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Wed, 01 Apr 2026 13:28:56 -0700 (PDT) X-Received: by 2002:a05:620a:404c:b0:8cb:9975:cba8 with SMTP id af79cd13be357-8d1b5c5782cmr818797985a.62.1775075335852; Wed, 01 Apr 2026 13:28:55 -0700 (PDT) From: Peter Xu To: qemu-devel@nongnu.org Cc: Juraj Marcin , Alexander Mikhalitsyn , Fabiano Rosas , Peter Xu , Alexander Mikhalitsyn Subject: [PATCH 07/11] vmstate: Allow vmstate_info_nullptr to emit non-NULL markers Date: Wed, 1 Apr 2026 16:28:40 -0400 Message-ID: <20260401202844.673494-8-peterx@redhat.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20260401202844.673494-1-peterx@redhat.com> References: <20260401202844.673494-1-peterx@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.129.124; envelope-from=peterx@redhat.com; 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, 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_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=1, RCVD_IN_VALIDITY_RPBL_BLOCKED=1, 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: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1775075422305158500 Content-Type: text/plain; charset="utf-8" We used to have one vmstate called "nullptr" which is only used to generate one-byte hint to say one pointer is NULL. Let's extend its use so that it will generate another byte to say the pointer is non-NULL. With that, the name of the info struct (or functions) do not apply anymore. Update correspondingly. Update analyze-migration.py to work with the new layout. No functional change intended yet. Reviewed-by: Fabiano Rosas Reviewed-by: Alexander Mikhalitsyn Signed-off-by: Peter Xu --- include/migration/vmstate.h | 9 +++++++-- migration/vmstate-types.c | 34 ++++++++++++++++------------------ migration/vmstate.c | 25 +++++++++++++------------ scripts/analyze-migration.py | 22 ++++++++++++---------- 4 files changed, 48 insertions(+), 42 deletions(-) diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h index 7396e38531..492069b8d2 100644 --- a/include/migration/vmstate.h +++ b/include/migration/vmstate.h @@ -282,9 +282,14 @@ extern const VMStateInfo vmstate_info_uint32; extern const VMStateInfo vmstate_info_uint64; extern const VMStateInfo vmstate_info_fd; =20 -/** Put this in the stream when migrating a null pointer.*/ +/* + * Put this in the stream when migrating a pointer to reflect either a NULL + * or valid pointer. + */ #define VMS_MARKER_PTR_NULL (0x30U) /* '0' */ -extern const VMStateInfo vmstate_info_nullptr; +#define VMS_MARKER_PTR_VALID (0x31U) /* '1' */ + +extern const VMStateInfo vmstate_info_ptr_marker; =20 extern const VMStateInfo vmstate_info_cpudouble; =20 diff --git a/migration/vmstate-types.c b/migration/vmstate-types.c index 7622cf8f01..b31689fc3c 100644 --- a/migration/vmstate-types.c +++ b/migration/vmstate-types.c @@ -359,36 +359,34 @@ const VMStateInfo vmstate_info_fd =3D { .save =3D save_fd, }; =20 -static bool load_nullptr(QEMUFile *f, void *pv, size_t size, - const VMStateField *field, Error **errp) +static bool load_ptr_marker(QEMUFile *f, void *pv, size_t size, + const VMStateField *field, Error **errp) =20 { - if (qemu_get_byte(f) =3D=3D VMS_MARKER_PTR_NULL) { + int byte =3D qemu_get_byte(f); + + if (byte =3D=3D VMS_MARKER_PTR_NULL || byte =3D=3D VMS_MARKER_PTR_VALI= D) { + /* TODO: process PTR_VALID case */ return true; } =20 - error_setg(errp, "vmstate: load_nullptr expected VMS_NULLPTR_MARKER"); + error_setg(errp, "%s: unexpected ptr marker: %d", __func__, byte); return false; } =20 -static bool save_nullptr(QEMUFile *f, void *pv, size_t size, - const VMStateField *field, JSONWriter *vmdesc, - Error **errp) +static bool save_ptr_marker(QEMUFile *f, void *pv, size_t size, + const VMStateField *field, JSONWriter *vmdesc, + Error **errp) =20 { - if (pv =3D=3D NULL) { - qemu_put_byte(f, VMS_MARKER_PTR_NULL); - return true; - } - - error_setg(errp, "vmstate: save_nullptr must be called with pv =3D=3D = NULL"); - return false; + qemu_put_byte(f, pv ? VMS_MARKER_PTR_VALID : VMS_MARKER_PTR_NULL); + return true; } =20 -const VMStateInfo vmstate_info_nullptr =3D { - .name =3D "nullptr", - .load =3D load_nullptr, - .save =3D save_nullptr, +const VMStateInfo vmstate_info_ptr_marker =3D { + .name =3D "ptr-marker", + .load =3D load_ptr_marker, + .save =3D save_ptr_marker, }; =20 /* 64 bit unsigned int. See that the received value is the same than the o= ne diff --git a/migration/vmstate.c b/migration/vmstate.c index b274204e66..b333aa1744 100644 --- a/migration/vmstate.c +++ b/migration/vmstate.c @@ -55,12 +55,12 @@ vmstate_field_exists(const VMStateDescription *vmsd, co= nst VMStateField *field, } =20 /* - * Create a fake nullptr field when there's a NULL pointer detected in the + * Create a ptr marker field when there's a NULL pointer detected in the * array of a VMS_ARRAY_OF_POINTER VMSD field. It's needed because we * can't dereference the NULL pointer. */ static const VMStateField * -vmsd_create_fake_nullptr_field(const VMStateField *field) +vmsd_create_ptr_marker_field(const VMStateField *field) { VMStateField *fake =3D g_new0(VMStateField, 1); =20 @@ -71,12 +71,12 @@ vmsd_create_fake_nullptr_field(const VMStateField *fiel= d) fake->name =3D field->name; fake->version_id =3D field->version_id; =20 - /* Do not need "field_exists" check as it always exists (which is null= ) */ + /* Do not need "field_exists" check as it always exists */ fake->field_exists =3D NULL; =20 - /* See vmstate_info_nullptr - use 1 byte to represent nullptr */ + /* See vmstate_info_ptr_marker - use 1 byte to represent ptr status */ fake->size =3D 1; - fake->info =3D &vmstate_info_nullptr; + fake->info =3D &vmstate_info_ptr_marker; fake->flags =3D VMS_SINGLE; =20 /* All the rest fields shouldn't matter.. */ @@ -278,7 +278,7 @@ bool vmstate_load_vmsd(QEMUFile *f, const VMStateDescri= ption *vmsd, * an array of pointers), use null placeholder and do * not follow. */ - inner_field =3D vmsd_create_fake_nullptr_field(field); + inner_field =3D vmsd_create_ptr_marker_field(field); } else { inner_field =3D field; } @@ -583,26 +583,27 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VM= StateDescription *vmsd, for (i =3D 0; i < n_elems; i++) { void *curr_elem =3D first_elem + size * i; const VMStateField *inner_field; - bool is_null; /* maximum number of elements to compress in the JSON blob= */ int max_elems =3D vmsd_can_compress(field) ? (n_elems - i)= : 1; + bool use_marker_field, is_null; =20 if (field->flags & VMS_ARRAY_OF_POINTER) { assert(curr_elem); curr_elem =3D *(void **)curr_elem; } =20 - if (!curr_elem && size) { + is_null =3D !curr_elem && size; + use_marker_field =3D is_null; + + if (use_marker_field) { /* * If null pointer found (which should only happen in * an array of pointers), use null placeholder and do * not follow. */ - inner_field =3D vmsd_create_fake_nullptr_field(field); - is_null =3D true; + inner_field =3D vmsd_create_ptr_marker_field(field); } else { inner_field =3D field; - is_null =3D false; } =20 /* @@ -638,7 +639,7 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VMSt= ateDescription *vmsd, i, max_elems, errp); =20 /* If we used a fake temp field.. free it now */ - if (is_null) { + if (use_marker_field) { g_clear_pointer((gpointer *)&inner_field, g_free); } =20 diff --git a/scripts/analyze-migration.py b/scripts/analyze-migration.py index e81deab8f9..1771ff781b 100755 --- a/scripts/analyze-migration.py +++ b/scripts/analyze-migration.py @@ -469,26 +469,26 @@ def __init__(self, desc, file): super(VMSDFieldIntLE, self).__init__(desc, file) self.dtype =3D '