3 files changed, 144 insertions, 11 deletions
diff --git a/doc/man/flow_alloc.3 b/doc/man/flow_alloc.3
index dbe5323c..8a9b5f5b 100644
--- a/doc/man/flow_alloc.3
+++ b/doc/man/flow_alloc.3
@@ -62,10 +62,60 @@ The \fBflow_dealloc\fR() function will release any resources
 associated with the flow. This call may block and keep reliable flows
 active until all packets are acknowledged.
 
-A \fBqosspec_t\fR specifies the following QoS characteristics of a
-flow:
-
-TODO: specify a qosspec_t
+A \fBqosspec_t\fR specifies the QoS characteristics of a flow.
+The fields are:
+
+.TP
+\fBdelay\fR (ms)
+Maximum one-way delay.
+.TP
+\fBbandwidth\fR (bits/s)
+Minimum bandwidth.
+.TP
+\fBavailability\fR
+Class of 9s (e.g. 5 = 99.999%).
+.TP
+\fBloss\fR
+Tolerated packet loss; 0 selects reliable delivery.
+.TP
+\fBber\fR
+Tolerated bit error rate (errors per billion bits); 0 enables an
+end-to-end integrity check (corrupted packets are dropped).
+.TP
+\fBservice\fR
+Framing / reliability class: \fBSVC_RAW\fR (0) disables FRCT;
+\fBSVC_MESSAGE\fR (1) preserves SDU boundaries; \fBSVC_STREAM\fR (2) is
+a byte stream with no SDU boundaries. \fBSVC_STREAM\fR requires
+\fIloss\fR = 0; otherwise
+\fBflow_alloc\fR()/\fBflow_accept\fR() returns \fB-EINVAL\fR.
+.TP
+\fBmax_gap\fR (ms)
+Maximum tolerated inter-packet gap. Packets exceeding the gap
+budget are dropped under the real-time cubes.
+.TP
+\fBtimeout\fR (ms)
+Peer-liveness timeout; 0 disables. Only applies when FRCT is
+enabled (service > 0).
+
+.PP
+The library provides predefined cubes:
+
+.TP
+\fBqos_raw\fR
+No guarantees, no integrity check.
+.TP
+\fBqos_raw_safe\fR
+Best-effort with end-to-end integrity (ber = 0).
+.TP
+\fBqos_rt\fR / \fBqos_rt_safe\fR
+Real-time messages, optimised for latency over reliability;
+\fBqos_rt_safe\fR adds an end-to-end integrity check.
+.TP
+\fBqos_msg\fR
+Reliable, SDU-preserving delivery.
+.TP
+\fBqos_stream\fR
+Reliable byte stream; no SDU boundaries are preserved.
 
 .SH RETURN VALUE
 
@@ -117,13 +167,39 @@ _
 \fBflow_dealloc\fR() & Thread safety & MT-Safe
 .TE
 
+.SH NOTES
+The returned file descriptor is subject to a single-reader and
+single-writer discipline \(em at most one thread may call
+.BR flow_read ()
+(or monitor the fd via
+.BR fevent ())
+and at most one thread may call
+.BR flow_write ()
+concurrently. See
+.BR flow_read (3),
+.BR flow_write (3),
+and
+.BR fevent (3)
+for details.
+.PP
+.BR flow_dealloc ()
+must not be called concurrently with any thread that is inside
+.BR flow_read (),
+.BR flow_write (),
+.BR fevent (),
+or any other Ouroboros library call on the same fd; the result is
+undefined behaviour. Applications must serialise teardown with
+in-flight use, e.g. by signalling worker threads to drop the fd
+before calling
+.BR flow_dealloc ().
+
 .SH TERMINOLOGY
 Please see \fBouroboros-glossary\fR(7).
 
 .SH SEE ALSO
 
-.BR fccntl "(3), " flow_read "(3), " fqueue "(3), " fset "(3), " \
-ouroboros (8)
+.BR fccntl "(3), " fevent "(3), " flow_read "(3), " flow_write "(3), " \
+fqueue "(3), " fset "(3), " ouroboros (8)
 
 .SH COLOPHON
 This page is part of the Ouroboros project, found at
diff --git a/doc/man/flow_read.3 b/doc/man/flow_read.3
index acc1f61e..d4a5e883 100644
--- a/doc/man/flow_read.3
+++ b/doc/man/flow_read.3
@@ -39,8 +39,7 @@ end of the datagram.
 
 On success, \fBflow_write\fR() returns the number of bytes written. On
 failure, a negative value indicating the error will be returned.
-Partial writes needs to be explicitly enabled. Passing a
-NULL pointer for \fIbuf\fR returns 0 with no other effects.
+Passing a NULL pointer for \fIbuf\fR returns 0 with no other effects.
 
 .SH ERRORS
 .B -EINVAL
@@ -62,7 +61,8 @@ The flow has been reported down.
 The flow's peer is unresponsive (flow timed out).
 
 .B -EMSGSIZE
-The buffer was too large to be written.
+The received packet does not fit in the caller's buffer and partial
+reads are disabled (see \fBfccntl\fR(3), \fBFLOWFRNOPART\fR).
 
 .SH ATTRIBUTES
 
@@ -74,11 +74,47 @@ LB|LB|LB
 L|L|L.
 Interface & Attribute & Value
 _
-\fBflow_read\fR() & Thread safety & MT-Safe
+\fBflow_read\fR() & Thread safety & MT-Safe race:fd
 _
-\fBflow_write\fR() & Thread safety & MT-Safe
+\fBflow_write\fR() & Thread safety & MT-Safe race:fd
 .TE
 
+.SH THREAD SAFETY
+Only one thread may call
+.BR flow_read ()
+on a given file descriptor at any time. Partial-read state kept
+across calls assumes a single logical reader; two threads racing
+.BR flow_read ()
+on the same fd is undefined behaviour. Likewise, only one thread
+may call
+.BR flow_write ()
+on a given fd at a time; two writer threads on the same fd is
+undefined behaviour.
+.PP
+Combining a writer thread with a reader thread (one thread calling
+.BR flow_write (),
+another calling
+.BR flow_read ()
+or
+.BR fevent ())
+is permitted and safe. The writer does not need a dedicated reader
+thread \(em when the FRCT send window fills,
+.BR flow_write ()
+drives its own inbound rx draining internally to process incoming
+ACKs and reopen the window, clamped by the caller's
+.BR fccntl (3)
+send-timeout if any.
+.PP
+Monitoring the same fd via
+.BR fevent ()
+from a different thread is well-defined but races: events reported
+by
+.BR fevent ()
+may already have been consumed by the racing
+.BR flow_read (),
+so the second reader may then block. See
+.BR fevent (3).
+
 .SH TERMINOLOGY
 Please see \fBouroboros-glossary\fR(7).
 
diff --git a/doc/man/fqueue.3 b/doc/man/fqueue.3
index 72a0bc25..f2fb8c9f 100644
--- a/doc/man/fqueue.3
+++ b/doc/man/fqueue.3
@@ -116,6 +116,27 @@ _
 \fBfevent\fR() & Thread safety & MT-Safe
 .TE
 
+.SH THREAD SAFETY
+.BR fevent ()
+and
+.BR flow_read ()
+on the same fd from distinct threads is well-defined but races:
+events reported by
+.BR fevent ()
+may already have been consumed by the racing
+.BR flow_read (),
+so the reader may then block. Same shape as
+.BR select (2)
++
+.BR read (2)
+from distinct threads. The intended pattern is that the thread
+invoking
+.BR fevent ()
+is the same thread that calls
+.BR flow_read ()
+on the fds returned by
+.BR fqueue_next ().
+
 .SH TERMINOLOGY
 Please see \fBouroboros-glossary\fR(7).