{"id":2218745,"url":"http://patchwork.ozlabs.org/api/1.0/patches/2218745/?format=json","project":{"id":14,"url":"http://patchwork.ozlabs.org/api/1.0/projects/14/?format=json","name":"QEMU Development","link_name":"qemu-devel","list_id":"qemu-devel.nongnu.org","list_email":"qemu-devel@nongnu.org","web_url":"","scm_url":"","webscm_url":""},"msgid":"<20260401202844.673494-5-peterx@redhat.com>","date":"2026-04-01T20:28:37","name":"[04/11] vmstate: Update max_elems early and check field compressable once","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"9d2e2d8f978c730cd92652a0eed658edc0a02cf0","submitter":{"id":67717,"url":"http://patchwork.ozlabs.org/api/1.0/people/67717/?format=json","name":"Peter Xu","email":"peterx@redhat.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/qemu-devel/patch/20260401202844.673494-5-peterx@redhat.com/mbox/","series":[{"id":498385,"url":"http://patchwork.ozlabs.org/api/1.0/series/498385/?format=json","date":"2026-04-01T20:28:34","name":"vmstate: Implement VMS_ARRAY_OF_POINTER_AUTO_ALLOC","version":1,"mbox":"http://patchwork.ozlabs.org/series/498385/mbox/"}],"check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2218745/checks/","tags":{},"headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=BrglIskr;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=google header.b=nVniMVfh;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; 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envelope-from=peterx@redhat.com;\n helo=us-smtp-delivery-124.mimecast.com","X-Spam_score_int":"-6","X-Spam_score":"-0.7","X-Spam_bar":"/","X-Spam_report":"(-0.7 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.54,\n DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1,\n RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01,\n RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=1, RCVD_IN_VALIDITY_RPBL_BLOCKED=1,\n SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no","X-Spam_action":"no action","X-BeenThere":"qemu-devel@nongnu.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"qemu development ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org","Sender":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org"},"content":"QEMU has a trick in vmstate_save_vmsd_v(), where it will try to compress\nmultiple JSON entries into one with a count to avoid duplicated entries.\n\nThat only applies to the cases where vmsd_can_compress() should return\ntrue. For example, vmsd_desc_field_start() later (who will take the\nupdated max_elems as the last parameter) will ignore the value passed in\nwhen vmsd_can_compress() returns false.\n\nDo that check once at the start of loop, and use it to update max_elems, so\nthat max_elems keeps 1 for uncompressable VMSD fields, which is more\nstraightforward.\n\nThis also paves way to make this counter work for ptr marker VMSD fields\ntoo.\n\nNo functional change intended in this patch alone.\n\nReviewed-by: Fabiano Rosas \nReviewed-by: Alexander Mikhalitsyn \nSigned-off-by: Peter Xu \n---\n migration/vmstate.c | 8 +++++---\n 1 file changed, 5 insertions(+), 3 deletions(-)","diff":"diff --git a/migration/vmstate.c b/migration/vmstate.c\nindex e29a8c3f49..05badef42f 100644\n--- a/migration/vmstate.c\n+++ b/migration/vmstate.c\n@@ -556,7 +556,8 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VMStateDescription *vmsd,\n void *curr_elem = first_elem + size * i;\n const VMStateField *inner_field;\n bool is_null;\n- int max_elems = n_elems - i;\n+ /* maximum number of elements to compress in the JSON blob */\n+ int max_elems = vmsd_can_compress(field) ? (n_elems - i) : 1;\n \n old_offset = qemu_file_transferred(f);\n if (field->flags & VMS_ARRAY_OF_POINTER) {\n@@ -587,7 +588,8 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VMStateDescription *vmsd,\n * vs. nullptr). Search ahead for the next null/non-null element\n * and start a new compressed array if found.\n */\n- if (vmdesc && (field->flags & VMS_ARRAY_OF_POINTER) &&\n+ if (vmdesc && max_elems > 1 &&\n+ (field->flags & VMS_ARRAY_OF_POINTER) &&\n is_null != is_prev_null) {\n \n is_prev_null = is_null;\n@@ -626,7 +628,7 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VMStateDescription *vmsd,\n }\n \n /* Compressed arrays only care about the first element */\n- if (vmdesc_loop && vmsd_can_compress(field)) {\n+ if (vmdesc_loop && max_elems > 1) {\n vmdesc_loop = NULL;\n }\n }\n","prefixes":["04/11"]}