Introduce a sub system that can store io cookies for file descriptors, thread safely so

1 files changed, 52 insertions, 0 deletions

diff --git a/ot_fdstate.h b/ot_fdstate.h
new file mode 100644
index 0000000..2693a3b
--- /dev/null
+++ b/ot_fdstate.h
@@ -0,0 +1,52 @@
+/* This software was written by Dirk Engling <erdgeist@erdgeist.org>
+   It is considered beerware. Prost. Skol. Cheers or whatever.
+
+   $id$ */
+
+#ifndef OT_FDSTATE_H__
+#define OT_FDSTATE_H__
+
+#include <stdint.h>
+
+#include "trackerlogic.h"
+
+/* What the tracker knows about a file descriptor: who owns it, when it
+   should be given up on, and whether anyone is working on it right now.
+
+   A descriptor number says nothing about identity, since the kernel hands
+   the same number out again as soon as it is closed. Every slot therefore
+   carries a generation that is bumped when the descriptor is given up, and
+   every caller that was told about a descriptor has to say which generation
+   it was told about. A caller holding a stale generation is turned away
+   instead of being handed somebody else's connection.
+
+   The table is sized once from RLIMIT_NOFILE and never moves, so looking a
+   descriptor up needs no synchronisation at all. */
+
+int      fdstate_init(void);
+void     fdstate_deinit(void);
+size_t   fdstate_slots(void);
+
+/* Take a freshly accepted descriptor into the table and return the
+   generation to quote when asking for it back. expiry of 0 never expires. */
+uint32_t fdstate_open(int fd, void *cookie, ot_time expiry);
+
+/* Ask for exclusive use. Returns 0 if the descriptor has been recycled since
+   generation was handed out, or if somebody else is using it. */
+int      fdstate_claim(int fd, uint32_t generation);
+void     fdstate_release(int fd);
+
+/* The cleaner's side of the same thing: takes the descriptor only if nobody
+   is working on it and it really has expired. Never waits. */
+int      fdstate_claim_expired(int fd, ot_time now);
+
+/* Give the descriptor up. The generation is bumped here, which has to happen
+   before close(2) so that the kernel cannot reissue the number while events
+   quoting the old generation are still in flight. */
+void     fdstate_close(int fd);
+
+/* Both only valid while the caller holds the descriptor. */
+void    *fdstate_cookie(int fd);
+void     fdstate_set_expiry(int fd, ot_time expiry);
+
+#endif