From 3666525d24f42bb35fca424ea9b3ce0528916945 Mon Sep 17 00:00:00 2001
From: Bananymous <oskari.alaranta@bananymous.com>
Date: Tue, 17 Sep 2024 16:38:15 +0300
Subject: [PATCH] Kernel/LibC: Implement `readlink` in terms of `readlinkat`

---
 kernel/include/kernel/Process.h               |  2 -
 kernel/kernel/Process.cpp                     | 41 ++++++++-----------
 .../libraries/LibC/include/sys/syscall.h      |  1 -
 userspace/libraries/LibC/unistd.cpp           |  3 +-
 4 files changed, 18 insertions(+), 29 deletions(-)

diff --git a/kernel/include/kernel/Process.h b/kernel/include/kernel/Process.h
index 82ad05e0..f7c98169 100644
--- a/kernel/include/kernel/Process.h
+++ b/kernel/include/kernel/Process.h
@@ -109,8 +109,6 @@ namespace Kernel
 		BAN::ErrorOr<long> sys_access(const char* path, int amode);
 		BAN::ErrorOr<long> sys_create_dir(const char*, mode_t);
 		BAN::ErrorOr<long> sys_unlink(const char*);
-		BAN::ErrorOr<long> readlink_impl(BAN::RefPtr<Inode>, char* buffer, size_t bufsize);
-		BAN::ErrorOr<long> sys_readlink(const char* path, char* buffer, size_t bufsize);
 		BAN::ErrorOr<long> sys_readlinkat(int fd, const char* path, char* buffer, size_t bufsize);
 
 		BAN::ErrorOr<long> sys_pread(int fd, void* buffer, size_t count, off_t offset);
diff --git a/kernel/kernel/Process.cpp b/kernel/kernel/Process.cpp
index 819a9e14..784cbbf1 100644
--- a/kernel/kernel/Process.cpp
+++ b/kernel/kernel/Process.cpp
@@ -994,37 +994,28 @@ namespace Kernel
 		return 0;
 	}
 
-	BAN::ErrorOr<long> Process::readlink_impl(BAN::RefPtr<Inode> inode, char* buffer, size_t bufsize)
-	{
-		// FIXME: no allocation needed
-		auto link_target = TRY(inode->link_target());
-
-		size_t byte_count = BAN::Math::min<size_t>(link_target.size(), bufsize);
-		memcpy(buffer, link_target.data(), byte_count);
-
-		return byte_count;
-	}
-
-	BAN::ErrorOr<long> Process::sys_readlink(const char* path, char* buffer, size_t bufsize)
-	{
-		LockGuard _(m_process_lock);
-		TRY(validate_string_access(path));
-		TRY(validate_pointer_access(buffer, bufsize, true));
-
-		auto absolute_path = TRY(absolute_path_of(path));
-		auto file = TRY(VirtualFileSystem::get().file_from_absolute_path(m_credentials, absolute_path, O_NOFOLLOW | O_RDONLY));
-		return readlink_impl(file.inode, buffer, bufsize);
-	}
-
 	BAN::ErrorOr<long> Process::sys_readlinkat(int fd, const char* path, char* buffer, size_t bufsize)
 	{
 		LockGuard _(m_process_lock);
 		TRY(validate_string_access(path));
 		TRY(validate_pointer_access(buffer, bufsize, true));
 
-		auto parent_file = TRY(m_open_file_descriptors.file_of(fd));
-		auto file = TRY(VirtualFileSystem::get().file_from_relative_path(parent_file, m_credentials, path, O_NOFOLLOW | O_RDONLY));
-		return readlink_impl(file.inode, buffer, bufsize);
+		VirtualFileSystem::File parent_file;
+		if (path[0] == '/')
+			parent_file = VirtualFileSystem::get().root_file();
+		else if (fd == AT_FDCWD)
+			parent_file = TRY(m_working_directory.clone());
+		else
+			parent_file = TRY(m_open_file_descriptors.file_of(fd));
+
+		auto inode = TRY(VirtualFileSystem::get().file_from_relative_path(parent_file, m_credentials, path, O_NOFOLLOW | O_RDONLY)).inode;
+
+		// FIXME: no allocation needed
+		auto link_target = TRY(inode->link_target());
+
+		const size_t byte_count = BAN::Math::min<size_t>(link_target.size(), bufsize);
+		memcpy(buffer, link_target.data(), byte_count);
+		return byte_count;
 	}
 
 	BAN::ErrorOr<long> Process::sys_pread(int fd, void* buffer, size_t count, off_t offset)
diff --git a/userspace/libraries/LibC/include/sys/syscall.h b/userspace/libraries/LibC/include/sys/syscall.h
index e4190818..071c70c7 100644
--- a/userspace/libraries/LibC/include/sys/syscall.h
+++ b/userspace/libraries/LibC/include/sys/syscall.h
@@ -55,7 +55,6 @@ __BEGIN_DECLS
 	O(SYS_FCHMOD,			fchmod)			\
 	O(SYS_CREATE_DIR,		create_dir)		\
 	O(SYS_UNLINK,			unlink) 		\
-	O(SYS_READLINK,			readlink)		\
 	O(SYS_READLINKAT,		readlinkat)		\
 	O(SYS_MSYNC,			msync)			\
 	O(SYS_PREAD,			pread)			\
diff --git a/userspace/libraries/LibC/unistd.cpp b/userspace/libraries/LibC/unistd.cpp
index 48639ce0..62493da1 100644
--- a/userspace/libraries/LibC/unistd.cpp
+++ b/userspace/libraries/LibC/unistd.cpp
@@ -3,6 +3,7 @@
 #include <kernel/Syscall.h>
 
 #include <errno.h>
+#include <fcntl.h>
 #include <pwd.h>
 #include <stdarg.h>
 #include <stdio.h>
@@ -86,7 +87,7 @@ ssize_t write(int fildes, const void* buf, size_t nbyte)
 
 ssize_t readlink(const char* __restrict path, char* __restrict buf, size_t bufsize)
 {
-	return syscall(SYS_READLINK, path, buf, bufsize);
+	return readlinkat(AT_FDCWD, path, buf, bufsize);
 }
 
 ssize_t readlinkat(int fd, const char* __restrict path, char* __restrict buf, size_t bufsize)