Kernel+LibC+LibCore: Implement `renameat(2)`

Now with the ability to specify different bases for the old and new
paths.

Kernel/API/Syscall.h

@@ -418,7 +418,9 @@ struct SC_symlink_params {
 };
 
 struct SC_rename_params {
+    int olddirfd;
     StringArgument old_path;
+    int newdirfd;
     StringArgument new_path;
 };
 

Kernel/FileSystem/VirtualFileSystem.cpp

@@ -577,14 +577,14 @@ ErrorOr<void> VirtualFileSystem::chmod(Credentials const& credentials, StringVie
     return chmod(credentials, custody, mode);
 }
 
-ErrorOr<void> VirtualFileSystem::rename(Credentials const& credentials, StringView old_path, StringView new_path, Custody& base)
+ErrorOr<void> VirtualFileSystem::rename(Credentials const& credentials, Custody& old_base, StringView old_path, Custody& new_base, StringView new_path)
 {
     RefPtr<Custody> old_parent_custody;
-    auto old_custody = TRY(resolve_path(credentials, old_path, base, &old_parent_custody, O_NOFOLLOW_NOERROR));
+    auto old_custody = TRY(resolve_path(credentials, old_path, old_base, &old_parent_custody, O_NOFOLLOW_NOERROR));
     auto& old_inode = old_custody->inode();
 
     RefPtr<Custody> new_parent_custody;
-    auto new_custody_or_error = resolve_path(credentials, new_path, base, &new_parent_custody);
+    auto new_custody_or_error = resolve_path(credentials, new_path, new_base, &new_parent_custody);
     if (new_custody_or_error.is_error()) {
         if (new_custody_or_error.error().code() != ENOENT || !new_parent_custody)
             return new_custody_or_error.release_error();

Kernel/FileSystem/VirtualFileSystem.h

@@ -67,7 +67,7 @@ public:
     ErrorOr<InodeMetadata> lookup_metadata(Credentials const&, StringView path, Custody& base, int options = 0);
     ErrorOr<void> utime(Credentials const&, StringView path, Custody& base, time_t atime, time_t mtime);
     ErrorOr<void> utimensat(Credentials const&, StringView path, Custody& base, timespec const& atime, timespec const& mtime, int options = 0);
-    ErrorOr<void> rename(Credentials const&, StringView oldpath, StringView newpath, Custody& base);
+    ErrorOr<void> rename(Credentials const&, Custody& old_base, StringView oldpath, Custody& new_base, StringView newpath);
     ErrorOr<void> mknod(Credentials const&, StringView path, mode_t, dev_t, Custody& base);
     ErrorOr<NonnullRefPtr<Custody>> open_directory(Credentials const&, StringView path, Custody& base);
 

Kernel/Syscalls/rename.cpp

@@ -17,7 +17,7 @@ ErrorOr<FlatPtr> Process::sys$rename(Userspace<Syscall::SC_rename_params const*>
     auto params = TRY(copy_typed_from_user(user_params));
     auto old_path = TRY(get_syscall_path_argument(params.old_path));
     auto new_path = TRY(get_syscall_path_argument(params.new_path));
-    TRY(VirtualFileSystem::the().rename(credentials(), old_path->view(), new_path->view(), current_directory()));
+    TRY(VirtualFileSystem::the().rename(credentials(), TRY(custody_for_dirfd(params.olddirfd)), old_path->view(), TRY(custody_for_dirfd(params.newdirfd)), new_path->view()));
     return 0;
 }
 

Userland/Libraries/LibC/stdio.cpp

@@ -1125,12 +1125,18 @@ int fclose(FILE* stream)
 
 // https://pubs.opengroup.org/onlinepubs/9699919799/functions/rename.html
 int rename(char const* oldpath, char const* newpath)
+{
+    return renameat(AT_FDCWD, oldpath, AT_FDCWD, newpath);
+}
+
+// https://pubs.opengroup.org/onlinepubs/9699919799/functions/renameat.html
+int renameat(int olddirfd, char const* oldpath, int newdirfd, char const* newpath)
 {
     if (!oldpath || !newpath) {
         errno = EFAULT;
         return -1;
     }
-    Syscall::SC_rename_params params { { oldpath, strlen(oldpath) }, { newpath, strlen(newpath) } };
+    Syscall::SC_rename_params params { olddirfd, { oldpath, strlen(oldpath) }, newdirfd, { newpath, strlen(newpath) } };
     int rc = syscall(SC_rename, &params);
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }

Userland/Libraries/LibC/stdio.h

@@ -96,6 +96,7 @@ int setvbuf(FILE*, char* buf, int mode, size_t);
 void setbuf(FILE*, char* buf);
 void setlinebuf(FILE*);
 int rename(char const* oldpath, char const* newpath);
+int renameat(int olddirfd, char const* oldpath, int newdirfd, char const* newpath);
 FILE* tmpfile(void);
 char* tmpnam(char*);
 FILE* popen(char const* command, char const* type);

Userland/Libraries/LibCore/System.cpp

@@ -920,7 +920,9 @@ ErrorOr<void> rename(StringView old_path, StringView new_path)
 
 #ifdef AK_OS_SERENITY
     Syscall::SC_rename_params params {
+        .olddirfd = AT_FDCWD,
         .old_path = { old_path.characters_without_null_termination(), old_path.length() },
+        .newdirfd = AT_FDCWD,
         .new_path = { new_path.characters_without_null_termination(), new_path.length() },
     };
     int rc = syscall(SC_rename, &params);