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