libxl: Expose functions for helping with subprocesses.

 * Expose libxl_fork in libxl_utils.h
 * Expose libxl_pipe in libxl_utils.h
 * Make libxl_exec put SIGPIPE back (so that libxl callers may
    have SIGPIPE ignored)

xl would like to use libxl_fork (which is like fork(2) except that it
logs errors) and also a similar function libxl_pipe.  So put these in
libxl_utils.[ch] and use them in libxl.c as appropriate, to avoid
having to duplicate code between xl and libxl.

Also, make sure that subprocesses spawned by libxl have SIGPIPE set
back to SIG_DFL as they are entitled to expect.  This means that a
libxl caller which sets SIGPIPE to SIG_IGN is no longer buggy.  (This
is relevant for xl migration, because xl would like to be such a
caller.)

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>

1 files changed, 5 insertions, 13 deletions

diff --git a/tools/libxl/libxl_exec.c b/tools/libxl/libxl_exec.c
index e8cc74c7da..6d4a5c5115 100644
--- a/tools/libxl/libxl_exec.c
+++ b/tools/libxl/libxl_exec.c
@@ -30,19 +30,6 @@
 #include "libxl.h"
 #include "libxl_internal.h"
 
-static pid_t libxl_fork(struct libxl_ctx *ctx)
-{
-    pid_t pid;
-
-    pid = fork();
-    if (pid == -1) {
-        XL_LOG_ERRNO(ctx, XL_LOG_ERROR, "fork failed");
-        return -1;
-    }
-
-    return pid;
-}
-
 static int call_waitpid(pid_t (*waitpid_cb)(pid_t, int *, int), pid_t pid, int *status, int options)
 {
     return (waitpid_cb) ? waitpid_cb(pid, status, options) : waitpid(pid, status, options);
@@ -61,6 +48,11 @@ void libxl_exec(int stdinfd, int stdoutfd, int stderrfd, char *arg0, char **args
         dup2(stderrfd, STDERR_FILENO);
     for (i = 4; i < 256; i++)
         close(i);
+
+    signal(SIGPIPE, SIG_DFL);
+    /* in case our caller set it to IGN.  subprocesses are entitled
+     * to assume they got DFL. */
+
     execv(arg0, args);
     _exit(-1);
 }