On Wed, Oct 17, 2018 at 11:06:43AM +0200, Michal Privoznik wrote:
> 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@xxxxxxxxxx>
> ---
> src/libvirt_private.syms | 1 +
> src/util/virprocess.c | 81 ++++++++++++++++++++++++++++++++++++++++
> src/util/virprocess.h | 16 ++++++++
> 3 files changed, 98 insertions(+)
> +/**
> + * 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.
Instead of;
However, due to possible signal propagation @cb should only call
async signal safe functions.
Use:
All signals will be reset to have their platform default handlers
and unmasked. @cb must only use async signal safe functions. In
particular no mutexes should be used in @cb, unless steps were
taken before forking to guarantee a predictable state. @cb must
not exec any external binaries, instead virCommand/virExec should
be used for that purpose.
> + */
> +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));
It would be desirable to include the exit status value in the message
> + }
> + }
> + }
> +
> + cleanup:
> + VIR_FORCE_CLOSE(errfd[0]);
> + VIR_FORCE_CLOSE(errfd[1]);
> + return ret;
> +}
Regards,
Daniel
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