vfs: advisory locking + flock syscall

kernel-src/sys/syscalls/flock.c

@@ -0,0 +1,74 @@
+#include <kernel/syscalls.h>
+#include <kernel/file.h>
+#include <kernel/vfs.h>
+
+syscallret_t syscall_flock(context_t *, int fd, int op_flag) {
+	syscallret_t ret = {
+		.ret = -1
+	};
+
+	int op = op_flag &= ~ADVLOCK_NON_BLOCKING;
+	switch (op) {
+		case ADVLOCK_UNLOCK:
+		case ADVLOCK_SHARED:
+		case ADVLOCK_EXCLUSIVE:
+			break;
+		default:
+			ret.errno = EINVAL;
+			return ret;
+	}
+
+	file_t *file = fd_get(fd);
+	if (file == NULL) {
+		ret.errno = EBADF;
+		return ret;
+	}
+
+	MUTEX_ACQUIRE(&file->mutex);
+
+	advlock_t *advlock = file->advlock;
+	if (advlock)
+		ADVLOCK_REF(advlock);
+
+	if (op == ADVLOCK_UNLOCK && advlock == NULL) {
+		// trying to unlock a lock which does not exist, just leave
+		ret.errno = 0;
+		ret.ret = 0;
+		goto leave;
+	}
+
+	if (op != ADVLOCK_UNLOCK && advlock == NULL) {
+		// locking and the lock does not exist yet, allocate it
+		advlock = advlock_allocate();
+		if (advlock == NULL) {
+			ret.errno = ENOMEM;
+			goto leave;
+		}
+
+		file->advlock = advlock;
+		advlock->refcount = 2;
+	}
+
+	vnode_t *vn = file->vnode;
+	VOP_HOLD(vn);
+
+	// release the file so that it can be closed etc in case we block
+	MUTEX_RELEASE(&file->mutex);
+	fd_release(file);
+
+	ret.errno = VOP_ADVLOCK(vn, op_flag, advlock);
+	ret.ret = ret.errno ? -1 : 0;
+
+	VOP_RELEASE(vn);
+	ADVLOCK_UNREF(advlock);
+
+	return ret;
+
+	leave:
+	if (advlock)
+		ADVLOCK_UNREF(advlock);
+	MUTEX_RELEASE(&file->mutex);
+	fd_release(file);
+
+	return ret;
+}