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([2a01:e0a:280:24f0:576b:abc6:6396:ed4a]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e2a996da2sm74488115e9.5.2025.09.25.00.11.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 25 Sep 2025 00:11:34 -0700 (PDT) Message-ID: <6d5b95e4-1d50-4b70-8d40-9031f3735d56@redhat.com> Date: Thu, 25 Sep 2025 09:11:33 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V4 5/8] migration: cpr-exec save and load To: Steven Sistare , qemu-devel@nongnu.org Cc: Fabiano Rosas , Peter Xu , Markus Armbruster , Paolo Bonzini , Eric Blake , "Dr. David Alan Gilbert" , Alex Williamson References: <1758548985-354793-1-git-send-email-steven.sistare@oracle.com> <1758548985-354793-6-git-send-email-steven.sistare@oracle.com> <15399e70-fa4b-4792-9881-9dec59f0c832@redhat.com> From: =?UTF-8?Q?C=C3=A9dric_Le_Goater?= Content-Language: en-US, fr Autocrypt: addr=clg@redhat.com; keydata= xsFNBFu8o3UBEADP+oJVJaWm5vzZa/iLgpBAuzxSmNYhURZH+guITvSySk30YWfLYGBWQgeo 8NzNXBY3cH7JX3/a0jzmhDc0U61qFxVgrPqs1PQOjp7yRSFuDAnjtRqNvWkvlnRWLFq4+U5t yzYe4SFMjFb6Oc0xkQmaK2flmiJNnnxPttYwKBPd98WfXMmjwAv7QfwW+OL3VlTPADgzkcqj 53bfZ4VblAQrq6Ctbtu7JuUGAxSIL3XqeQlAwwLTfFGrmpY7MroE7n9Rl+hy/kuIrb/TO8n0 ZxYXvvhT7OmRKvbYuc5Jze6o7op/bJHlufY+AquYQ4dPxjPPVUT/DLiUYJ3oVBWFYNbzfOrV RxEwNuRbycttMiZWxgflsQoHF06q/2l4ttS3zsV4TDZudMq0TbCH/uJFPFsbHUN91qwwaN/+ gy1j7o6aWMz+Ib3O9dK2M/j/O/Ube95mdCqN4N/uSnDlca3YDEWrV9jO1mUS/ndOkjxa34ia 70FjwiSQAsyIwqbRO3CGmiOJqDa9qNvd2TJgAaS2WCw/TlBALjVQ7AyoPEoBPj31K74Wc4GS Rm+FSch32ei61yFu6ACdZ12i5Edt+To+hkElzjt6db/UgRUeKfzlMB7PodK7o8NBD8outJGS tsL2GRX24QvvBuusJdMiLGpNz3uqyqwzC5w0Fd34E6G94806fwARAQABzSJDw6lkcmljIExl IEdvYXRlciA8Y2xnQHJlZGhhdC5jb20+wsGRBBMBCAA7FiEEoPZlSPBIlev+awtgUaNDx8/7 7KEFAmTLlVECGwMFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4AACgkQUaNDx8/77KG0eg// S0zIzTcxkrwJ/9XgdcvVTnXLVF9V4/tZPfB7sCp8rpDCEseU6O0TkOVFoGWM39sEMiQBSvyY lHrP7p7E/JYQNNLh441MfaX8RJ5Ul3btluLapm8oHp/vbHKV2IhLcpNCfAqaQKdfk8yazYhh EdxTBlzxPcu+78uE5fF4wusmtutK0JG0sAgq0mHFZX7qKG6LIbdLdaQalZ8CCFMKUhLptW71 xe+aNrn7hScBoOj2kTDRgf9CE7svmjGToJzUxgeh9mIkxAxTu7XU+8lmL28j2L5uNuDOq9vl hM30OT+pfHmyPLtLK8+GXfFDxjea5hZLF+2yolE/ATQFt9AmOmXC+YayrcO2ZvdnKExZS1o8 VUKpZgRnkwMUUReaF/mTauRQGLuS4lDcI4DrARPyLGNbvYlpmJWnGRWCDguQ/LBPpbG7djoy k3NlvoeA757c4DgCzggViqLm0Bae320qEc6z9o0X0ePqSU2f7vcuWN49Uhox5kM5L86DzjEQ RHXndoJkeL8LmHx8DM+kx4aZt0zVfCHwmKTkSTQoAQakLpLte7tWXIio9ZKhUGPv/eHxXEoS 0rOOAZ6np1U/xNR82QbF9qr9TrTVI3GtVe7Vxmff+qoSAxJiZQCo5kt0YlWwti2fFI4xvkOi V7lyhOA3+/3oRKpZYQ86Frlo61HU3r6d9wzOwU0EW7yjdQEQALyDNNMw/08/fsyWEWjfqVhW pOOrX2h+z4q0lOHkjxi/FRIRLfXeZjFfNQNLSoL8j1y2rQOs1j1g+NV3K5hrZYYcMs0xhmrZ KXAHjjDx7FW3sG3jcGjFW5Xk4olTrZwFsZVUcP8XZlArLmkAX3UyrrXEWPSBJCXxDIW1hzwp bV/nVbo/K9XBptT/wPd+RPiOTIIRptjypGY+S23HYBDND3mtfTz/uY0Jytaio9GETj+fFis6 TxFjjbZNUxKpwftu/4RimZ7qL+uM1rG1lLWc9SPtFxRQ8uLvLOUFB1AqHixBcx7LIXSKZEFU CSLB2AE4wXQkJbApye48qnZ09zc929df5gU6hjgqV9Gk1rIfHxvTsYltA1jWalySEScmr0iS YBZjw8Nbd7SxeomAxzBv2l1Fk8fPzR7M616dtb3Z3HLjyvwAwxtfGD7VnvINPbzyibbe9c6g LxYCr23c2Ry0UfFXh6UKD83d5ybqnXrEJ5n/t1+TLGCYGzF2erVYGkQrReJe8Mld3iGVldB7 JhuAU1+d88NS3aBpNF6TbGXqlXGF6Yua6n1cOY2Yb4lO/mDKgjXd3aviqlwVlodC8AwI0Sdu jWryzL5/AGEU2sIDQCHuv1QgzmKwhE58d475KdVX/3Vt5I9kTXpvEpfW18TjlFkdHGESM/Jx IqVsqvhAJkalABEBAAHCwV8EGAECAAkFAlu8o3UCGwwACgkQUaNDx8/77KEhwg//WqVopd5k 8hQb9VVdk6RQOCTfo6wHhEqgjbXQGlaxKHoXywEQBi8eULbeMQf5l4+tHJWBxswQ93IHBQjK yKyNr4FXseUI5O20XVNYDJZUrhA4yn0e/Af0IX25d94HXQ5sMTWr1qlSK6Zu79lbH3R57w9j hQm9emQEp785ui3A5U2Lqp6nWYWXz0eUZ0Tad2zC71Gg9VazU9MXyWn749s0nXbVLcLS0yop s302Gf3ZmtgfXTX/W+M25hiVRRKCH88yr6it+OMJBUndQVAA/fE9hYom6t/zqA248j0QAV/p LHH3hSirE1mv+7jpQnhMvatrwUpeXrOiEw1nHzWCqOJUZ4SY+HmGFW0YirWV2mYKoaGO2YBU wYF7O9TI3GEEgRMBIRT98fHa0NPwtlTktVISl73LpgVscdW8yg9Gc82oe8FzU1uHjU8b10lU XOMHpqDDEV9//r4ZhkKZ9C4O+YZcTFu+mvAY3GlqivBNkmYsHYSlFsbxc37E1HpTEaSWsGfA HQoPn9qrDJgsgcbBVc1gkUT6hnxShKPp4PlsZVMNjvPAnr5TEBgHkk54HQRhhwcYv1T2QumQ izDiU6iOrUzBThaMhZO3i927SG2DwWDVzZltKrCMD1aMPvb3NU8FOYRhNmIFR3fcalYr+9gD uVKe8BVz4atMOoktmt0GWTOC8P4= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=clg@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.444, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 9/24/25 20:16, Steven Sistare wrote: > On 9/22/2025 12:00 PM, Cédric Le Goater wrote: >> On 9/22/25 15:49, Steve Sistare wrote: >>> To preserve CPR state across exec, create a QEMUFile based on a memfd, and >>> keep the memfd open across exec.  Save the value of the memfd in an >>> environment variable so post-exec QEMU can find it. >> >> Couldn't we preserve some memory to hand off to QEMU ? Like firmwares >> An environment variable is a limited method. > > There is no upside in making this more complicated.  We only need to > pass one tidbit of information -- the file descriptor number of the memfd > that contains all other information. Please adjust the build for windows, memfd is Linux only. >> Thanks, >> >> C. >> >> That's a short term hack right ? it's not even documented. > > It is an implementation detail, known only to the matched saving > and loading functions inside qemu.  No one else needs to know, so > no documentation. ok. Fair enough. Thanks, C. > > - Steve > >> I am sure >> you something else in mind. >> >>> These new functions are called in a subsequent patch. >>> >>> Signed-off-by: Steve Sistare >>> --- >>>   include/migration/cpr.h |  5 +++ >>>   migration/cpr-exec.c    | 94 +++++++++++++++++++++++++++++++++++++++++++++++++ >>>   migration/meson.build   |  1 + >>>   3 files changed, 100 insertions(+) >>>   create mode 100644 migration/cpr-exec.c >>> >>> diff --git a/include/migration/cpr.h b/include/migration/cpr.h >>> index 2b074d7..b84389f 100644 >>> --- a/include/migration/cpr.h >>> +++ b/include/migration/cpr.h >>> @@ -53,4 +53,9 @@ int cpr_get_fd_param(const char *name, const char *fdname, int index, >>>   QEMUFile *cpr_transfer_output(MigrationChannel *channel, Error **errp); >>>   QEMUFile *cpr_transfer_input(MigrationChannel *channel, Error **errp); >>> +QEMUFile *cpr_exec_output(Error **errp); >>> +QEMUFile *cpr_exec_input(Error **errp); >>> +void cpr_exec_persist_state(QEMUFile *f); >>> +bool cpr_exec_has_state(void); >>> +void cpr_exec_unpersist_state(void); >>>   #endif >>> diff --git a/migration/cpr-exec.c b/migration/cpr-exec.c >>> new file mode 100644 >>> index 0000000..2c32e9c >>> --- /dev/null >>> +++ b/migration/cpr-exec.c >>> @@ -0,0 +1,94 @@ >>> +/* >>> + * Copyright (c) 2021-2025 Oracle and/or its affiliates. >>> + * >>> + * SPDX-License-Identifier: GPL-2.0-or-later >>> + */ >>> + >>> +#include "qemu/osdep.h" >>> +#include "qemu/cutils.h" >>> +#include "qemu/memfd.h" >>> +#include "qapi/error.h" >>> +#include "io/channel-file.h" >>> +#include "io/channel-socket.h" >>> +#include "migration/cpr.h" >>> +#include "migration/qemu-file.h" >>> +#include "migration/misc.h" >>> +#include "migration/vmstate.h" >>> +#include "system/runstate.h" >>> + >>> +#define CPR_EXEC_STATE_NAME "QEMU_CPR_EXEC_STATE" >>> + >>> +static QEMUFile *qemu_file_new_fd_input(int fd, const char *name) >>> +{ >>> +    g_autoptr(QIOChannelFile) fioc = qio_channel_file_new_fd(fd); >>> +    QIOChannel *ioc = QIO_CHANNEL(fioc); >>> +    qio_channel_set_name(ioc, name); >>> +    return qemu_file_new_input(ioc); >>> +} >>> + >>> +static QEMUFile *qemu_file_new_fd_output(int fd, const char *name) >>> +{ >>> +    g_autoptr(QIOChannelFile) fioc = qio_channel_file_new_fd(fd); >>> +    QIOChannel *ioc = QIO_CHANNEL(fioc); >>> +    qio_channel_set_name(ioc, name); >>> +    return qemu_file_new_output(ioc); >>> +} >>> + >>> +void cpr_exec_persist_state(QEMUFile *f) >>> +{ >>> +    QIOChannelFile *fioc = QIO_CHANNEL_FILE(qemu_file_get_ioc(f)); >>> +    int mfd = dup(fioc->fd); >>> +    char val[16]; >>> + >>> +    /* Remember mfd in environment for post-exec load */ >>> +    qemu_clear_cloexec(mfd); >>> +    snprintf(val, sizeof(val), "%d", mfd); >>> +    g_setenv(CPR_EXEC_STATE_NAME, val, 1); >>> +} >>> + >>> +static int cpr_exec_find_state(void) >>> +{ >>> +    const char *val = g_getenv(CPR_EXEC_STATE_NAME); >>> +    int mfd; >>> + >>> +    assert(val); >>> +    g_unsetenv(CPR_EXEC_STATE_NAME); >>> +    assert(!qemu_strtoi(val, NULL, 10, &mfd)); >>> +    return mfd; >>> +} >>> + >>> +bool cpr_exec_has_state(void) >>> +{ >>> +    return g_getenv(CPR_EXEC_STATE_NAME) != NULL; >>> +} >>> + >>> +void cpr_exec_unpersist_state(void) >>> +{ >>> +    int mfd; >>> +    const char *val = g_getenv(CPR_EXEC_STATE_NAME); >>> + >>> +    g_unsetenv(CPR_EXEC_STATE_NAME); >>> +    assert(val); >>> +    assert(!qemu_strtoi(val, NULL, 10, &mfd)); >>> +    close(mfd); >>> +} >>> + >>> +QEMUFile *cpr_exec_output(Error **errp) >>> +{ >>> +    int mfd = memfd_create(CPR_EXEC_STATE_NAME, 0); >> >> The build should be adjusted for Linux only. >> >> Thanks, >> >> C. >> >> >> >>> + >>> +    if (mfd < 0) { >>> +        error_setg_errno(errp, errno, "memfd_create failed"); >>> +        return NULL; >>> +    } >>> + >>> +    return qemu_file_new_fd_output(mfd, CPR_EXEC_STATE_NAME); >>> +} >>> + >>> +QEMUFile *cpr_exec_input(Error **errp) >>> +{ >>> +    int mfd = cpr_exec_find_state(); >>> + >>> +    lseek(mfd, 0, SEEK_SET); >>> +    return qemu_file_new_fd_input(mfd, CPR_EXEC_STATE_NAME); >>> +} >>> diff --git a/migration/meson.build b/migration/meson.build >>> index 0f71544..16909d5 100644 >>> --- a/migration/meson.build >>> +++ b/migration/meson.build >>> @@ -16,6 +16,7 @@ system_ss.add(files( >>>     'channel-block.c', >>>     'cpr.c', >>>     'cpr-transfer.c', >>> +  'cpr-exec.c', >>>     'cpu-throttle.c', >>>     'dirtyrate.c', >>>     'exec.c', >> >