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Re: [Qemu-devel] [PATCH] io/channel-command: Do not kill the child proce
From: |
Daniel P . Berrangé |
Subject: |
Re: [Qemu-devel] [PATCH] io/channel-command: Do not kill the child process after closing the pipe |
Date: |
Wed, 14 Feb 2018 16:11:08 +0000 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
On Wed, Feb 14, 2018 at 05:09:35PM +0100, Thomas Huth wrote:
> We are currently facing some migration failure on s390x when running
> certain avocado-vt tests, e.g. when running the test
> type_specific.io-github-autotest-qemu.migrate.with_reboot.exec.gzip_exec.
> This test is using 'migrate -d "exec:nc localhost 5200"' for the migration.
> The problem is detected at the receiving side, where the migration stream
> apparently ends too early. However, the cause for the problem is at the
> sending side: After writing the migration stream into the pipe to netcat,
> the source QEMU calls qio_channel_command_close() which closes the pipe
> and immediately (!) kills the child process afterwards (via the function
> qio_channel_command_abort()). So if the sending netcat did not read the
> final bytes from the pipe yet, or if it did not manage to send out all
> its buffers yet, it is killed before the whole migration stream is passed
> to the destination side.
>
> QEMU can not know how much time is required by the child process to send
> over all migration data, so we should not kill it, neither directly nor
> after a delay. Let's simply wait for the child process to exit gracefully
> instead (this was also the behaviour of pclose() that was used in "exec:"
> migration before the QIOChannel rework).
>
> Signed-off-by: Thomas Huth <address@hidden>
> ---
> io/channel-command.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/io/channel-command.c b/io/channel-command.c
> index 319c5ed..3e7eb17 100644
> --- a/io/channel-command.c
> +++ b/io/channel-command.c
> @@ -301,6 +301,9 @@ static int qio_channel_command_close(QIOChannel *ioc,
> {
> QIOChannelCommand *cioc = QIO_CHANNEL_COMMAND(ioc);
> int rv = 0;
> +#ifndef WIN32
> + pid_t wp;
> +#endif
>
> /* We close FDs before killing, because that
> * gives a better chance of clean shutdown
> @@ -315,11 +318,18 @@ static int qio_channel_command_close(QIOChannel *ioc,
> rv = -1;
> }
> cioc->writefd = cioc->readfd = -1;
> +
> #ifndef WIN32
> - if (qio_channel_command_abort(cioc, errp) < 0) {
> + do {
> + wp = waitpid(cioc->pid, NULL, 0);
> + } while (wp == (pid_t)-1 && errno == EINTR);
> + if (wp == (pid_t)-1) {
> + error_setg_errno(errp, errno, "Failed to wait for pid %llu",
> + (unsigned long long)cioc->pid);
> return -1;
> }
> #endif
> +
> if (rv < 0) {
> error_setg_errno(errp, errno, "%s",
> "Unable to close command");
Reviewed-by: Daniel P. Berrangé <address@hidden>
I'll queue this as i had a PR pending...
Regards,
Daniel
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