Kernel+LibC: Implement FIONREAD ioctl

FIONREAD gets the number of bytes availible to read from a file
descriptor without blocking. I only implemented it for regular files and
sockets

Kernel/DoubleBuffer.h

@@ -38,6 +38,10 @@ public:
     bool is_empty() const { return m_empty; }
 
     size_t space_for_writing() const { return m_space_for_writing; }
+    size_t immediately_readable() const
+    {
+        return (m_read_buffer->size - m_read_buffer_index) + m_write_buffer->size;
+    }
 
     void set_unblock_callback(Function<void()> callback)
     {

Kernel/FileSystem/InodeFile.cpp

@@ -64,8 +64,6 @@ KResultOr<size_t> InodeFile::write(FileDescription& description, u64 offset, con
 
 KResult InodeFile::ioctl(FileDescription& description, unsigned request, Userspace<void*> arg)
 {
-    (void)description;
-
     switch (request) {
     case FIBMAP: {
         if (!Process::current().is_superuser())
@@ -88,6 +86,13 @@ KResult InodeFile::ioctl(FileDescription& description, unsigned request, Userspa
 
         return KSuccess;
     }
+    case FIONREAD: {
+        int remaining_bytes = inode().size() - description.offset();
+        if (!copy_to_user(Userspace<int*>(arg), &remaining_bytes))
+            return EFAULT;
+
+        return KSuccess;
+    }
     default:
         return EINVAL;
     }

Kernel/Net/IPv4Socket.cpp

@@ -770,6 +770,14 @@ KResult IPv4Socket::ioctl(FileDescription&, unsigned request, Userspace<void*> a
     case SIOCSARP:
     case SIOCDARP:
         return ioctl_arp();
+
+    case FIONREAD: {
+        int readable = m_receive_buffer->immediately_readable();
+        if (!copy_to_user(Userspace<int*>(arg), &readable))
+            return EFAULT;
+
+        return KSuccess;
+    }
     }
 
     return EINVAL;

Kernel/Net/LocalSocket.cpp

@@ -16,6 +16,7 @@
 #include <Kernel/StdLib.h>
 #include <Kernel/UnixTypes.h>
 #include <LibC/errno_numbers.h>
+#include <LibC/sys/ioctl_numbers.h>
 
 namespace Kernel {
 
@@ -431,6 +432,21 @@ KResult LocalSocket::getsockopt(FileDescription& description, int level, int opt
     }
 }
 
+KResult LocalSocket::ioctl(FileDescription& description, unsigned request, Userspace<void*> arg)
+{
+    switch (request) {
+    case FIONREAD: {
+        int readable = receive_buffer_for(description)->immediately_readable();
+        if (!copy_to_user(Userspace<int*>(arg), &readable))
+            return EFAULT;
+
+        return KSuccess;
+    }
+    }
+
+    return ENOTTY;
+}
+
 KResult LocalSocket::chmod(FileDescription&, mode_t mode)
 {
     if (m_file)

Kernel/Net/LocalSocket.h

@@ -47,6 +47,7 @@ public:
     virtual KResultOr<size_t> sendto(FileDescription&, const UserOrKernelBuffer&, size_t, int, Userspace<const sockaddr*>, socklen_t) override;
     virtual KResultOr<size_t> recvfrom(FileDescription&, UserOrKernelBuffer&, size_t, int flags, Userspace<sockaddr*>, Userspace<socklen_t*>, Time&) override;
     virtual KResult getsockopt(FileDescription&, int level, int option, Userspace<void*>, Userspace<socklen_t*>) override;
+    virtual KResult ioctl(FileDescription&, unsigned request, Userspace<void*> arg) override;
     virtual KResult chown(FileDescription&, uid_t, gid_t) override;
     virtual KResult chmod(FileDescription&, mode_t) override;
 

Userland/Libraries/LibC/sys/ioctl.h

@@ -11,8 +11,6 @@
 
 __BEGIN_DECLS
 
-#define FIONREAD 0x541B
-
 int ioctl(int fd, unsigned request, ...);
 
 __END_DECLS

Userland/Libraries/LibC/sys/ioctl_numbers.h

@@ -83,6 +83,7 @@ enum IOCtlNumber {
     SIOCDARP,
     FIBMAP,
     FIONBIO,
+    FIONREAD,
     KCOV_SETBUFSIZE,
     KCOV_ENABLE,
     KCOV_DISABLE,
@@ -126,3 +127,4 @@ enum IOCtlNumber {
 #define SIOCDARP SIOCDARP
 #define FIBMAP FIBMAP
 #define FIONBIO FIONBIO
+#define FIONREAD FIONREAD