kernel+libc: Add O_NONBLOCK

kernel/src/sys/file.cpp

@@ -21,7 +21,12 @@ Result<u64> sys_read(Registers*, SyscallArgs args)
 
     if (!descriptor.is_readable()) return err(EBADF);
 
-    while (descriptor.inode->blocking()) { kernel_sleep(10); }
+    while (descriptor.inode->blocking())
+    {
+        if (descriptor.should_block()) kernel_sleep(10);
+        else
+            return err(EAGAIN);
+    }
 
     usize nread = TRY(descriptor.inode->read(buf, descriptor.offset, size));
 

kernel/src/sys/open.cpp

@@ -7,7 +7,7 @@
 #include <bits/open-flags.h>
 
 // These flags are needed after open(), the rest only affect open().
-constexpr int FLAGS_TO_KEEP = O_RDWR | O_APPEND;
+constexpr int FLAGS_TO_KEEP = O_RDWR | O_APPEND | O_NONBLOCK;
 
 Result<u64> sys_open(Registers*, SyscallArgs args)
 {

kernel/src/thread/Thread.cpp

@@ -50,6 +50,11 @@ bool FileDescriptor::should_append()
     return flags & O_APPEND;
 }
 
+bool FileDescriptor::should_block()
+{
+    return flags & O_NONBLOCK;
+}
+
 bool FileDescriptor::is_readable()
 {
     return flags & O_RDONLY;

kernel/src/thread/Thread.h

@@ -29,6 +29,7 @@ struct FileDescriptor
     int flags { 0 };
 
     bool should_append();
+    bool should_block();
     bool is_writable();
     bool is_readable();
 };

libc/include/bits/open-flags.h

@@ -10,5 +10,6 @@
 #define O_CREAT 8
 #define O_EXCL 16
 #define O_TRUNC 32
+#define O_NONBLOCK 64
 
 #endif