Kernel: Make UserOrKernelBuffer R/W helpers return KResultOr<size_t>

This makes error propagation less cumbersome (and also exposed some
places where we were not doing it.)

15 files changed, 64 insertions, 85 deletions

diff --git a/Kernel/Console.cpp b/Kernel/Console.cpp
index 340c4d3fa8..d91d838425 100644
--- a/Kernel/Console.cpp
+++ b/Kernel/Console.cpp
@@ -57,14 +57,11 @@ Kernel::KResultOr<size_t> Console::write(FileDescription&, u64, const Kernel::Us
     if (!size)
         return 0;
 
-    ssize_t nread = data.read_buffered<256>(size, [&](const u8* bytes, size_t bytes_count) {
+    return data.read_buffered<256>(size, [&](u8 const* bytes, size_t bytes_count) {
         for (size_t i = 0; i < bytes_count; i++)
             put_char((char)bytes[i]);
-        return (ssize_t)bytes_count;
+        return bytes_count;
     });
-    if (nread < 0)
-        return Kernel::KResult((ErrnoCode)-nread);
-    return (size_t)nread;
 }
 
 void Console::put_char(char ch)
diff --git a/Kernel/Devices/AsyncDeviceRequest.h b/Kernel/Devices/AsyncDeviceRequest.h
index ab8ed3c626..b5c0035627 100644
--- a/Kernel/Devices/AsyncDeviceRequest.h
+++ b/Kernel/Devices/AsyncDeviceRequest.h
@@ -90,7 +90,7 @@ public:
     }
 
     template<size_t BUFFER_BYTES, typename... Args>
-    [[nodiscard]] bool write_to_buffer_buffered(UserOrKernelBuffer& buffer, Args... args)
+    [[nodiscard]] KResultOr<size_t> write_to_buffer_buffered(UserOrKernelBuffer& buffer, Args... args)
     {
         if (in_target_context(buffer))
             return buffer.write_buffered<BUFFER_BYTES>(forward<Args>(args)...);
@@ -108,7 +108,7 @@ public:
     }
 
     template<size_t BUFFER_BYTES, typename... Args>
-    [[nodiscard]] bool read_from_buffer_buffered(const UserOrKernelBuffer& buffer, Args... args)
+    [[nodiscard]] KResultOr<size_t> read_from_buffer_buffered(const UserOrKernelBuffer& buffer, Args... args)
     {
         if (in_target_context(buffer))
             return buffer.read_buffered<BUFFER_BYTES>(forward<Args>(args)...);
diff --git a/Kernel/Devices/HID/KeyboardDevice.cpp b/Kernel/Devices/HID/KeyboardDevice.cpp
index f9e87e4ea7..b49603cbf9 100644
--- a/Kernel/Devices/HID/KeyboardDevice.cpp
+++ b/Kernel/Devices/HID/KeyboardDevice.cpp
@@ -298,13 +298,13 @@ KResultOr<size_t> KeyboardDevice::read(FileDescription&, u64, UserOrKernelBuffer
 
         lock.unlock();
 
-        ssize_t n = buffer.write_buffered<sizeof(Event)>(sizeof(Event), [&](u8* data, size_t data_bytes) {
+        auto result = buffer.write_buffered<sizeof(Event)>(sizeof(Event), [&](u8* data, size_t data_bytes) {
             memcpy(data, &event, sizeof(Event));
-            return (ssize_t)data_bytes;
+            return data_bytes;
         });
-        if (n < 0)
-            return KResult((ErrnoCode)-n);
-        VERIFY((size_t)n == sizeof(Event));
+        if (result.is_error())
+            return result.error();
+        VERIFY(result.value() == sizeof(Event));
         nread += sizeof(Event);
 
         lock.lock();
diff --git a/Kernel/Devices/RandomDevice.cpp b/Kernel/Devices/RandomDevice.cpp
index 589ed1eeb3..6ada0a36d4 100644
--- a/Kernel/Devices/RandomDevice.cpp
+++ b/Kernel/Devices/RandomDevice.cpp
@@ -25,13 +25,10 @@ bool RandomDevice::can_read(const FileDescription&, size_t) const
 
 KResultOr<size_t> RandomDevice::read(FileDescription&, u64, UserOrKernelBuffer& buffer, size_t size)
 {
-    bool success = buffer.write_buffered<256>(size, [&](u8* data, size_t data_size) {
+    return buffer.write_buffered<256>(size, [&](u8* data, size_t data_size) {
         get_good_random_bytes(data, data_size);
-        return (ssize_t)data_size;
+        return data_size;
     });
-    if (!success)
-        return EFAULT;
-    return size;
 }
 
 KResultOr<size_t> RandomDevice::write(FileDescription&, u64, const UserOrKernelBuffer&, size_t size)
diff --git a/Kernel/Devices/SerialDevice.cpp b/Kernel/Devices/SerialDevice.cpp
index 263c684ffd..3be348172a 100644
--- a/Kernel/Devices/SerialDevice.cpp
+++ b/Kernel/Devices/SerialDevice.cpp
@@ -33,15 +33,11 @@ KResultOr<size_t> SerialDevice::read(FileDescription&, u64, UserOrKernelBuffer&
     if (!(get_line_status() & DataReady))
         return 0;
 
-    ssize_t nwritten = buffer.write_buffered<128>(size, [&](u8* data, size_t data_size) {
+    return buffer.write_buffered<128>(size, [&](u8* data, size_t data_size) {
         for (size_t i = 0; i < data_size; i++)
             data[i] = IO::in8(m_base_addr);
-        return (ssize_t)data_size;
+        return data_size;
     });
-    if (nwritten < 0)
-        return KResult((ErrnoCode)-nwritten);
-
-    return size;
 }
 
 bool SerialDevice::can_write(const FileDescription&, size_t) const
@@ -57,14 +53,11 @@ KResultOr<size_t> SerialDevice::write(FileDescription&, u64, const UserOrKernelB
     if (!(get_line_status() & EmptyTransmitterHoldingRegister))
         return 0;
 
-    ssize_t nread = buffer.read_buffered<128>(size, [&](const u8* data, size_t data_size) {
+    return buffer.read_buffered<128>(size, [&](u8 const* data, size_t data_size) {
         for (size_t i = 0; i < data_size; i++)
             IO::out8(m_base_addr, data[i]);
-        return (ssize_t)data_size;
+        return data_size;
     });
-    if (nread < 0)
-        return KResult((ErrnoCode)-nread);
-    return (size_t)nread;
 }
 
 String SerialDevice::device_name() const
diff --git a/Kernel/FileSystem/InodeWatcher.cpp b/Kernel/FileSystem/InodeWatcher.cpp
index fb7c36739a..29be55b502 100644
--- a/Kernel/FileSystem/InodeWatcher.cpp
+++ b/Kernel/FileSystem/InodeWatcher.cpp
@@ -48,7 +48,7 @@ KResultOr<size_t> InodeWatcher::read(FileDescription&, u64, UserOrKernelBuffer&
     if (buffer_size < bytes_to_write)
         return EINVAL;
 
-    ssize_t nwritten = buffer.write_buffered<MAXIMUM_EVENT_SIZE>(bytes_to_write, [&](u8* data, size_t data_bytes) {
+    auto result = buffer.write_buffered<MAXIMUM_EVENT_SIZE>(bytes_to_write, [&](u8* data, size_t data_bytes) {
         size_t offset = 0;
 
         memcpy(data + offset, &event.wd, sizeof(InodeWatcherEvent::watch_descriptor));
@@ -64,12 +64,10 @@ KResultOr<size_t> InodeWatcher::read(FileDescription&, u64, UserOrKernelBuffer&
             memset(data + offset, 0, sizeof(InodeWatcherEvent::name_length));
         }
 
-        return (ssize_t)data_bytes;
+        return data_bytes;
     });
-    if (nwritten < 0)
-        return KResult((ErrnoCode)-nwritten);
     evaluate_block_conditions();
-    return bytes_to_write;
+    return result;
 }
 
 KResult InodeWatcher::close()
diff --git a/Kernel/FileSystem/ProcFS.cpp b/Kernel/FileSystem/ProcFS.cpp
index 07789b904a..777bb5b936 100644
--- a/Kernel/FileSystem/ProcFS.cpp
+++ b/Kernel/FileSystem/ProcFS.cpp
@@ -903,17 +903,17 @@ static ssize_t write_sys_bool(InodeIdentifier inode_id, const UserOrKernelBuffer
 
     char value = 0;
     bool did_read = false;
-    ssize_t nread = buffer.read_buffered<1>(1, [&](const u8* data, size_t) {
+    auto result = buffer.read_buffered<1>(1, [&](u8 const* data, size_t) {
         if (did_read)
             return 0;
         value = (char)data[0];
         did_read = true;
         return 1;
     });
-    if (nread < 0)
-        return nread;
-    VERIFY(nread == 0 || (nread == 1 && did_read));
-    if (nread == 0 || !(value == '0' || value == '1'))
+    if (result.is_error())
+        return result.error();
+    VERIFY(result.value() == 0 || (result.value() == 1 && did_read));
+    if (result.value() == 0 || !(value == '0' || value == '1'))
         return (ssize_t)size;
 
     auto* lockable_bool = reinterpret_cast<Lockable<bool>*>(variable.address);
diff --git a/Kernel/Process.h b/Kernel/Process.h
index 94cbdccf27..7a8881e37e 100644
--- a/Kernel/Process.h
+++ b/Kernel/Process.h
@@ -255,7 +255,7 @@ public:
     KResultOr<int> sys$inode_watcher_add_watch(Userspace<const Syscall::SC_inode_watcher_add_watch_params*> user_params);
     KResultOr<int> sys$inode_watcher_remove_watch(int fd, int wd);
     KResultOr<int> sys$dbgputch(u8);
-    KResultOr<int> sys$dbgputstr(Userspace<const u8*>, int length);
+    KResultOr<size_t> sys$dbgputstr(Userspace<const u8*>, int length);
     KResultOr<int> sys$dump_backtrace();
     KResultOr<pid_t> sys$gettid();
     KResultOr<int> sys$donate(pid_t tid);
@@ -372,7 +372,7 @@ public:
     KResultOr<int> sys$halt();
     KResultOr<int> sys$reboot();
     KResultOr<int> sys$realpath(Userspace<const Syscall::SC_realpath_params*>);
-    KResultOr<ssize_t> sys$getrandom(Userspace<void*>, size_t, unsigned int);
+    KResultOr<size_t> sys$getrandom(Userspace<void*>, size_t, unsigned int);
     KResultOr<int> sys$getkeymap(Userspace<const Syscall::SC_getkeymap_params*>);
     KResultOr<int> sys$setkeymap(Userspace<const Syscall::SC_setkeymap_params*>);
     KResultOr<int> sys$module_load(Userspace<const char*> path, size_t path_length);
diff --git a/Kernel/Storage/IDEChannel.cpp b/Kernel/Storage/IDEChannel.cpp
index 91403b26ae..5b5a54da33 100644
--- a/Kernel/Storage/IDEChannel.cpp
+++ b/Kernel/Storage/IDEChannel.cpp
@@ -476,12 +476,12 @@ bool IDEChannel::ata_do_read_sector()
     dbgln_if(PATA_DEBUG, "IDEChannel::ata_do_read_sector");
     auto& request = *m_current_request;
     auto out_buffer = request.buffer().offset(m_current_request_block_index * 512);
-    ssize_t nwritten = request.write_to_buffer_buffered<512>(out_buffer, 512, [&](u8* buffer, size_t buffer_bytes) {
+    auto result = request.write_to_buffer_buffered<512>(out_buffer, 512, [&](u8* buffer, size_t buffer_bytes) {
         for (size_t i = 0; i < buffer_bytes; i += sizeof(u16))
             *(u16*)&buffer[i] = IO::in16(m_io_group.io_base().offset(ATA_REG_DATA).get());
-        return (ssize_t)buffer_bytes;
+        return buffer_bytes;
     });
-    if (nwritten < 0) {
+    if (result.is_error()) {
         // TODO: Do we need to abort the PATA read if this wasn't the last block?
         complete_current_request(AsyncDeviceRequest::MemoryFault);
         return false;
@@ -518,12 +518,12 @@ void IDEChannel::ata_do_write_sector()
 
     auto in_buffer = request.buffer().offset(m_current_request_block_index * 512);
     dbgln_if(PATA_DEBUG, "IDEChannel: Writing 512 bytes (part {}) (status={:#02x})...", m_current_request_block_index, status);
-    ssize_t nread = request.read_from_buffer_buffered<512>(in_buffer, 512, [&](const u8* buffer, size_t buffer_bytes) {
+    auto result = request.read_from_buffer_buffered<512>(in_buffer, 512, [&](u8 const* buffer, size_t buffer_bytes) {
         for (size_t i = 0; i < buffer_bytes; i += sizeof(u16))
             IO::out16(m_io_group.io_base().offset(ATA_REG_DATA).get(), *(const u16*)&buffer[i]);
-        return (ssize_t)buffer_bytes;
+        return buffer_bytes;
     });
-    if (nread < 0)
+    if (result.is_error())
         complete_current_request(AsyncDeviceRequest::MemoryFault);
 }
 
diff --git a/Kernel/Syscalls/debug.cpp b/Kernel/Syscalls/debug.cpp
index d02bb185e9..5d2ddf24a6 100644
--- a/Kernel/Syscalls/debug.cpp
+++ b/Kernel/Syscalls/debug.cpp
@@ -23,7 +23,7 @@ KResultOr<int> Process::sys$dbgputch(u8 ch)
     return 0;
 }
 
-KResultOr<int> Process::sys$dbgputstr(Userspace<const u8*> characters, int length)
+KResultOr<size_t> Process::sys$dbgputstr(Userspace<const u8*> characters, int length)
 {
     if (length <= 0)
         return 0;
@@ -31,14 +31,11 @@ KResultOr<int> Process::sys$dbgputstr(Userspace<const u8*> characters, int lengt
     auto buffer = UserOrKernelBuffer::for_user_buffer(characters, length);
     if (!buffer.has_value())
         return EFAULT;
-    ssize_t nread = buffer.value().read_buffered<1024>(length, [&](const u8* buffer, size_t buffer_size) {
+    return buffer.value().read_buffered<1024>(length, [&](u8 const* buffer, size_t buffer_size) {
         for (size_t i = 0; i < buffer_size; ++i)
             IO::out8(0xe9, buffer[i]);
-        return (ssize_t)buffer_size;
+        return buffer_size;
     });
-    if (nread < 0)
-        return (int)nread;
-    return 0;
 }
 
 }
diff --git a/Kernel/Syscalls/getrandom.cpp b/Kernel/Syscalls/getrandom.cpp
index a51c3aae35..8000b25ef2 100644
--- a/Kernel/Syscalls/getrandom.cpp
+++ b/Kernel/Syscalls/getrandom.cpp
@@ -13,7 +13,7 @@ namespace Kernel {
 // We don't use the flag yet, but we could use it for distinguishing
 // random source like Linux, unlike the OpenBSD equivalent. However, if we
 // do, we should be able of the caveats that Linux has dealt with.
-KResultOr<ssize_t> Process::sys$getrandom(Userspace<void*> buffer, size_t buffer_size, [[maybe_unused]] unsigned flags)
+KResultOr<size_t> Process::sys$getrandom(Userspace<void*> buffer, size_t buffer_size, [[maybe_unused]] unsigned flags)
 {
     REQUIRE_PROMISE(stdio);
     if (buffer_size <= 0)
@@ -22,11 +22,10 @@ KResultOr<ssize_t> Process::sys$getrandom(Userspace<void*> buffer, size_t buffer
     auto data_buffer = UserOrKernelBuffer::for_user_buffer(buffer, buffer_size);
     if (!data_buffer.has_value())
         return EFAULT;
-    ssize_t nwritten = data_buffer.value().write_buffered<1024>(buffer_size, [&](u8* buffer, size_t buffer_bytes) {
+    return data_buffer.value().write_buffered<1024>(buffer_size, [&](u8* buffer, size_t buffer_bytes) {
         get_good_random_bytes(buffer, buffer_bytes);
-        return (ssize_t)buffer_bytes;
+        return buffer_bytes;
     });
-    return nwritten;
 }
 
 }
diff --git a/Kernel/TTY/SlavePTY.cpp b/Kernel/TTY/SlavePTY.cpp
index a53a378846..65bcd89a85 100644
--- a/Kernel/TTY/SlavePTY.cpp
+++ b/Kernel/TTY/SlavePTY.cpp
@@ -46,12 +46,12 @@ void SlavePTY::echo(u8 ch)
 
 void SlavePTY::on_master_write(const UserOrKernelBuffer& buffer, ssize_t size)
 {
-    ssize_t nread = buffer.read_buffered<128>(size, [&](const u8* data, size_t data_size) {
+    auto result = buffer.read_buffered<128>(size, [&](u8 const* data, size_t data_size) {
         for (size_t i = 0; i < data_size; ++i)
             emit(data[i], false);
-        return (ssize_t)data_size;
+        return data_size;
     });
-    if (nread > 0)
+    if (!result.is_error())
         evaluate_block_conditions();
 }
 
diff --git a/Kernel/TTY/TTY.cpp b/Kernel/TTY/TTY.cpp
index 020150c86f..516b255e4d 100644
--- a/Kernel/TTY/TTY.cpp
+++ b/Kernel/TTY/TTY.cpp
@@ -43,10 +43,10 @@ KResultOr<size_t> TTY::read(FileDescription&, u64, UserOrKernelBuffer& buffer, s
     if (m_input_buffer.size() < static_cast<size_t>(size))
         size = m_input_buffer.size();
 
-    ssize_t nwritten;
+    KResultOr<size_t> result = 0;
     bool need_evaluate_block_conditions = false;
     if (in_canonical_mode()) {
-        nwritten = buffer.write_buffered<512>(size, [&](u8* data, size_t data_size) {
+        result = buffer.write_buffered<512>(size, [&](u8* data, size_t data_size) {
             size_t i = 0;
             for (; i < data_size; i++) {
                 u8 ch = m_input_buffer.dequeue();
@@ -64,10 +64,10 @@ KResultOr<size_t> TTY::read(FileDescription&, u64, UserOrKernelBuffer& buffer, s
                 }
                 data[i] = ch;
             }
-            return (ssize_t)i;
+            return i;
         });
     } else {
-        nwritten = buffer.write_buffered<512>(size, [&](u8* data, size_t data_size) {
+        result = buffer.write_buffered<512>(size, [&](u8* data, size_t data_size) {
             for (size_t i = 0; i < data_size; i++) {
                 auto ch = m_input_buffer.dequeue();
                 if (ch == '\r' && m_termios.c_iflag & ICRNL)
@@ -76,14 +76,12 @@ KResultOr<size_t> TTY::read(FileDescription&, u64, UserOrKernelBuffer& buffer, s
                     ch = '\r';
                 data[i] = ch;
             }
-            return (ssize_t)data_size;
+            return data_size;
         });
     }
-    if (nwritten < 0)
-        return KResult((ErrnoCode)-nwritten);
-    if (nwritten > 0 || need_evaluate_block_conditions)
+    if ((!result.is_error() && result.value() > 0) || need_evaluate_block_conditions)
         evaluate_block_conditions();
-    return (size_t)nwritten;
+    return result;
 }
 
 KResultOr<size_t> TTY::write(FileDescription&, u64, const UserOrKernelBuffer& buffer, size_t size)
@@ -93,8 +91,8 @@ KResultOr<size_t> TTY::write(FileDescription&, u64, const UserOrKernelBuffer& bu
         return EINTR;
     }
 
-    const size_t num_chars = 256;
-    ssize_t nread = buffer.read_buffered<num_chars>((size_t)size, [&](const u8* data, size_t buffer_bytes) {
+    constexpr size_t num_chars = 256;
+    return buffer.read_buffered<num_chars>(size, [&](u8 const* data, size_t buffer_bytes) {
         u8 modified_data[num_chars * 2];
         size_t extra_chars = 0;
         for (size_t i = 0; i < buffer_bytes; ++i) {
@@ -106,10 +104,8 @@ KResultOr<size_t> TTY::write(FileDescription&, u64, const UserOrKernelBuffer& bu
             modified_data[i + extra_chars] = ch;
         }
         on_tty_write(UserOrKernelBuffer::for_kernel_buffer(modified_data), buffer_bytes + extra_chars);
-        return (ssize_t)buffer_bytes;
+        return buffer_bytes;
     });
-
-    return nread;
 }
 
 bool TTY::can_read(const FileDescription&, size_t) const
diff --git a/Kernel/TTY/VirtualConsole.cpp b/Kernel/TTY/VirtualConsole.cpp
index e33fdbe7c0..5ac13edee4 100644
--- a/Kernel/TTY/VirtualConsole.cpp
+++ b/Kernel/TTY/VirtualConsole.cpp
@@ -226,14 +226,16 @@ void VirtualConsole::on_key_pressed(KeyEvent event)
 ssize_t VirtualConsole::on_tty_write(const UserOrKernelBuffer& data, ssize_t size)
 {
     ScopedSpinLock lock(s_lock);
-    ssize_t nread = data.read_buffered<512>((size_t)size, [&](const u8* buffer, size_t buffer_bytes) {
+    auto result = data.read_buffered<512>((size_t)size, [&](u8 const* buffer, size_t buffer_bytes) {
         for (size_t i = 0; i < buffer_bytes; ++i)
             m_terminal.on_input(buffer[i]);
-        return (ssize_t)buffer_bytes;
+        return buffer_bytes;
     });
     if (m_active)
         flush_dirty_lines();
-    return nread;
+    if (result.is_error())
+        return result.error();
+    return (ssize_t)result.value();
 }
 
 void VirtualConsole::set_vga_start_row(u16 row)
diff --git a/Kernel/UserOrKernelBuffer.h b/Kernel/UserOrKernelBuffer.h
index 01fb1e2e8e..b5e79480ed 100644
--- a/Kernel/UserOrKernelBuffer.h
+++ b/Kernel/UserOrKernelBuffer.h
@@ -82,10 +82,10 @@ public:
     }
 
     template<size_t BUFFER_BYTES, typename F>
-    [[nodiscard]] ssize_t write_buffered(size_t offset, size_t len, F f)
+    [[nodiscard]] KResultOr<size_t> write_buffered(size_t offset, size_t len, F f)
     {
         if (!m_buffer)
-            return -EFAULT;
+            return EFAULT;
         if (is_kernel_buffer()) {
             // We're transferring directly to a kernel buffer, bypass
             return f(m_buffer + offset, len);
@@ -102,24 +102,24 @@ public:
                 return copied;
             VERIFY((size_t)copied <= to_copy);
             if (!write(buffer, nwritten, (size_t)copied))
-                return -EFAULT;
+                return EFAULT;
             nwritten += (size_t)copied;
             if ((size_t)copied < to_copy)
                 break;
         }
-        return (ssize_t)nwritten;
+        return nwritten;
     }
     template<size_t BUFFER_BYTES, typename F>
-    [[nodiscard]] ssize_t write_buffered(size_t len, F f)
+    [[nodiscard]] KResultOr<size_t> write_buffered(size_t len, F f)
     {
         return write_buffered<BUFFER_BYTES, F>(0, len, f);
     }
 
     template<size_t BUFFER_BYTES, typename F>
-    [[nodiscard]] ssize_t read_buffered(size_t offset, size_t len, F f) const
+    [[nodiscard]] KResultOr<size_t> read_buffered(size_t offset, size_t len, F f) const
     {
         if (!m_buffer)
-            return -EFAULT;
+            return EFAULT;
         if (is_kernel_buffer()) {
             // We're transferring directly from a kernel buffer, bypass
             return f(m_buffer + offset, len);
@@ -132,7 +132,7 @@ public:
         while (nread < len) {
             auto to_copy = min(sizeof(buffer), len - nread);
             if (!read(buffer, nread, to_copy))
-                return -EFAULT;
+                return EFAULT;
             ssize_t copied = f(buffer, to_copy);
             if (copied < 0)
                 return copied;
@@ -144,7 +144,7 @@ public:
         return nread;
     }
     template<size_t BUFFER_BYTES, typename F>
-    [[nodiscard]] ssize_t read_buffered(size_t len, F f) const
+    [[nodiscard]] KResultOr<size_t> read_buffered(size_t len, F f) const
     {
         return read_buffered<BUFFER_BYTES, F>(0, len, f);
     }