Commit dd272c8c87 for qemu.org

commit dd272c8c87f165d41c945946242c5c8619e7122f
Author: Denis V. Lunev <den@openvz.org>
Date:   Fri Jul 31 17:50:01 2026 +0200

    qapi/dump: add allowed-by-guest feature to win-dmp

    Commit 1c0e259c5a35 ("dump: make win_dump_available() check vmcoreinfo
    for a Windows dump header") changed two things in a way that is visible
    to QMP clients but not to introspection:
    query-dump-guest-memory-capability now lists win-dmp only for a guest
    that has published a Windows dump header through the vmcoreinfo device,
    and dump-guest-memory, which shares win_dump_available(), rejects the
    format otherwise. Before that, both accepted win-dmp on any x86
    machine.

    A client that wants to select win-dmp automatically therefore cannot
    trust the capability query on its own: on an older QEMU it reports
    win-dmp for every x86 guest, Linux ones included, where the resulting
    dump is useless. libvirt ran into exactly this while picking a format
    for on_crash and watchdog triggered dumps, and has no way to tell the
    two behaviours apart.

    Add an 'allowed-by-guest' feature to the win-dmp member of
    DumpGuestMemoryFormat so the fixed behaviour becomes discoverable.
    DumpGuestMemoryFormat is reachable from both
    query-dump-guest-memory-capability's return type and
    dump-guest-memory's arguments, so a single flag covers both halves of
    the change. Where the feature is absent, a reported win-dmp says
    nothing about the guest, and a client that needs the dump to be
    loadable afterwards should fall back to elf.

    CC: Eric Blake <eblake@redhat.com>
    CC: Markus Armbruster <armbru@redhat.com>
    CC: "Marc-André Lureau" <marcandre.lureau@redhat.com>
    Suggested-by: Daniel P. Berrangé <berrange@redhat.com>
    Signed-off-by: Denis V. Lunev <den@openvz.org>
    Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
    Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
    Message-ID: <20260731155001.1204103-1-den@openvz.org>

diff --git a/qapi/dump.json b/qapi/dump.json
index 726b520870..690f3963fe 100644
--- a/qapi/dump.json
+++ b/qapi/dump.json
@@ -38,6 +38,13 @@
 # @win-dmp: Windows full crashdump format, can be used instead of ELF
 #     converting (since 2.13)
 #
+# Features:
+#
+# @allowed-by-guest: If present, @win-dmp is listed by
+#     `query-dump-guest-memory-capability`, and accepted by
+#     `dump-guest-memory`, only when the guest has published a Windows
+#     dump header through the vmcoreinfo device (since 11.1)
+#
 # Since: 2.0
 ##
 { 'enum': 'DumpGuestMemoryFormat',
@@ -45,7 +52,7 @@
       'elf',
       'kdump-zlib', 'kdump-lzo', 'kdump-snappy',
       'kdump-raw-zlib', 'kdump-raw-lzo', 'kdump-raw-snappy',
-      'win-dmp' ] }
+      { 'name': 'win-dmp', 'features': ['allowed-by-guest'] } ] }

 ##
 # @dump-guest-memory: