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Thu, 26 Mar 2026 12:25:51 -0700 (PDT) X-Received: by 2002:a05:620a:1a01:b0:8cf:ba85:e9f6 with SMTP id af79cd13be357-8d000f1733dmr1262122085a.2.1774553150315; Thu, 26 Mar 2026 12:25:50 -0700 (PDT) Received: from x1.local ([142.189.10.167]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8d00e3bec81sm335735885a.11.2026.03.26.12.25.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Mar 2026 12:25:49 -0700 (PDT) Date: Thu, 26 Mar 2026 15:25:47 -0400 From: Peter Xu To: Fabiano Rosas Cc: qemu-devel@nongnu.org, Alexander Mikhalitsyn , Juraj Marcin Subject: Re: [PATCH RFC 07/10] vmstate: Allow vmstate_info_nullptr to emit non-NULL markers Message-ID: References: <20260317232332.15209-1-peterx@redhat.com> <20260317232332.15209-8-peterx@redhat.com> <87cy0z35ub.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <87cy0z35ub.fsf@suse.de> 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: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H2=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_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: qemu development 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 Thu, Mar 19, 2026 at 05:46:36PM -0300, Fabiano Rosas wrote: > Peter Xu writes: > > > 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. > > > > No functional change intended yet. > > > > Signed-off-by: Peter Xu > > --- > > include/migration/vmstate.h | 9 +++++++-- > > migration/vmstate-types.c | 34 ++++++++++++++++------------------ > > migration/vmstate.c | 29 ++++++++++++++--------------- > > 3 files changed, 37 insertions(+), 35 deletions(-) > > > > diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h > > index 092e8f7e9a..2e51b5ea04 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; > > > > -/** 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; > > > > extern const VMStateInfo vmstate_info_cpudouble; > > > > 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 = { > > .save = save_fd, > > }; > > > > -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) > > > > { > > - if (qemu_get_byte(f) == VMS_MARKER_PTR_NULL) { > > + int byte = qemu_get_byte(f); > > + > > + if (byte == VMS_MARKER_PTR_NULL || byte == VMS_MARKER_PTR_VALID) { > > + /* TODO: process PTR_VALID case */ > > return true; > > } > > > > - error_setg(errp, "vmstate: load_nullptr expected VMS_NULLPTR_MARKER"); > > + error_setg(errp, "%s: unexpected ptr marker: %d", __func__, byte); > > return false; > > } > > > > -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) > > > > { > > - if (pv == NULL) { > > - qemu_put_byte(f, VMS_MARKER_PTR_NULL); > > - return true; > > - } > > - > > - error_setg(errp, "vmstate: save_nullptr must be called with pv == NULL"); > > - return false; > > + qemu_put_byte(f, pv ? VMS_MARKER_PTR_VALID : VMS_MARKER_PTR_NULL); > > + return true; > > } > > > > -const VMStateInfo vmstate_info_nullptr = { > > - .name = "nullptr", > > - .load = load_nullptr, > > - .save = save_nullptr, > > +const VMStateInfo vmstate_info_ptr_marker = { > > + .name = "ptr-marker", > > + .load = load_ptr_marker, > > + .save = save_ptr_marker, > > }; > > > > /* 64 bit unsigned int. See that the received value is the same than the one > > diff --git a/migration/vmstate.c b/migration/vmstate.c > > index 5a6b352764..a3a5f25946 100644 > > --- a/migration/vmstate.c > > +++ b/migration/vmstate.c > > @@ -55,12 +55,12 @@ vmstate_field_exists(const VMStateDescription *vmsd, const VMStateField *field, > > } > > > > /* > > - * 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 = g_new0(VMStateField, 1); > > > > @@ -76,7 +76,7 @@ vmsd_create_fake_nullptr_field(const VMStateField *field) > > > > /* See vmstate_info_nullptr - use 1 byte to represent nullptr */ > > This comment needs updating. Fixed. > > > fake->size = 1; > > - fake->info = &vmstate_info_nullptr; > > + fake->info = &vmstate_info_ptr_marker; > > fake->flags = VMS_SINGLE; > > > > /* All the rest fields shouldn't matter.. */ > > @@ -278,7 +278,7 @@ bool vmstate_load_vmsd(QEMUFile *f, const VMStateDescription *vmsd, > > * an array of pointers), use null placeholder and do > > * not follow. > > */ > > - inner_field = vmsd_create_fake_nullptr_field(field); > > + inner_field = vmsd_create_ptr_marker_field(field); > > } else { > > inner_field = field; > > } > > @@ -567,7 +567,7 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VMStateDescription *vmsd, > > int i, n_elems = vmstate_n_elems(opaque, field); > > int size = vmstate_size(opaque, field); > > JSONWriter *vmdesc_loop = vmdesc; > > - bool is_prev_null = false; > > + bool use_marker_field_prev = false; > > The logic below won't handle valid pointer as well, will it? We could > leave the is_null/is_prev_null terminology because it's way more > descriptive. Right? We're adding the marker here because we're > compressing and know the field is null. I recovered the old bool for better readability. One other note is I'll squash below analyze-migration.py change into this patch when repost, let me know if there's early comments: ===8<=== >From 82ac38a85ecd990a1aaa7b45b172e71f0d5b84da Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Thu, 26 Mar 2026 14:57:56 -0400 Subject: [PATCH] scripts/analyze-migration.py: Support new ptr-marker field Signed-off-by: Peter Xu --- scripts/analyze-migration.py | 22 ++++++++++++---------- 1 file changed, 12 insertions(+), 10 deletions(-) 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 = '