5 files changed, 75 insertions, 3 deletions

diff --git a/src/cmd/tests/kernel/miscsyscall.c b/src/cmd/tests/kernel/miscsyscall.c
index 1317720..883fcee 100644
--- a/src/cmd/tests/kernel/miscsyscall.c
+++ b/src/cmd/tests/kernel/miscsyscall.c
@@ -326,6 +326,40 @@ static void test_getnull(void) {
 	close(h2);
 }
 
+static void test_dup_ro(void) {
+	char buf[2];
+
+	/* runs two times, trying to close either the original handle or the dup'd
+	 * one. */
+	for (int i = 0; i < 2; i++) {
+		hid_t h = _sys_open(TMPFILEPATH, strlen(TMPFILEPATH), OPEN_CREATE | OPEN_RW);
+		test(0 <= h);
+		hid_t h2 = _sys_dup(h, 0, DUP_SEARCH | DUP_RDONLY);
+		test(0 <= h2);
+
+		test(_sys_write(h, "hi", 2, 0, 0) == 2);
+		test(_sys_write(h2, "no", 2, 0, 0) == -EACCES);
+
+		test(_sys_read(h, buf, 2, 0) == 2);
+		test(memcmp(buf, "hi", 2) == 0);
+		test(_sys_read(h2, buf, 2, 0) == 2);
+		test(memcmp(buf, "hi", 2) == 0);
+
+		if (i == 0) {
+			_sys_close(h);
+			test(_sys_read(h2, buf, 2, 0) == 2);
+			test(memcmp(buf, "hi", 2) == 0);
+			_sys_close(h2);
+		} else {
+			_sys_close(h2);
+			test(_sys_write(h, "ay", 2, 0, 0) == 2);
+			test(_sys_read(h, buf, 2, 0) == 2);
+			test(memcmp(buf, "ay", 2) == 0);
+			_sys_close(h);
+		}
+	}
+}
+
 void r_k_miscsyscall(void) {
 	run_test(test_await);
 	run_test(test_await2);
@@ -338,4 +372,5 @@ void r_k_miscsyscall(void) {
 	run_test(test_badopen);
 	run_test(test_timer);
 	run_test(test_getnull);
+	run_test(test_dup_ro);
 }
diff --git a/src/kernel/handle.c b/src/kernel/handle.c
index ca4c4c4..882a4fa 100644
--- a/src/kernel/handle.c
+++ b/src/kernel/handle.c
@@ -19,12 +19,16 @@ void handle_close(Handle *h) {
 	if (--(h->refcount) > 0) return;
 
 	if (h->type == HANDLE_FILE) {
-		vfsreq_create((VfsReq) {
+		if (h->base) {
+			handle_close(h->base);
+		} else {
+			vfsreq_create((VfsReq) {
 				.type = VFSOP_CLOSE,
 				.id = h->file_id,
 				.caller = NULL,
 				.backend = h->backend,
 			});
+		}
 	} else if (h->type == HANDLE_PIPE) {
 		assert(!h->pipe.queued);
 		if (h->pipe.sister) {
diff --git a/src/kernel/handle.h b/src/kernel/handle.h
index d502d5d..af9d45a 100644
--- a/src/kernel/handle.h
+++ b/src/kernel/handle.h
@@ -13,16 +13,19 @@ enum handle_type {
 	HANDLE_NULL,
 };
 
+// TODO use unions
+// when making changes, keep in mind that dup creates copies of HANDLE_FILEs
 struct Handle {
 	enum handle_type type;
-	VfsBackend *backend; // HANDLE_FILE | HANDLE_FS_FRONT
-	void __user *file_id; // only applicable to HANDLE_FILE
+	VfsBackend *backend; /* HANDLE_FILE | HANDLE_FS_FRONT */
+	void __user *file_id; /* only applicable to HANDLE_FILE */
 	bool readable, writeable; /* HANDLE_FILE | HANDLE_PIPE */
 	VfsReq *req; /* HANDLE_FS_REQ */
 	struct {
 		Proc *queued;
 		Handle *sister; // the other end, not included in refcount
 	} pipe;
+	Handle *base; /* used by dup'd HANDLE_FILEs. */
 
 	size_t refcount;
 };
diff --git a/src/kernel/handleset.c b/src/kernel/handleset.c
index a25f5c7..fc2d426 100644
--- a/src/kernel/handleset.c
+++ b/src/kernel/handleset.c
@@ -89,6 +89,34 @@ hs_dup(HandleSet *hs, hid_t from, hid_t to, int flags)
 	fromh = hs_get(hs, from);
 
 	if (*toh) handle_close(*toh);
+
+	if (flags & (DUP_RDONLY | DUP_WRONLY)) {
+		if (!fromh || fromh->type != HANDLE_FILE) {
+			/* only errors out after closing the old handle */
+			*toh = NULL;
+			return -ENOSYS;
+		}
+
+		/* figure out if we need a need handle */
+		bool different = false;
+		different = different || ((flags & DUP_RDONLY) && fromh->writeable);
+		different = different || ((flags & DUP_WRONLY) && fromh->readable);
+
+		if (different) {
+			Handle *new = handle_init(HANDLE_FILE);
+			new->backend = fromh->backend;
+			if (new->backend) new->backend->usehcnt++;
+			new->file_id = fromh->file_id;
+			new->readable  = fromh->readable  && !(flags & DUP_WRONLY);
+			new->writeable = fromh->writeable && !(flags & DUP_RDONLY);
+			new->base = fromh;
+			fromh->refcount++;
+
+			*toh = new;
+			return to;
+		}
+	}
+
 	*toh = fromh;
 	if (fromh) fromh->refcount++;
 
diff --git a/src/libk/include/camellia/flags.h b/src/libk/include/camellia/flags.h
index a708f73..472215b 100644
--- a/src/libk/include/camellia/flags.h
+++ b/src/libk/include/camellia/flags.h
@@ -13,6 +13,8 @@
 #define FSR_DELEGATE 1
 
 #define DUP_SEARCH 1
+#define DUP_RDONLY 2
+#define DUP_WRONLY 4
 
 #define OPEN_READ 1
 #define OPEN_WRITE 2