From 1ce32ef675aa576e4d99c9408539c32c5bbc40d5 Mon Sep 17 00:00:00 2001
From: Gunnar Beutner <gbeutner@serenityos.org>
Date: Thu, 27 May 2021 09:13:49 +0200
Subject: [PATCH] Kernel: Let the user read/write more than one page from/to
 dev files

Previously reads and writes to /dev/zero, /dev/full, /dev/null and
/dev/random were limited to 4096 bytes.

This removes that restriction so that users can enjoy more zero bytes
in their buffers.
---
 Kernel/Devices/FullDevice.cpp   | 5 ++---
 Kernel/Devices/NullDevice.cpp   | 2 +-
 Kernel/Devices/RandomDevice.cpp | 2 +-
 Kernel/Devices/ZeroDevice.cpp   | 7 +++----
 4 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/Kernel/Devices/FullDevice.cpp b/Kernel/Devices/FullDevice.cpp
index 318dec6486..6aab209181 100644
--- a/Kernel/Devices/FullDevice.cpp
+++ b/Kernel/Devices/FullDevice.cpp
@@ -28,10 +28,9 @@ bool FullDevice::can_read(const FileDescription&, size_t) const
 
 KResultOr<size_t> FullDevice::read(FileDescription&, u64, UserOrKernelBuffer& buffer, size_t size)
 {
-    ssize_t count = min(static_cast<size_t>(PAGE_SIZE), size);
-    if (!buffer.memset(0, count))
+    if (!buffer.memset(0, size))
         return EFAULT;
-    return count;
+    return size;
 }
 
 KResultOr<size_t> FullDevice::write(FileDescription&, u64, const UserOrKernelBuffer&, size_t size)
diff --git a/Kernel/Devices/NullDevice.cpp b/Kernel/Devices/NullDevice.cpp
index ace053aa51..9ceda5a96f 100644
--- a/Kernel/Devices/NullDevice.cpp
+++ b/Kernel/Devices/NullDevice.cpp
@@ -43,7 +43,7 @@ KResultOr<size_t> NullDevice::read(FileDescription&, u64, UserOrKernelBuffer&, s
 
 KResultOr<size_t> NullDevice::write(FileDescription&, u64, const UserOrKernelBuffer&, size_t buffer_size)
 {
-    return min(static_cast<size_t>(PAGE_SIZE), buffer_size);
+    return buffer_size;
 }
 
 }
diff --git a/Kernel/Devices/RandomDevice.cpp b/Kernel/Devices/RandomDevice.cpp
index 6ada0a36d4..1af96d818c 100644
--- a/Kernel/Devices/RandomDevice.cpp
+++ b/Kernel/Devices/RandomDevice.cpp
@@ -34,7 +34,7 @@ KResultOr<size_t> RandomDevice::read(FileDescription&, u64, UserOrKernelBuffer&
 KResultOr<size_t> RandomDevice::write(FileDescription&, u64, const UserOrKernelBuffer&, size_t size)
 {
     // FIXME: Use input for entropy? I guess that could be a neat feature?
-    return min(static_cast<size_t>(PAGE_SIZE), size);
+    return size;
 }
 
 }
diff --git a/Kernel/Devices/ZeroDevice.cpp b/Kernel/Devices/ZeroDevice.cpp
index 9bebece43f..1f3fddbf07 100644
--- a/Kernel/Devices/ZeroDevice.cpp
+++ b/Kernel/Devices/ZeroDevice.cpp
@@ -26,15 +26,14 @@ bool ZeroDevice::can_read(const FileDescription&, size_t) const
 
 KResultOr<size_t> ZeroDevice::read(FileDescription&, u64, UserOrKernelBuffer& buffer, size_t size)
 {
-    ssize_t count = min(static_cast<size_t>(PAGE_SIZE), size);
-    if (!buffer.memset(0, count))
+    if (!buffer.memset(0, size))
         return EFAULT;
-    return count;
+    return size;
 }
 
 KResultOr<size_t> ZeroDevice::write(FileDescription&, u64, const UserOrKernelBuffer&, size_t size)
 {
-    return min(static_cast<size_t>(PAGE_SIZE), size);
+    return size;
 }
 
 }