[PATCH RFC v3 31/90] cells: reserve the "spawn" slot

[Josef Bacik]

A task of a cell can neither create a cell nor start a task in one. So far
that looks like a side effect of the fact that no cellfd ever gets into a
cell. Make it an explicit rule that does not depend on that.

The rule fits the model: a cell can do what its slots hold, and the right
to spawn is a slot like any other. cell_may_spawn() checks it where a cell
is created and where a task is started in one.

There is nothing to put into the slot yet, so it is always empty for a
cell, and a task that is in no cell may always spawn. This patch only
reserves the name. Nested cells can later be enabled by filling the slot.

Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
---
 kernel/cell/slots.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/cell/slots.c b/kernel/cell/slots.c
index cc732c4e09f9..6ce8892f7908 100644
--- a/kernel/cell/slots.c
+++ b/kernel/cell/slots.c
@@ -165,6 +165,9 @@ SYSCALL_DEFINE5(cell_configure, int, cfd, unsigned int, cmd,
 		if (IS_ERR(key))
 			return PTR_ERR(no_free_ptr(key));
 	}
+	/* Reserved. See cell_may_spawn(). */
+	if (key && !strcmp(key, "spawn"))
+		return -EOPNOTSUPP;
 	if (cmd == CELL_SET_STRING) {
 		str = strndup_user(uvalue, 256);
 		if (IS_ERR(str))

-- 
2.55.0