From cfbe01ffbe981f48072b16e0fc6225a00138db6d Mon Sep 17 00:00:00 2001
From: Max Kellermann <mk@cm4all.com>
Date: Mon, 27 Nov 2023 18:18:23 +0100
Subject: [PATCH] io/Beneath: add OpenDirectoryBeneath()

---
 src/io/Beneath.cxx | 25 +++++++++++++++++++++++++
 src/io/Beneath.hxx |  6 ++++++
 2 files changed, 31 insertions(+)

diff --git a/src/io/Beneath.cxx b/src/io/Beneath.cxx
index 1e164f529..577c082b8 100644
--- a/src/io/Beneath.cxx
+++ b/src/io/Beneath.cxx
@@ -35,3 +35,28 @@ OpenReadOnlyBeneath(FileAt file)
 
 	return fd;
 }
+
+static constexpr struct open_how directory_beneath{
+	.flags = O_DIRECTORY|O_RDONLY|O_NOCTTY|O_CLOEXEC,
+	.resolve = RESOLVE_BENEATH|RESOLVE_NO_MAGICLINKS,
+};
+
+UniqueFileDescriptor
+TryOpenDirectoryBeneath(FileAt file) noexcept
+{
+	assert(file.directory.IsDefined());
+
+	int fd = openat2(file.directory.Get(), file.name,
+			 &directory_beneath, sizeof(directory_beneath));
+	return UniqueFileDescriptor{fd};
+}
+
+UniqueFileDescriptor
+OpenDirectoryBeneath(FileAt file)
+{
+	auto fd = TryOpenDirectoryBeneath(file);
+	if (!fd.IsDefined())
+		throw FmtErrno("Failed to open '{}'", file.name);
+
+	return fd;
+}
diff --git a/src/io/Beneath.hxx b/src/io/Beneath.hxx
index 09fcf3369..75c2a3676 100644
--- a/src/io/Beneath.hxx
+++ b/src/io/Beneath.hxx
@@ -11,3 +11,9 @@ TryOpenReadOnlyBeneath(FileAt file) noexcept;
 
 UniqueFileDescriptor
 OpenReadOnlyBeneath(FileAt file);
+
+UniqueFileDescriptor
+TryOpenDirectoryBeneath(FileAt file) noexcept;
+
+UniqueFileDescriptor
+OpenDirectoryBeneath(FileAt file);