ash: additional support for background jobs

The rationale for the jobs builtin in POSIX notes:

   The jobs utility is not dependent on the job control option,
   as are the seemingly related bg and fg utilities because jobs
   is useful for examining background jobs, regardless of the
   condition of job control. When the user has invoked a set +m
   command and job control has been turned off, jobs can still be
   used to examine the background jobs associated with that current
   session. Similarly, kill can then be used to kill background
   jobs with kill %<background job number>.

Although ash in busybox-w32 doesn't support job control it can
handle background jobs.

Allow the ASH_JOB_CONTROL setting to enable certain features:

- the jobs builtin;
- killing of jobs by job id in the kill builtin;
- monitoring of changes to jobs.

Since process groups aren't supported it's necessary to kill the
processes constituting a background job individually.  When doing
this we ask kill(2) to kill all children too.

3 files changed, 44 insertions, 11 deletions

diff --git a/configs/mingw32_defconfig b/configs/mingw32_defconfig
index 195020151..d41899fdc 100644
--- a/configs/mingw32_defconfig
+++ b/configs/mingw32_defconfig
@@ -1131,7 +1131,7 @@ CONFIG_ASH_INTERNAL_GLOB=y
 CONFIG_ASH_BASH_COMPAT=y
 # CONFIG_ASH_BASH_SOURCE_CURDIR is not set
 CONFIG_ASH_BASH_NOT_FOUND_HOOK=y
-# CONFIG_ASH_JOB_CONTROL is not set
+CONFIG_ASH_JOB_CONTROL=y
 CONFIG_ASH_ALIAS=y
 CONFIG_ASH_RANDOM_SUPPORT=y
 CONFIG_ASH_EXPAND_PRMT=y
diff --git a/configs/mingw64_defconfig b/configs/mingw64_defconfig
index aa704fe75..449f16ae6 100644
--- a/configs/mingw64_defconfig
+++ b/configs/mingw64_defconfig
@@ -1131,7 +1131,7 @@ CONFIG_ASH_INTERNAL_GLOB=y
 CONFIG_ASH_BASH_COMPAT=y
 # CONFIG_ASH_BASH_SOURCE_CURDIR is not set
 CONFIG_ASH_BASH_NOT_FOUND_HOOK=y
-# CONFIG_ASH_JOB_CONTROL is not set
+CONFIG_ASH_JOB_CONTROL=y
 CONFIG_ASH_ALIAS=y
 CONFIG_ASH_RANDOM_SUPPORT=y
 CONFIG_ASH_EXPAND_PRMT=y
diff --git a/shell/ash.c b/shell/ash.c
index fafbeb86e..6be99864f 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -24,7 +24,7 @@
  * - command without ".exe" extension is still understood as executable
  * - shell scripts on the path are detected by the presence of '#!'
  * - both / and \ are supported in PATH. Usually you must use /
- * - job control doesn't work
+ * - job control doesn't work, though the jobs builtin is available
  * - trap doesn't work for signals, only EXIT
  * - /dev/null is supported for redirection
  * - fake $PPID
@@ -212,7 +212,17 @@
 
 #define PROFILE 0
 
+/*
+ * Only one of JOBS or JOBS_WIN32 is enabled at a time (or neither).
+ * JOBS_WIN32 doesn't enable job control, just some job-related features.
+ */
+#if ENABLE_PLATFORM_MINGW32
+#define JOBS_WIN32 ENABLE_ASH_JOB_CONTROL
+#define JOBS 0
+#else
+#define JOBS_WIN32 0
 #define JOBS ENABLE_ASH_JOB_CONTROL
+#endif
 
 #include <fnmatch.h>
 #include <sys/times.h>
@@ -4112,10 +4122,13 @@ static int forkshell(struct job *, union node *, int);
 #endif
 static int waitforjob(struct job *);
 
-#if !JOBS
+#if !JOBS && !JOBS_WIN32
 enum { doing_jobctl = 0 };
 #define setjobctl(on) do {} while (0)
-#else
+#elif JOBS_WIN32
+static smallint doing_jobctl; //references:8
+#define setjobctl(on) do { if (rootshell) doing_jobctl = on; } while (0)
+#else /* JOBS */
 static smallint doing_jobctl; //references:8
 static void setjobctl(int);
 #endif
@@ -4404,7 +4417,7 @@ set_curjob(struct job *jp, unsigned mode)
         }
 }
 
-#if JOBS || DEBUG
+#if JOBS || JOBS_WIN32 || DEBUG
 static int
 jobno(const struct job *jp)
 {
@@ -4617,7 +4630,9 @@ setjobctl(int on)
         ttyfd = fd;
         doing_jobctl = on;
 }
+#endif
 
+#if JOBS || JOBS_WIN32
 static int FAST_FUNC
 killcmd(int argc, char **argv)
 {
@@ -4647,8 +4662,10 @@ killcmd(int argc, char **argv)
                                  * sh -c 'true|sleep 1 & sleep 2; kill %1'
                                  */
                                 n = jp->nprocs; /* can't be 0 (I hope) */
+#if !ENABLE_PLATFORM_MINGW32
                                 if (jp->jobctl)
                                         n = 1;
+#endif
                                 dst = alloca(n * sizeof(int)*4);
                                 argv[i] = dst;
                                 for (j = 0; j < n; j++) {
@@ -4663,7 +4680,11 @@ killcmd(int argc, char **argv)
                                          * leading space. Needed to not confuse
                                          * negative pids with "kill -SIGNAL_NO" syntax
                                          */
+#if !ENABLE_PLATFORM_MINGW32
                                         dst += sprintf(dst, jp->jobctl ? " -%u" : " %u", (int)ps->ps_pid);
+#else
+                                        dst += sprintf(dst, " -%u", (int)ps->ps_pid);
+#endif
                                 }
                                 *dst = '\0';
                         }
@@ -4671,7 +4692,9 @@ killcmd(int argc, char **argv)
         }
         return kill_main(argc, argv);
 }
+#endif
 
+#if JOBS
 static void
 showpipe(struct job *jp /*, FILE *out*/)
 {
@@ -5048,7 +5071,7 @@ dowait(int block, struct job *jp)
 #endif
 }
 
-#if JOBS
+#if JOBS || JOBS_WIN32
 static void
 showjob(struct job *jp, int mode)
 {
@@ -5085,8 +5108,10 @@ showjob(struct job *jp, int mode)
                 col += sizeof("Running") - 1;
         } else {
                 int status = psend[-1].ps_status;
+#if !ENABLE_PLATFORM_MINGW32
                 if (jp->state == JOBSTOPPED)
                         status = jp->stopstatus;
+#endif
                 col += sprint_status48(s + col, status, 0);
         }
         /* By now, "[JOBID]*  [maybe PID] STATUS" is printed */
@@ -5107,12 +5132,16 @@ showjob(struct job *jp, int mode)
                 if (mode & SHOW_PIDS)
                         col = fmtstr(s, 48, "\n%*c%d ", indent_col, ' ', ps->ps_pid) - 1;
  start:
+#if !ENABLE_PLATFORM_MINGW32
                 fprintf(out, "%s%*c%s%s",
                                 s,
                                 33 - col >= 0 ? 33 - col : 0, ' ',
                                 ps == jp->ps ? "" : "| ",
                                 ps->ps_cmd
                 );
+#else
+                fprintf(out, "%s", s);
+#endif
         } while (++ps != psend);
         newline_and_flush(out);
 
@@ -5369,7 +5398,7 @@ makejob(/*union node *node,*/ int nprocs)
                         break;
                 if (jp->state != JOBDONE || !jp->waited)
                         continue;
-#if JOBS
+#if JOBS || JOBS_WIN32
                 if (doing_jobctl)
                         continue;
 #endif
@@ -10997,7 +11026,7 @@ static const struct builtincmd builtintab[] = {
 #if MAX_HISTORY
         { BUILTIN_NOSPEC        "history" , historycmd },
 #endif
-#if JOBS
+#if JOBS || JOBS_WIN32
         { BUILTIN_REGULAR       "jobs"    , jobscmd    },
         { BUILTIN_REGULAR       "kill"    , killcmd    },
 #endif
@@ -11039,7 +11068,7 @@ static const struct builtincmd builtintab[] = {
         /* [ */         1 * ENABLE_ASH_TEST + \
         /* [[ */        1 * BASH_TEST2 + \
         /* alias */     1 * ENABLE_ASH_ALIAS + \
-        /* bg */        1 * ENABLE_ASH_JOB_CONTROL + \
+        /* bg */        1 * JOBS + \
         /* break cd cddir  */   3)
 #define EVALCMD (COMMANDCMD + \
         /* command */   1 * ENABLE_ASH_CMDCMD + \
@@ -14365,7 +14394,7 @@ cmdloop(int top)
                 int skip;
 
                 setstackmark(&smark);
-#if JOBS
+#if JOBS || JOBS_WIN32
                 if (doing_jobctl)
                         showjobs(SHOW_CHANGED|SHOW_STDERR);
 #endif
@@ -16735,6 +16764,10 @@ forkshell_init(const char *idstr)
         else {
                 SetConsoleCtrlHandler(ctrl_handler, TRUE);
         }
+#if JOBS_WIN32
+        /* do job control only in root shell */
+        doing_jobctl = 0;
+#endif
  end:
         forkshell_child(fs);
 }