Kernel: Make file description lookup return KResultOr

Instead of checking it at every call site (to generate EBADF), we make
file_description(fd) return a KResultOr<NonnullRefPtr<FileDescription>>.

This allows us to wrap all the calls in TRY(). :^)

The only place that got a little bit messier from this is sys$mount(),
and there's a whole bunch of things there in need of cleanup.

1 files changed, 1 insertions, 6 deletions

diff --git a/Kernel/Syscalls/chdir.cpp b/Kernel/Syscalls/chdir.cpp
index 5b5da7acfc..7b200e9f25 100644
--- a/Kernel/Syscalls/chdir.cpp
+++ b/Kernel/Syscalls/chdir.cpp
@@ -23,16 +23,11 @@ KResultOr<FlatPtr> Process::sys$fchdir(int fd)
 {
     VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this);
     REQUIRE_PROMISE(stdio);
-    auto description = fds().file_description(fd);
-    if (!description)
-        return EBADF;
-
+    auto description = TRY(fds().file_description(fd));
     if (!description->is_directory())
         return ENOTDIR;
-
     if (!description->metadata().may_execute(*this))
         return EACCES;
-
     m_cwd = description->custody();
     return 0;
 }