I've taken a stab at improving kqueue.2 formatting.
Most of the changes are markup fixes.
I used ".Dv NULL" over plain "null" in accordance with
lib/libc/stdlib/malloc.3 rev. 1.113.
I also added a note to the HISTORY section that kqueue()/kevent() have
been available in OpenBSD since 2.9;
the wording matches growfs(8).
I'm not sure how to handle the undocumented EPERM that is returned if a
pledge(2) does not include "proc" when an attempt is made to attach to a
process with EVFILT_PROC.
It does feel somewhat non-obvious, but is noted in neither pledge(2) nor
kqueue(2).
Index: lib/libc/sys/kqueue.2
===================================================================
RCS file: /cvs/src/lib/libc/sys/kqueue.2,v
retrieving revision 1.37
diff -u -p -u -p -r1.37 kqueue.2
--- lib/libc/sys/kqueue.2 13 Jan 2018 17:13:12 -0000 1.37
+++ lib/libc/sys/kqueue.2 2 May 2019 13:28:27 -0000
@@ -67,9 +67,9 @@ is not returned.
Multiple events which trigger the filter do not result in multiple
kevents being placed on the kqueue; instead, the filter will aggregate
the events into a single
-.Li struct kevent .
+.Vt struct kevent .
Calling
-.Fn close
+.Xr close 2
on a file descriptor will remove any kevents that reference the descriptor.
.Pp
.Fn kqueue
@@ -83,8 +83,8 @@ is used to register events with the queu
events to the user.
.Fa changelist
is a pointer to an array of
-.Va kevent
-structures, as defined in
+.Vt struct kevent ,
+as defined in
.In sys/event.h .
All changes contained in the
.Fa changelist
@@ -107,19 +107,23 @@ specified unlike
.Xr select 2 .
If
.Fa timeout
-is a non-null pointer, it specifies a maximum interval to wait
+is not
+.Dv NULL ,
+it specifies a maximum interval to wait
for an event, which will be interpreted as a
-.Li struct timespec .
+.Vt struct timespec .
If
.Fa timeout
-is a null pointer,
+is
+.Dv NULL ,
.Fn kevent
waits indefinitely.
To effect a poll, the
.Fa timeout
-argument should be non-null, pointing to a zero-valued
-.Va timespec
-structure.
+argument should not be
+.Dv NULL ,
+pointing to a zero-valued
+.Vt struct timespec .
The same array may be used for the
.Fa changelist
and
@@ -130,7 +134,7 @@ is a macro which is provided for ease of
kevent structure.
.Pp
The
-.Va kevent
+.Vt kevent
structure is defined as:
.Bd -literal
struct kevent {
@@ -144,28 +148,28 @@ struct kevent {
.Ed
.Pp
The fields of
-.Li struct kevent
+.Vt struct kevent
are:
.Bl -tag -width XXXfilter
-.It ident
+.It Fa ident
Value used to identify this event.
The exact interpretation is determined by the attached filter,
but often is a file descriptor.
-.It filter
+.It Fa filter
Identifies the kernel filter used to process this event.
The pre-defined system filters are described below.
-.It flags
+.It Fa flags
Actions to perform on the event.
-.It fflags
+.It Fa fflags
Filter-specific flags.
-.It data
+.It Fa data
Filter-specific data value.
-.It udata
+.It Fa udata
Opaque user-defined value passed through the kernel unchanged.
.El
.Pp
The
-.Va flags
+.Fa flags
field can contain the following values:
.Bl -tag -width XXXEV_ONESHOT
.It Dv EV_ADD
@@ -200,7 +204,7 @@ to return with
.Dv EV_ERROR
set without draining any pending events after updating events in the kqueue.
When a filter is successfully added the
-.Va data
+.Fa data
field will be zero.
This flag is useful for making bulk changes to a kqueue.
.It Dv EV_ONESHOT
@@ -222,9 +226,9 @@ below.
.Pp
The predefined system filters are listed below.
Arguments may be passed to and from the filter via the
-.Va fflags
+.Fa fflags
and
-.Va data
+.Fa data
fields in the kevent structure.
.Bl -tag -width EVFILT_SIGNAL
.It Dv EVFILT_READ
@@ -235,9 +239,9 @@ on the descriptor type.
.Bl -tag -width 2n
.It Sockets
Sockets which have previously been passed to
-.Fn listen
+.Xr listen 2
return when there is an incoming connection pending.
-.Va data
+.Fa data
contains the size of the listen backlog.
.Pp
Other socket descriptors return when there is data to be read,
@@ -248,47 +252,47 @@ This may be overridden with a per-filter
time the filter is added by setting the
.Dv NOTE_LOWAT
flag in
-.Va fflags ,
+.Fa fflags ,
and specifying the new low water mark in
-.Va data .
+.Fa data .
On return,
-.Va data
+.Fa data
contains the number of bytes in the socket buffer.
.Pp
If the read direction of the socket has shutdown, then the filter
also sets
.Dv EV_EOF
in
-.Va flags ,
+.Fa flags ,
and returns the socket error (if any) in
-.Va fflags .
+.Fa fflags .
It is possible for EOF to be returned (indicating the connection is gone)
while there is still data pending in the socket buffer.
.It Vnodes
Returns when the file pointer is not at the end of file.
-.Va data
+.Fa data
contains the offset from current position to end of file,
and may be negative.
If
.Dv NOTE_EOF
is set in
-.Va fflags ,
+.Fa fflags ,
.Fn kevent
will also return when the file pointer is at the end of file.
The end of file condition is indicated by the presence of
.Dv NOTE_EOF
in
-.Va fflags
+.Fa fflags
on return.
.It "FIFOs, Pipes"
Returns when there is data to read;
-.Va data
+.Fa data
contains the number of bytes available.
.Pp
When the last writer disconnects, the filter will set
.Dv EV_EOF
in
-.Va flags .
+.Fa flags .
This may be cleared by passing in
.Dv EV_CLEAR ,
at which point the filter will resume waiting for data to become
@@ -298,14 +302,14 @@ Returns when the BPF buffer is full, the
when the BPF has
.Dq immediate mode
enabled and there is any data to read;
-.Va data
+.Fa data
contains the number of bytes available.
.El
.It Dv EVFILT_WRITE
Takes a descriptor as the identifier, and returns whenever
it is possible to write to the descriptor.
For sockets, pipes, and FIFOs,
-.Va data
+.Fa data
will contain the amount of space remaining in the write buffer.
The filter will set
.Dv EV_EOF
@@ -346,12 +350,12 @@ case.
.\"and should be considered deprecated.
.It Dv EVFILT_VNODE
Takes a file descriptor as the identifier and the events to watch for in
-.Va fflags ,
+.Fa fflags ,
and returns when one or more of the requested events occurs on the descriptor.
The events to monitor are:
.Bl -tag -width XXNOTE_RENAME
.It Dv NOTE_DELETE
-.Fn unlink
+.Xr unlink 2
was called on the file referenced by the descriptor.
.It Dv NOTE_WRITE
A write occurred on the file referenced by the descriptor.
@@ -372,12 +376,12 @@ or the underlying file system was unmoun
.El
.Pp
On return,
-.Va fflags
+.Fa fflags
contains the events which triggered the filter.
.It Dv EVFILT_PROC
Takes the process ID to monitor as the identifier and the events to watch for
in
-.Va fflags ,
+.Fa fflags ,
and returns when the process performs one or more of the requested events.
If a process can normally see another process, it can attach an event to it.
The events to monitor are:
@@ -385,51 +389,51 @@ The events to monitor are:
.It Dv NOTE_EXIT
The process has exited.
The exit status will be stored in
-.Va data
+.Fa data
in the same format as the status set by
.Xr wait 2 .
.It Dv NOTE_FORK
The process has called
-.Fn fork .
+.Xr fork 2 .
.It Dv NOTE_EXEC
The process has executed a new process via
.Xr execve 2
or similar call.
.It Dv NOTE_TRACK
Follow a process across
-.Fn fork
+.Xr fork 2
calls.
The parent process will return with
.Dv NOTE_FORK
set in the
-.Va fflags
+.Fa fflags
field, while the child process will return with
.Dv NOTE_CHILD
set in
-.Va fflags
+.Fa fflags
and the parent PID in
-.Va data .
+.Fa data .
.It Dv NOTE_TRACKERR
This flag is returned if the system was unable to attach an event to
the child process, usually due to resource limitations.
.El
.Pp
On return,
-.Va fflags
+.Fa fflags
contains the events which triggered the filter.
.It Dv EVFILT_SIGNAL
Takes the signal number to monitor as the identifier and returns
when the given signal is delivered to the process.
This coexists with the
-.Fn signal
+.Xr signal 3
and
-.Fn sigaction
+.Xr sigaction 2
facilities, and has a lower precedence.
The filter will record all attempts to deliver a signal to a process,
even if the signal has been marked as
.Dv SIG_IGN .
Event notification happens after normal signal delivery processing.
-.Va data
+.Fa data
returns the number of times the signal has occurred since the last call to
.Fn kevent .
This filter automatically sets the
@@ -437,15 +441,15 @@ This filter automatically sets the
flag internally.
.It Dv EVFILT_TIMER
Establishes an arbitrary timer identified by
-.Va ident .
+.Fa ident .
When adding a timer,
-.Va data
+.Fa data
specifies the timeout period in milliseconds.
The timer will be periodic unless
.Dv EV_ONESHOT
is specified.
On return,
-.Va data
+.Fa data
contains the number of times the timeout has expired since the last call to
.Fn kevent .
This filter automatically sets the
@@ -453,7 +457,7 @@ This filter automatically sets the
flag internally.
.It Dv EVFILT_DEVICE
Takes a descriptor as the identifier and the events to watch for in
-.Va fflags ,
+.Fa fflags ,
and returns when one or more of the requested events occur on the
descriptor.
The events to monitor are:
@@ -463,14 +467,16 @@ A device change event has occurred, e.g.
.El
.Pp
On return,
-.Va fflags
+.Fa fflags
contains the events which triggered the filter.
.El
.Sh RETURN VALUES
.Fn kqueue
creates a new kernel event queue and returns a file descriptor.
If there was an error creating the kernel event queue, a value of -1 is
-returned and errno set.
+returned and
+.Va errno
+set.
.Pp
.Fn kevent
returns the number of events placed in the
@@ -486,13 +492,11 @@ then the event will be placed in the
with
.Dv EV_ERROR
set in
-.Va flags
+.Fa flags
and the system error in
-.Va data .
-Otherwise,
-.Dv -1
-will be returned, and
-.Dv errno
+.Fa data .
+Otherwise, -1 will be returned, and
+.Va errno
will be set to indicate the error condition.
If the time limit expires, then
.Fn kevent
@@ -518,8 +522,7 @@ function fails if:
The process does not have permission to register a filter.
.It Bq Er EFAULT
There was an error reading or writing the
-.Va kevent
-structure.
+.Vt struct kevent .
.It Bq Er EBADF
The specified descriptor is invalid.
.It Bq Er EINTR
@@ -548,7 +551,9 @@ The
and
.Fn kevent
functions first appeared in
-.Fx 4.1 .
+.Fx 4.1
+and have been available since
+.Ox 2.9 .
.Sh AUTHORS
The
.Fn kqueue
