MINOR: fd: add two flags ERR and SHUT to describe FD states
There's currently a big ambiguity on our use of POLLHUP because we
currently map POLLHUP and POLLRDHUP to FD_POLL_HUP. The first one
indicates a close in *both* directions while the second one indicates
a unidirectional close. Since we don't know from the resulting flag
we always have to read when reported. Furthermore kqueue only reports
unidirectional responses which are mapped to FD_POLL_HUP as well, and
their write closes are mapped to a general error.
We could add a new FD_POLL_RDHUP flag to improve the mapping, or
switch only to the POLL* flags, but that further complicates the
portability for operating systems like FreeBSD which do not have
POLLRDHUP but have its semantics.
Let's instead directly use the per-direction flag values we already
have, and it will be a first step in the direction of finer states.
Thus we introduce an ERR and a SHUT status for each direction, that
the pollers will be able to compute and pass to fd_update_events().
It's worth noting that FD_EV_STATUS already sees the two new flags,
but they are harmless since used only by fd_{recv,send}_state() which
are never called. Thus in its current state this patch must be totally
transparent.
diff --git a/include/types/fd.h b/include/types/fd.h
index 28f0c52..580e180 100644
--- a/include/types/fd.h
+++ b/include/types/fd.h
@@ -50,15 +50,21 @@
/* FD bits used for different polling states in each direction */
#define FD_EV_ACTIVE 1U
#define FD_EV_READY 2U
+#define FD_EV_SHUT 4U
+#define FD_EV_ERR 8U
/* bits positions for a few flags */
#define FD_EV_ACTIVE_R_BIT 0
-#define FD_EV_READY_R_BIT 1
+#define FD_EV_READY_R_BIT 1
+#define FD_EV_SHUT_R_BIT 2
+#define FD_EV_ERR_R_BIT 3
#define FD_EV_ACTIVE_W_BIT 4
-#define FD_EV_READY_W_BIT 5
+#define FD_EV_READY_W_BIT 5
+#define FD_EV_SHUT_W_BIT 6
+#define FD_EV_ERR_W_BIT 7
-#define FD_EV_STATUS (FD_EV_ACTIVE | FD_EV_READY)
+#define FD_EV_STATUS (FD_EV_ACTIVE | FD_EV_READY | FD_EV_SHUT | FD_EV_ERR)
#define FD_EV_STATUS_R (FD_EV_STATUS)
#define FD_EV_STATUS_W (FD_EV_STATUS << 4)
@@ -70,6 +76,16 @@
#define FD_EV_READY_W (FD_EV_READY << 4)
#define FD_EV_READY_RW (FD_EV_READY_R | FD_EV_READY_W)
+/* note that when FD_EV_SHUT is set, ACTIVE and READY are cleared */
+#define FD_EV_SHUT_R (FD_EV_SHUT)
+#define FD_EV_SHUT_W (FD_EV_SHUT << 4)
+#define FD_EV_SHUT_RW (FD_EV_SHUT_R | FD_EV_SHUT_W)
+
+/* note that when FD_EV_ERR is set, SHUT is also set */
+#define FD_EV_ERR_R (FD_EV_ERR)
+#define FD_EV_ERR_W (FD_EV_ERR << 4)
+#define FD_EV_ERR_RW (FD_EV_ERR_R | FD_EV_ERR_W)
+
/* This is the value used to mark a file descriptor as dead. This value is
* negative, this is important so that tests on fd < 0 properly match. It