Re: [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&gt; --- 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,