGA: {
+					char *vga = (void*)0xB8000;
+					req_preprocess(req, 80*25*2);
+					virt_cpy_to(req->caller->pages, req->output.buf,
+							vga + req->offset, req->output.len);
+					return req->output.len;
+				}
 				default: panic_invalid_state();
 			}
 
@@ -54,6 +93,13 @@ int vfs_root_handler(struct vfs_request *req) {
 						tty_write(iter.frag, iter.frag_len);
 					return iter.prior;
 				}
+				case HANDLE_VGA: {
+					void *vga = (void*)0xB8000;
+					req_preprocess(req, 80*25*2);
+					virt_cpy_from(req->caller->pages, vga + req->offset,
+							req->input.buf, req->input.len);
+					return req->input.len;
+				}
 				default: panic_invalid_state();
 			}