[libvirt] [PATCH v3 01/13] virprocess: Introduce virProcessRunInFork

Michal Privoznik mprivozn at redhat.com
Wed Oct 17 09:06:43 UTC 2018


This new helper can be used to spawn a child process and run
passed callback from it. This will come handy esp. if the
callback is not thread safe.

Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---
 src/libvirt_private.syms |  1 +
 src/util/virprocess.c    | 81 ++++++++++++++++++++++++++++++++++++++++
 src/util/virprocess.h    | 16 ++++++++
 3 files changed, 98 insertions(+)

diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 335210c31d..e2dc85310a 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -2625,6 +2625,7 @@ virProcessKill;
 virProcessKillPainfully;
 virProcessKillPainfullyDelay;
 virProcessNamespaceAvailable;
+virProcessRunInFork;
 virProcessRunInMountNamespace;
 virProcessSchedPolicyTypeFromString;
 virProcessSchedPolicyTypeToString;
diff --git a/src/util/virprocess.c b/src/util/virprocess.c
index 3883c708fc..51b9ccb1bb 100644
--- a/src/util/virprocess.c
+++ b/src/util/virprocess.c
@@ -1165,6 +1165,87 @@ virProcessRunInMountNamespace(pid_t pid,
 }
 
 
+static int
+virProcessForkHelper(int errfd,
+                     pid_t pid,
+                     virProcessForkCallback cb,
+                     void *opaque)
+{
+    if (cb(pid, opaque) < 0) {
+        virErrorPtr err = virGetLastError();
+        if (err) {
+            size_t len = strlen(err->message) + 1;
+            ignore_value(safewrite(errfd, err->message, len));
+        }
+
+        return -1;
+    }
+
+    return 0;
+}
+
+
+/**
+ * virProcessRunInFork:
+ * @cb: callback to run
+ * @opaque: opaque data to @cb
+ *
+ * Do the fork and run @cb in the child. This can be used when
+ * @cb does something thread unsafe, for instance. However, due
+ * to possible signal propagation @cb should only call async
+ * signal safe functions. On return, the returned value is either
+ * -1 with error message reported if something went bad in the
+ *  parent, if child has died from a signal or if the child
+ *  returned EXIT_CANCELED. Otherwise the returned value is the
+ *  exit status of the child.
+ */
+int
+virProcessRunInFork(virProcessForkCallback cb,
+                    void *opaque)
+{
+    int ret = -1;
+    pid_t child = -1;
+    pid_t parent = getpid();
+    int errfd[2] = { -1, -1 };
+
+    if (pipe2(errfd, O_CLOEXEC) < 0) {
+        virReportSystemError(errno, "%s",
+                             _("Cannot create pipe for child"));
+        return -1;
+    }
+
+    if ((child = virFork()) < 0)
+        goto cleanup;
+
+    if (child == 0) {
+        VIR_FORCE_CLOSE(errfd[0]);
+        ret = virProcessForkHelper(errfd[1], parent, cb, opaque);
+        VIR_FORCE_CLOSE(errfd[1]);
+        _exit(ret < 0 ? EXIT_CANCELED : ret);
+    } else {
+        int status;
+        VIR_AUTOFREE(char *) buf = NULL;
+
+        VIR_FORCE_CLOSE(errfd[1]);
+        ignore_value(virFileReadHeaderFD(errfd[0], 1024, &buf));
+        ret = virProcessWait(child, &status, false);
+        if (!ret) {
+            ret = status == EXIT_CANCELED ? -1 : status;
+            if (ret) {
+                virReportError(VIR_ERR_INTERNAL_ERROR,
+                               _("child reported: %s"),
+                               NULLSTR(buf));
+            }
+        }
+    }
+
+ cleanup:
+    VIR_FORCE_CLOSE(errfd[0]);
+    VIR_FORCE_CLOSE(errfd[1]);
+    return ret;
+}
+
+
 #if defined(HAVE_SYS_MOUNT_H) && defined(HAVE_UNSHARE)
 int
 virProcessSetupPrivateMountNS(void)
diff --git a/src/util/virprocess.h b/src/util/virprocess.h
index 5faa0892fe..1bae8c9212 100644
--- a/src/util/virprocess.h
+++ b/src/util/virprocess.h
@@ -93,6 +93,22 @@ int virProcessRunInMountNamespace(pid_t pid,
                                   virProcessNamespaceCallback cb,
                                   void *opaque);
 
+/**
+ * virProcessForkCallback:
+ * @pid: parent's pid
+ * @opaque: opaque data
+ *
+ * Callback to run in fork()-ed process.
+ *
+ * Returns: 0 on success,
+ *         -1 on error (treated as EXIT_CANCELED)
+ */
+typedef int (*virProcessForkCallback)(pid_t pid,
+                                      void *opaque);
+
+int virProcessRunInFork(virProcessForkCallback cb,
+                        void *opaque);
+
 int virProcessSetupPrivateMountNS(void);
 
 int virProcessSetScheduler(pid_t pid,
-- 
2.18.1




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