services: dovecot: Allow to set 'client-limit'.

* doc/guix.texi (Mail Services): Update accordingly.
* gnu/services/mail.scm (service-configuration)[client-limit]: New field.
(dovecot-configuration)[services]: Set 'client-limit' to its correct default
value.

doc/guix.texi

@@ -14349,6 +14349,16 @@ Defaults to @samp{#t}.
 
 @end deftypevr
 
+@deftypevr {@code{service-configuration} parameter} non-negative-integer client-limit
+Maximum number of simultaneous client connections per process.  Once
+this number of connections is received, the next incoming connection
+will prompt Dovecot to spawn another process.  If set to 0,
+@code{default-client-limit} is used instead.
+
+Defaults to @samp{0}.
+
+@end deftypevr
+
 @deftypevr {@code{service-configuration} parameter} non-negative-integer service-count
 Number of connections to handle before starting a new process.
 Typically the only useful values are 0 (unlimited) or 1.  1 is more

gnu/services/mail.scm

@@ -1,6 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2015 Andy Wingo <wingo@igalia.com>
-;;; Copyright © 2017 Clément Lassieur <clement@lassieur.org>
+;;; Copyright © 2017, 2018 Clément Lassieur <clement@lassieur.org>
 ;;; Copyright © 2017 Carlo Zancanaro <carlo@zancanaro.id.au>
 ;;; Copyright © 2017 Tobias Geerinckx-Rice <me@tobias.gr>
 ;;;
@@ -290,6 +290,12 @@ the section name.")
    "Listeners for the service.  A listener is either an
 @code{unix-listener-configuration}, a @code{fifo-listener-configuration}, or
 an @code{inet-listener-configuration}.")
+  (client-limit
+   (non-negative-integer 0)
+   "Maximum number of simultaneous client connections per process.  Once this
+number of connections is received, the next incoming connection will prompt
+Dovecot to spawn another process.  If set to 0, @code{default-client-limit} is
+used instead.")
   (service-count
    (non-negative-integer 1)
    "Number of connections to handle before starting a new process.
@@ -475,6 +481,7 @@ complex, customize the address and port fields of the
     (list
      (service-configuration
       (kind "imap-login")
+      (client-limit 0)
       (listeners
        (list
         (inet-listener-configuration (protocol "imap") (port 143) (ssl? #f))
@@ -487,10 +494,15 @@ complex, customize the address and port fields of the
         (inet-listener-configuration (protocol "pop3s") (port 995) (ssl? #t)))))
      (service-configuration
       (kind "lmtp")
+      (client-limit 1)
       (listeners
        (list (unix-listener-configuration (path "lmtp") (mode "0666")))))
-     (service-configuration (kind "imap"))
-     (service-configuration (kind "pop3"))
+     (service-configuration
+      (kind "imap")
+      (client-limit 1))
+     (service-configuration
+      (kind "pop3")
+      (client-limit 1))
      (service-configuration (kind "auth")
       ;; In what could be taken to be a bug, the default value of 1 for
       ;; service-count makes it so that a PAM auth worker can't fork off
@@ -501,10 +513,15 @@ complex, customize the address and port fields of the
       ;; is the default for all other services.  As a hack, bump this value to
       ;; 30.
       (service-count 30)
+      (client-limit 0)
       (listeners
        (list (unix-listener-configuration (path "auth-userdb")))))
-     (service-configuration (kind "auth-worker"))
-     (service-configuration (kind "dict")
+     (service-configuration
+      (kind "auth-worker")
+      (client-limit 1))
+     (service-configuration
+      (kind "dict")
+      (client-limit 1)
       (listeners (list (unix-listener-configuration (path "dict")))))))
    "List of services to enable.  Available services include @samp{imap},
 @samp{imap-login}, @samp{pop3}, @samp{pop3-login}, @samp{auth}, and