[storage] Change GetDevicePath to return std::string

Avoid NUL terminator confusion by switching all GetDevicePath methods to
std::string.

Fixed: 63405
Change-Id: I3e58857d0bbe48f0ea2294968732a4bcc3ec2f81
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/580602
Reviewed-by: Brandon Castellano <bcastell@google.com>
Commit-Queue: Chris Suter <csuter@google.com>

Author: sutes-work

src/lib/storage/vfs/cpp/BUILD.gn

@@ -113,8 +113,10 @@ static_library("cpp") {
       "//zircon/public/lib/zx",
 
       # <fs/trace.h> has #include <lib/trace/event.h>.
-      "//zircon/public/lib/zxc",
       "//zircon/system/ulib/trace",
+
+      # <fs/vnode.h> has #include <lib/zx/status.h>
+      "//zircon/public/lib/zxc",
     ]
     deps += [
       "//sdk/fidl/fuchsia.cobalt:fuchsia.cobalt_c",

src/lib/storage/vfs/cpp/directory_connection.cc

@@ -487,10 +487,11 @@ void DirectoryConnection::GetDevicePath(GetDevicePathRequestView request,
     return;
   }
 
-  char name[fio::wire::kMaxPath];
-  size_t actual = 0;
-  zx_status_t status = vnode()->GetDevicePath(sizeof(name), name, &actual);
-  completer.Reply(status, fidl::StringView(name, actual));
+  if (auto device_path_or = vnode()->GetDevicePath(); device_path_or.is_error()) {
+    completer.Reply(device_path_or.error_value(), {});
+  } else {
+    completer.Reply(ZX_OK, fidl::StringView::FromExternal(device_path_or.value()));
+  }
 }
 
 void DirectoryConnection::AdvisoryLock(AdvisoryLockRequestView request,

src/lib/storage/vfs/cpp/vnode.cc

@@ -299,9 +299,7 @@ zx_status_t Vnode::GetVmo(int flags, zx::vmo* out_vmo, size_t* out_size) {
 
 zx_status_t Vnode::QueryFilesystem(fio::wire::FilesystemInfo* out) { return ZX_ERR_NOT_SUPPORTED; }
 
-zx_status_t Vnode::GetDevicePath(size_t buffer_len, char* out_name, size_t* out_len) {
-  return ZX_ERR_NOT_SUPPORTED;
-}
+zx::status<std::string> Vnode::GetDevicePath() const { return zx::error(ZX_ERR_NOT_SUPPORTED); }
 
 zx_status_t Vnode::AttachRemote(MountChannel h) { return ZX_ERR_NOT_SUPPORTED; }
 

src/lib/storage/vfs/cpp/vnode.h

@@ -37,6 +37,7 @@
 #include <fidl/fuchsia.io2/cpp/wire.h>
 #include <lib/file-lock/file-lock.h>
 #include <lib/zx/channel.h>
+#include <lib/zx/status.h>
 #include <lib/zx/stream.h>
 #include <zircon/device/vfs.h>
 
@@ -364,7 +365,7 @@ class Vnode : public VnodeRefCounted<Vnode>, public fbl::Recyclable<Vnode> {
   virtual zx_status_t QueryFilesystem(fuchsia_io::wire::FilesystemInfo* out);
 
   // Returns the name of the device backing the filesystem, if one exists.
-  virtual zx_status_t GetDevicePath(size_t buffer_len, char* out_name, size_t* out_len);
+  virtual zx::status<std::string> GetDevicePath() const;
 
   // Attaches a handle to the vnode, if possible. Otherwise, returns an error.
   virtual zx_status_t AttachRemote(MountChannel h);