From acd8c8dba4537277044a7e5a5574c58548467d8e Mon Sep 17 00:00:00 2001
From: Tim Schumacher <timschumi@gmx.de>
Date: Sun, 16 Apr 2023 18:48:38 +0200
Subject: [PATCH] Kernel: Add `Inode::read_until_filled_or_end`

The existing `read_entire` is quite slow due to allocating and copying
multiple times, but it is simultaneously quite hard to get rid of in a
single step. As a replacement, add a new function that reads as much as
possible directly into a user-provided buffer.
---
 Kernel/FileSystem/Inode.cpp | 15 +++++++++++++++
 Kernel/FileSystem/Inode.h   |  1 +
 2 files changed, 16 insertions(+)

diff --git a/Kernel/FileSystem/Inode.cpp b/Kernel/FileSystem/Inode.cpp
index afe3959725..ec60311822 100644
--- a/Kernel/FileSystem/Inode.cpp
+++ b/Kernel/FileSystem/Inode.cpp
@@ -118,6 +118,21 @@ ErrorOr<size_t> Inode::read_bytes(off_t offset, size_t length, UserOrKernelBuffe
     return read_bytes_locked(offset, length, buffer, open_description);
 }
 
+ErrorOr<size_t> Inode::read_until_filled_or_end(off_t offset, size_t length, UserOrKernelBuffer buffer, OpenFileDescription* open_description) const
+{
+    auto remaining_length = length;
+
+    while (remaining_length > 0) {
+        auto filled_bytes = TRY(read_bytes(offset, remaining_length, buffer, open_description));
+        if (filled_bytes == 0)
+            break;
+        offset += filled_bytes;
+        remaining_length -= filled_bytes;
+    }
+
+    return length - remaining_length;
+}
+
 ErrorOr<void> Inode::update_timestamps([[maybe_unused]] Optional<Time> atime, [[maybe_unused]] Optional<Time> ctime, [[maybe_unused]] Optional<Time> mtime)
 {
     return ENOTIMPL;
diff --git a/Kernel/FileSystem/Inode.h b/Kernel/FileSystem/Inode.h
index b4cea6b440..c7fba48caa 100644
--- a/Kernel/FileSystem/Inode.h
+++ b/Kernel/FileSystem/Inode.h
@@ -57,6 +57,7 @@ public:
 
     ErrorOr<size_t> write_bytes(off_t, size_t, UserOrKernelBuffer const& data, OpenFileDescription*);
     ErrorOr<size_t> read_bytes(off_t, size_t, UserOrKernelBuffer& buffer, OpenFileDescription*) const;
+    ErrorOr<size_t> read_until_filled_or_end(off_t, size_t, UserOrKernelBuffer buffer, OpenFileDescription*) const;
 
     virtual ErrorOr<void> attach(OpenFileDescription&) { return {}; }
     virtual void detach(OpenFileDescription&) { }