fdtable: read, write, close: only execute methods if non-NULL

Only invoke vtable methods read, write, and close if they are
non-NULL.

The close() vtable method is optional, so that should not return
an error if zvfs_close() is called and that method is
unimplemented.

Otherwise, if zvfs_read() or zvfs_write() are called and the
corresponding vtable method is unimplemented, fail setting
errno to EIO.

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>

lib/os/fdtable.c

@@ -301,7 +301,7 @@ int zvfs_alloc_fd(void *obj, const struct fd_op_vtable *vtable)
 	return fd;
 }
 
-ssize_t zvfs_read(int fd, void *buf, size_t sz)
+static ssize_t zvfs_rw(int fd, void *buf, size_t sz, bool is_write)
 {
 	ssize_t res;
 
@@ -310,63 +310,57 @@ ssize_t zvfs_read(int fd, void *buf, size_t sz)
 	}
 
 	(void)k_mutex_lock(&fdtable[fd].lock, K_FOREVER);
-	res = fdtable[fd].vtable->read_offs(fdtable[fd].obj, buf, sz, fdtable[fd].offset);
-	if (res > 0) {
-		switch (fdtable[fd].mode & ZVFS_MODE_IFMT) {
-		case ZVFS_MODE_IFDIR:
-		case ZVFS_MODE_IFBLK:
-		case ZVFS_MODE_IFSHM:
-		case ZVFS_MODE_IFREG:
-			fdtable[fd].offset += res;
-			break;
-		default:
-			break;
+
+	if (is_write) {
+		if (fdtable[fd].vtable->write_offset == NULL) {
+			res = -1;
+			errno = EIO;
+		} else {
+			res = fdtable[fd].vtable->write_offset(fdtable[fd].obj, buf, sz,
+							       fdtable[fd].offset);
 		}
+	} else {
+		if (fdtable[fd].vtable->read == NULL) {
+			res = -1;
+			errno = EIO;
+		} else {
+			res = fdtable[fd].vtable->read_offset(fdtable[fd].obj, buf, sz,
+							      fdtable[fd].offset);
+		}
+	}
+	if (res > 0) {
+		fdtable[fd].offset += res;
 	}
+
+unlock:
 	k_mutex_unlock(&fdtable[fd].lock);
 
 	return res;
 }
 
-ssize_t zvfs_write(int fd, const void *buf, size_t sz)
+ssize_t zvfs_read(int fd, void *buf, size_t sz)
 {
-	ssize_t res;
-
-	if (_check_fd(fd) < 0) {
-		return -1;
-	}
-
-	(void)k_mutex_lock(&fdtable[fd].lock, K_FOREVER);
-	res = fdtable[fd].vtable->write_offs(fdtable[fd].obj, buf, sz, fdtable[fd].offset);
-	if (res > 0) {
-		switch (fdtable[fd].mode & ZVFS_MODE_IFMT) {
-		case ZVFS_MODE_IFDIR:
-		case ZVFS_MODE_IFBLK:
-		case ZVFS_MODE_IFSHM:
-		case ZVFS_MODE_IFREG:
-			fdtable[fd].offset += res;
-			break;
-		default:
-			break;
-		}
-	}
-	k_mutex_unlock(&fdtable[fd].lock);
+	return zvfs_rw(fd, buf, sz, false);
+}
 
-	return res;
+ssize_t zvfs_write(int fd, const void *buf, size_t sz)
+{
+	return zvfs_rw(fd, (void *)buf, sz, true);
 }
 
 int zvfs_close(int fd)
 {
-	int res;
+	int res = 0;
 
 	if (_check_fd(fd) < 0) {
 		return -1;
 	}
 
 	(void)k_mutex_lock(&fdtable[fd].lock, K_FOREVER);
-
-	res = fdtable[fd].vtable->close(fdtable[fd].obj);
-
+	if (fdtable[fd].vtable->close != NULL) {
+		/* close() is optional - e.g. stdinout_fd_op_vtable */
+		res = fdtable[fd].vtable->close(fdtable[fd].obj);
+	}
 	k_mutex_unlock(&fdtable[fd].lock);
 
 	zvfs_free_fd(fd);