From a1b139e5d448b260b3f7849a5b24f45da45241a1 Mon Sep 17 00:00:00 2001
From: Laurent Bercot <ska-skaware@skarnet.org>
Date: Thu, 20 Aug 2020 14:12:21 +0000
Subject:  Add the notion of essential service

---
 doc/s6-rc-compile.html      |  5 +++++
 doc/s6-rc.html              | 11 ++++++++++-
 src/include/s6-rc/s6rc-db.h |  2 ++
 src/s6-rc/s6-rc-compile.c   | 23 ++++++++++++++++++++++-
 src/s6-rc/s6-rc.c           | 13 ++++++++++---
 5 files changed, 49 insertions(+), 5 deletions(-)

diff --git a/doc/s6-rc-compile.html b/doc/s6-rc-compile.html
index d931b91..b429e8e 100644
--- a/doc/s6-rc-compile.html
+++ b/doc/s6-rc-compile.html
@@ -143,6 +143,11 @@ is ignored, but trailing whitespace is not. Lines starting with a <tt>#</tt>
 character are ignored. The file defines the <em>direct dependencies</em> of
 <em>service</em>, i.e. the services that must be up in order for
 <em>service</em> to work properly. </li>
+ <li> An optional regular file named <tt>flag-essential</tt>. The contents of this
+file are irrelevant, only its presence is tested. If this file exists, the service
+will be marked as essential, which means that a <tt>s6-rc -d change <em>foo</em></tt>
+command will not stop the service. Only a <tt>s6-rc -D change <em>foo</em></tt>
+command will. </li>
 </ul>
 
 <p>
diff --git a/doc/s6-rc.html b/doc/s6-rc.html
index 85a223e..bccc1b5 100644
--- a/doc/s6-rc.html
+++ b/doc/s6-rc.html
@@ -50,7 +50,7 @@ root privileges.
      s6-rc [ -l live ] [ -b ] [ -a ] [ -u | -d ] list <em>servicenames...</em>
      s6-rc [ -l live ] [ -b ] [ -a ] [ -u | -d ] listall <em>servicenames...</em>
      s6-rc [ -l live ] [ -b ] diff
-     s6-rc [ -l live ] [ -b ] [ -a ] [ -u | -d ] [ -p ] [ -v <em>verbosity</em> ] [ -n <em>dryrunthrottle</em> ] [ -t timeout ] change [ <em>servicenames...</em> ]
+     s6-rc [ -l live ] [ -b ] [ -a ] [ -u | -d | -D ] [ -p ] [ -v <em>verbosity</em> ] [ -n <em>dryrunthrottle</em> ] [ -t timeout ] change [ <em>servicenames...</em> ]
 </pre>
 
 <ul>
@@ -122,8 +122,17 @@ Default is <em>up</em>.
 <ul>
  <li> <tt>-u</tt>&nbsp;: up. </li>
  <li> <tt>-d</tt>&nbsp;: down. </li>
+ <li> <tt>-D</tt>&nbsp;: force down. </li>
 </ul>
 
+<p>
+ The <tt>-d</tt> option is what should normally be used to down a set of services.
+If a service is marked as <em>essential</em> (there is a <tt>flag-essential</tt> file
+in its service definition directory), then s6-rc will refuse to stop that service.
+The <tt>-D</tt> option will still force that service to shut down; that option should
+only be used when the machine is going to be stopped.
+</p>
+
 <h3> <tt>s6-rc change</tt> control </h3>
 
 <ul>
diff --git a/src/include/s6-rc/s6rc-db.h b/src/include/s6-rc/s6rc-db.h
index c0d282d..0f03967 100644
--- a/src/include/s6-rc/s6rc-db.h
+++ b/src/include/s6-rc/s6rc-db.h
@@ -12,6 +12,8 @@
 #define S6RC_DB_BANNER_END "\ns6rc-db: end\n"
 #define S6RC_DB_BANNER_END_LEN (sizeof(S6RC_DB_BANNER_END) - 1)
 
+#define S6RC_DB_FLAG_ESSENTIAL 0x00000001U
+
 
 typedef struct s6rc_oneshot_s s6rc_oneshot_t, *s6rc_oneshot_t_ref ;
 struct s6rc_oneshot_s
diff --git a/src/s6-rc/s6-rc-compile.c b/src/s6-rc/s6-rc-compile.c
index 9ce6240..f2b6a84 100644
--- a/src/s6-rc/s6-rc-compile.c
+++ b/src/s6-rc/s6-rc-compile.c
@@ -351,10 +351,30 @@ static uint32_t read_timeout (int dfd, char const *srcdir, char const *name, cha
   return timeout ;
 }
 
+static inline uint32_t read_flags (int dfd, char const *srcdir, char const *name)
+{
+  static char const *files[32] =
+  {
+    "flag-essential",
+    0
+  } ;
+  uint32_t flags = 0 ;
+  for (uint32_t i = 0 ; i < 32 ; i++)
+  {
+    if (!files[i]) break ;
+    if (access_at(dfd, files[i], F_OK, 0) < 0)
+    {
+      if (errno != ENOENT)
+        strerr_diefu6sys(111, "read ", srcdir, "/", name, "/", files[i]) ;
+    }
+    else flags |= i ;
+  }
+  return flags ;
+}
+
 static void add_common (before_t *be, int dfd, char const *srcdir, char const *name, common_t *common, servicetype_t svtype)
 {
   unsigned int dummy ;
-  common->annotation_flags = 0 ;
   add_name(be, srcdir, name, svtype, &dummy, &common->kname) ;
   if (!add_namelist(be, dfd, srcdir, name, "dependencies", &common->depindex, &common->ndeps))
   {
@@ -365,6 +385,7 @@ static void add_common (before_t *be, int dfd, char const *srcdir, char const *n
   }
   common->timeout[0] = read_timeout(dfd, srcdir, name, "timeout-down") ;
   common->timeout[1] = read_timeout(dfd, srcdir, name, "timeout-up") ;
+  common->annotation_flags = read_flags(dfd, srcdir, name) ;
 }
 
 static inline void add_oneshot (before_t *be, int dfd, char const *srcdir, char const *name)
diff --git a/src/s6-rc/s6-rc.c b/src/s6-rc/s6-rc.c
index 76e38da..455bf16 100644
--- a/src/s6-rc/s6-rc.c
+++ b/src/s6-rc/s6-rc.c
@@ -26,7 +26,7 @@
 #include <s6-rc/config.h>
 #include <s6-rc/s6rc.h>
 
-#define USAGE "s6-rc [ -v verbosity ] [ -n dryrunthrottle ] [ -t timeout ] [ -l live ] [ -b ] [ -u | -d ] [ -p ] [ -a ] help|list|listall|diff|change [ servicenames... ]"
+#define USAGE "s6-rc [ -v verbosity ] [ -n dryrunthrottle ] [ -t timeout ] [ -l live ] [ -b ] [ -u | -d | -D ] [ -p ] [ -a ] help|list|listall|diff|change [ servicenames... ]"
 #define dieusage() strerr_dieusage(100, USAGE)
 
 typedef struct pidindex_s pidindex_t ;
@@ -47,6 +47,7 @@ static unsigned char *state ;
 static unsigned int *pendingdeps ;
 static tain_t deadline ;
 static int lameduck = 0 ;
+static int forcestop = 0 ;
 static char dryrun[UINT_FMT] = "" ;
 
 static inline void announce (void)
@@ -261,6 +262,11 @@ static void examine (unsigned int i, int h)
         strerr_warni4x("service ", name, ": already ", h ? "up" : "down") ;
       broadcast_success(i, h) ;
     }
+    else if (!h && !forcestop && db->services[i].flags & S6RC_DB_FLAG_ESSENTIAL)
+    {
+      if (verbosity)
+        strerr_warnw3x("service ", name, " is marked as essential, not stopping it") ;
+    }
     else
     {
       pidindex[npids].pid = i < db->nlong ? start_longrun(i, h) : start_oneshot(i, h) ;
@@ -450,7 +456,7 @@ static inline void print_help (void)
 "s6-rc [ -l live ] [ -a ] list [ servicenames... ]\n"
 "s6-rc [ -l live ] [ -a ] [ -u | -d ] listall [ servicenames... ]\n"
 "s6-rc [ -l live ] diff\n"
-"s6-rc [ -l live ] [ -a ] [ -u | -d ] [ -p ] [ -v verbosity ] [ -t timeout ] [ -n dryrunthrottle ] change [ servicenames... ]\n" ;
+"s6-rc [ -l live ] [ -a ] [ -u | -d | -D ] [ -p ] [ -v verbosity ] [ -t timeout ] [ -n dryrunthrottle ] change [ servicenames... ]\n" ;
   if (buffer_putsflush(buffer_1, help) < 0)
     strerr_diefu1sys(111, "write to stdout") ;
 }
@@ -465,7 +471,7 @@ int main (int argc, char const *const *argv)
     subgetopt_t l = SUBGETOPT_ZERO ;
     for (;;)
     {
-      int opt = subgetopt_r(argc, argv, "v:n:t:l:udpaXb", &l) ;
+      int opt = subgetopt_r(argc, argv, "v:n:t:l:uDdpaXb", &l) ;
       if (opt == -1) break ;
       switch (opt)
       {
@@ -480,6 +486,7 @@ int main (int argc, char const *const *argv)
         case 't' : if (!uint0_scan(l.arg, &t)) dieusage() ; break ;
         case 'l' : live = l.arg ; break ;
         case 'u' : up = 1 ; break ;
+        case 'D' : forcestop = 1 ;
         case 'd' : up = 0 ; break ;
         case 'p' : prune = 1 ; break ;
         case 'a' : selectlive = 1 ; break ;
-- 
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