[fs][v9fs] Add an example test for VirtIO 9p filesystem

Add a simple test to validate the filesystem APIs that connect the LK
filesystem layer and the virtualIO 9p devices. The test does the same as
`app/tests/v9p_tests.c` to mount the littlekernel codebase folder as the
`/v9p` on the LK filesystem. Then it tries to read the `LICENSE` file
under the codebase and show the first 1024 bytes of the file.

For example:

```
starting internet servers
starting app shell
entering main console loop
] v9fs_tests
0x80017060: 2f 2a 0a 20 2a 20 43 6f 70 79 72 69 67 68 74 20 |/*. * Copyright
0x80017070: 28 63 29 20 32 30 30 38 2d 32 30 31 35 20 54 72 |(c) 2008-2015 Tr
0x80017080: 61 76 69 73 20 47 65 69 73 65 6c 62 72 65 63 68 |avis Geiselbrech
0x80017090: 74 0a 20 2a 0a 20 2a 20 50 65 72 6d 69 73 73 69 |t. *. * Permissi
0x800170a0: 6f 6e 20 69 73 20 68 65 72 65 62 79 20 67 72 61 |on is hereby gra
...
```

Signed-off-by: Cody Wong <codycswong@google.com>

app/tests/include/app/tests.h

@@ -20,6 +20,7 @@ int clock_tests(int argc, const console_cmd_args *argv);
 int printf_tests(int argc, const console_cmd_args *argv);
 int printf_tests_float(int argc, const console_cmd_args *argv);
 int v9p_tests(int argc, const console_cmd_args *argv);
+int v9fs_tests(int argc, const console_cmd_args *argv);
 
 #endif
 

app/tests/rules.mk

@@ -12,6 +12,7 @@ MODULE_SRCS := \
     $(LOCAL_DIR)/thread_tests.c \
     $(LOCAL_DIR)/port_tests.c \
     $(LOCAL_DIR)/v9p_tests.c \
+    $(LOCAL_DIR)/v9fs_tests.c \
 
 MODULE_FLOAT_SRCS := \
     $(LOCAL_DIR)/benchmarks.c \

app/tests/tests.c

@@ -23,4 +23,5 @@ STATIC_COMMAND("fibo", "threaded fibonacci", &fibo)
 STATIC_COMMAND("spinner", "create a spinning thread", &spinner)
 STATIC_COMMAND("cbuf_tests", "test lib/cbuf", &cbuf_tests)
 STATIC_COMMAND("v9p_tests", "test dev/virtio/9p", &v9p_tests)
+STATIC_COMMAND("v9fs_tests", "test lib/fs/9p", &v9fs_tests)
 STATIC_COMMAND_END(tests);

app/tests/v9fs_tests.c

@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2024 Cody Wong
+ *
+ * Use of this source code is governed by a MIT-style
+ * license that can be found in the LICENSE file or at
+ * https://opensource.org/licenses/MIT
+ */
+#include <app/tests.h>
+#include <lk/err.h>
+#include <lk/debug.h>
+
+#define _LOGF(fmt, args...) \
+    printf("[%s:%d] " fmt, __PRETTY_FUNCTION__, __LINE__, ##args)
+#define LOGF(x...) _LOGF(x)
+
+#if WITH_DEV_VIRTIO_9P
+#include <lib/fs.h>
+
+#define V9FS_MOUNT_POINT  "/v9p"
+#define V9FS_NAME         "9p"
+#define V9P_BDEV_NAME     "v9p0"
+
+#define BUF_SIZE          1024
+
+int v9fs_tests(int argc, const console_cmd_args *argv) {
+    status_t status;
+    ssize_t readbytes;
+    filehandle *handle;
+    char buf[BUF_SIZE];
+
+    status = fs_mount(V9FS_MOUNT_POINT, V9FS_NAME, V9P_BDEV_NAME);
+    if (status != NO_ERROR) {
+      LOGF("failed to mount v9p bdev (%s) onto mount point (%s): %d\n",
+           V9P_BDEV_NAME, V9FS_MOUNT_POINT, status);
+      return status;
+    }
+
+    status = fs_open_file(V9FS_MOUNT_POINT "/LICENSE", &handle);
+    if (status != NO_ERROR) {
+        LOGF("failed to open the target file: %d\n", status);
+        return status;
+    }
+
+    readbytes = fs_read_file(handle, buf, 0, BUF_SIZE);
+    if (readbytes < 0) {
+        LOGF("failed to read the target file: %ld\n", readbytes);
+        return status;
+    }
+
+    hexdump8(buf, BUF_SIZE);
+
+    status = fs_close_file(handle);
+    if (status != NO_ERROR) {
+        LOGF("failed to close the target file: %d\n", status);
+        return status;
+    }
+
+    status = fs_unmount(V9FS_MOUNT_POINT);
+    if (status != NO_ERROR) {
+      LOGF("failed to unmount v9p on mount point (%s): %d\n",
+           V9FS_MOUNT_POINT, status);
+      return status;
+    }
+
+    return NO_ERROR;
+}
+#else
+int v9fs_tests(int argc, const console_cmd_args *argv) {
+    LOGF("platform didn't have dev/virtio/9p supported\n");
+    return ERR_NOT_SUPPORTED;
+}
+#endif // WITH_DEV_VIRTIO_9P