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Wed, 25 Mar 2026 10:07:42 -0700 (PDT) X-Received: by 2002:a05:622a:5b95:b0:509:2448:41a with SMTP id d75a77b69052e-50b80de0052mr59921411cf.42.1774458462154; Wed, 25 Mar 2026 10:07:42 -0700 (PDT) Received: from x1.local ([142.189.10.167]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-50b9239fd9bsm2893441cf.22.2026.03.25.10.07.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Mar 2026 10:07:41 -0700 (PDT) Date: Wed, 25 Mar 2026 13:07:40 -0400 From: Peter Xu To: Fabiano Rosas Cc: qemu-devel@nongnu.org, Alexander Mikhalitsyn , Juraj Marcin Subject: Re: [RFC PATCH v1 05/17] vmstate: Remove vmdesc_loop Message-ID: References: <20260324194333.30004-1-farosas@suse.de> <20260324194333.30004-6-farosas@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260324194333.30004-6-farosas@suse.de> Received-SPF: pass client-ip=170.10.133.124; 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_H5=0.001, RCVD_IN_MSPIKE_WL=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 Tue, Mar 24, 2026 at 04:43:20PM -0300, Fabiano Rosas wrote: > The vmdesc_loop variable is being used as a hacky way of writing the > JSON description only for the first element of a compressed > array. There are also a few implicit uses, such as writing the JSON > for the first non-compressed element after a compressed portion. > > Future work will have trouble with this. Use a simple boolean to be > explicit now. > > Signed-off-by: Fabiano Rosas > --- > migration/vmstate.c | 25 ++++++++++++++----------- > 1 file changed, 14 insertions(+), 11 deletions(-) > > diff --git a/migration/vmstate.c b/migration/vmstate.c > index dec9cf920b..7a12245d36 100644 > --- a/migration/vmstate.c > +++ b/migration/vmstate.c > @@ -622,8 +622,9 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VMStateDescription *vmsd, > void *first_elem = opaque + field->offset; > int i, n_elems = vmstate_n_elems(opaque, field); > int size = vmstate_size(opaque, field); > - JSONWriter *vmdesc_loop = vmdesc; > bool is_null_prev = false; > + bool use_vmdesc = true; > + > /* > * When this is enabled, it means we will always push a ptr > * marker first for each element saying if it's populated. > @@ -673,7 +674,7 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VMStateDescription *vmsd, > is_null != is_null_prev) { > > is_null_prev = is_null; > - vmdesc_loop = vmdesc; > + use_vmdesc = true; > > for (int j = i + 1; j < n_elems; j++) { > void *elem = *(void **)(first_elem + size * j); > @@ -686,8 +687,13 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VMStateDescription *vmsd, > } > } > > + if (use_dynamic_array) { > + use_vmdesc = true; > + } [1] > + > ok = vmstate_save_field_with_vmdesc(f, curr_elem, size, vmsd, > - inner_field, vmdesc_loop, > + inner_field, > + use_vmdesc ? vmdesc : NULL, > i, max_elems, errp); > > /* If we used a fake temp field.. free it now */ > @@ -708,19 +714,16 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VMStateDescription *vmsd, > * NOTE: do not use vmstate_size() here because we want > * to dump the real VMSD object now. > */ > - ok = vmstate_save_field_with_vmdesc(f, curr_elem, > - field->size, vmsd, > - field, vmdesc_loop, > - i, max_elems, errp); > + ok = vmstate_save_field_with_vmdesc( > + f, curr_elem, field->size, vmsd, field, > + use_vmdesc ? vmdesc : NULL, i, max_elems, errp); > + > if (!ok) { > goto out; > } > } > > - /* Compressed arrays only care about the first element */ > - if (vmdesc_loop && vmsd_can_compress(field)) { > - vmdesc_loop = NULL; > - } > + use_vmdesc = false; Hmm... vmsd_can_compress() can return arbitrary things depending on the field itself, now we always do the dedup almost for everything. The patch did add above [1] to make AUTO_ALLOC be ok, by enforce setting TRUE for it for every loop, but what about other cases where vmsd_can_compress() may return false (where the field does not support compression)? > } > } else { > if (field->flags & VMS_MUST_EXIST) { > -- > 2.51.0 > -- Peter Xu