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[2003:cf:5722:8c00:51af:80c5:4da1:a9bc]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4856ea9c36bsm61977665e9.9.2026.03.17.03.27.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 17 Mar 2026 03:27:11 -0700 (PDT) From: Alexander Mikhalitsyn To: qemu-devel@nongnu.org Cc: Alexander Mikhalitsyn , Peter Xu , Fabiano Rosas , Jesper Devantier , Klaus Jensen , =?UTF-8?q?St=C3=A9phane=20Graber?= , qemu-block@nongnu.org, Stefan Hajnoczi , Hanna Reitz , Paolo Bonzini , Keith Busch , Fam Zheng , =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= , Zhao Liu , Kevin Wolf , Alexander Mikhalitsyn Subject: [PATCH v5 2/8] migration: add VMSTATE_VARRAY_OF_POINTER_TO_STRUCT_UINT{8, 32}_ALLOC Date: Tue, 17 Mar 2026 11:27:02 +0100 Message-ID: <20260317102708.126725-3-alexander@mihalicyn.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260317102708.126725-1-alexander@mihalicyn.com> References: <20260317102708.126725-1-alexander@mihalicyn.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::329; envelope-from=alexander@mihalicyn.com; helo=mail-wm1-x329.google.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, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=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 From: Alexander Mikhalitsyn Add VMSTATE_VARRAY_OF_POINTER_TO_STRUCT_UINT{8, 32}_ALLOC, which helps to save/restore a dynamic array of pointers to structures. Suggested-by: Peter Xu Signed-off-by: Alexander Mikhalitsyn v2: - added VMSTATE_VARRAY_OF_POINTER_TO_STRUCT_UINT8_ALLOC v4: - almost completely reworked, new flag VMS_ARRAY_OF_POINTER_ALLOW_NULL was introduced as suggested by Peter v5: - rebased on top of https://lore.kernel.org/all/20260304212303.667141-1-vsementsov@yandex-team.ru/ --- include/migration/vmstate.h | 77 ++++++++++++++++++++++++++++++- migration/savevm.c | 26 +++++++++++ migration/vmstate-types.c | 91 +++++++++++++++++++++++++++++++++++++ migration/vmstate.c | 54 ++++++++++++++++++---- 4 files changed, 236 insertions(+), 12 deletions(-) diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h index 7ed4a0742b2..0a409700598 100644 --- a/include/migration/vmstate.h +++ b/include/migration/vmstate.h @@ -162,7 +162,19 @@ enum VMStateFlags { VMS_VSTRUCT = 0x8000, /* Marker for end of list */ - VMS_END = 0x10000 + VMS_END = 0x10000, + + /* The field is a (fixed-size or variable-size) array of pointers + * (e.g. struct a { uint8_t **b; }) that can contain NULL values. + * This instructs vmstate engine to: + * - Dereference each array entry before using it. + * - Assume that array is initialized with NULLs on load phase + * - Automatically allocate memory for array entries (with size + * specified in (VMStateField).start) on load phase + * - Produce NULL/not-NULL markers in migration stream + * + * Note: Does not imply VMS_ARRAY_OF_POINTER; it needs to be set explicitly. */ + VMS_ARRAY_OF_POINTER_ALLOW_NULL = 0x20000, }; typedef enum { @@ -194,6 +206,7 @@ struct VMStateField { int version_id; int struct_version_id; bool (*field_exists)(void *opaque, int version_id); + const struct VMStateField *real_field; }; struct VMStateDescription { @@ -268,8 +281,10 @@ extern const VMStateInfo vmstate_info_uint64; extern const VMStateInfo vmstate_info_fd; /** Put this in the stream when migrating a null pointer.*/ -#define VMS_NULLPTR_MARKER (0x30U) /* '0' */ +#define VMS_NULLPTR_MARKER (0x30U) /* '0' */ +#define VMS_NOTNULLPTR_MARKER (0x31U) /* '1' */ extern const VMStateInfo vmstate_info_nullptr; +extern const VMStateInfo vmstate_info_maybeptr; extern const VMStateInfo vmstate_info_cpudouble; @@ -281,6 +296,7 @@ extern const VMStateInfo vmstate_info_bitmap; extern const VMStateInfo vmstate_info_qtailq; extern const VMStateInfo vmstate_info_gtree; extern const VMStateInfo vmstate_info_qlist; +extern const VMStateInfo vmstate_info_ptrs_array_entry; #define type_check_2darray(t1,t2,n,m) ((t1(*)[n][m])0 - (t2*)0) /* @@ -562,6 +578,63 @@ extern const VMStateInfo vmstate_info_qlist; .offset = vmstate_offset_array(_s, _f, _type*, _n), \ } +/* + * For migrating a dynamically allocated uint{8,32}-indexed array + * of pointers to structures (with NULL entries and with auto memory allocation). + * + * _type: type of structure pointed to + * _vmsd: VMSD for structure _type (when VMS_STRUCT is set) + * _info: VMStateInfo for _type (when VMS_STRUCT is not set) + * start: size of (_type) pointed to (for auto memory allocation) + */ +#define VMSTATE_VARRAY_OF_POINTER_TO_STRUCT_UINT8_ALLOC(_field, _state, _field_num, _version, _vmsd, _type) { \ + .name = (stringify(_field)), \ + .version_id = (_version), \ + .num_offset = vmstate_offset_value(_state, _field_num, uint8_t), \ + .vmsd = &(_vmsd), \ + .start = sizeof(_type), \ + .size = sizeof(_type *), \ + .flags = VMS_POINTER|VMS_VARRAY_UINT8|VMS_ARRAY_OF_POINTER| \ + VMS_ARRAY_OF_POINTER_ALLOW_NULL|VMS_STRUCT, \ + .offset = vmstate_offset_pointer(_state, _field, _type *), \ +} + +#define VMSTATE_VARRAY_OF_POINTER_UINT8_ALLOC(_field, _state, _field_num, _version, _info, _type) { \ + .name = (stringify(_field)), \ + .version_id = (_version), \ + .num_offset = vmstate_offset_value(_state, _field_num, uint8_t), \ + .info = &(_info), \ + .start = sizeof(_type), \ + .size = sizeof(_type *), \ + .flags = VMS_POINTER|VMS_VARRAY_UINT8|VMS_ARRAY_OF_POINTER| \ + VMS_ARRAY_OF_POINTER_ALLOW_NULL, \ + .offset = vmstate_offset_pointer(_state, _field, _type *), \ +} + +#define VMSTATE_VARRAY_OF_POINTER_TO_STRUCT_UINT32_ALLOC(_field, _state, _field_num, _version, _vmsd, _type) { \ + .name = (stringify(_field)), \ + .version_id = (_version), \ + .num_offset = vmstate_offset_value(_state, _field_num, uint32_t), \ + .vmsd = &(_vmsd), \ + .start = sizeof(_type), \ + .size = sizeof(_type *), \ + .flags = VMS_POINTER|VMS_VARRAY_UINT32|VMS_ARRAY_OF_POINTER| \ + VMS_ARRAY_OF_POINTER_ALLOW_NULL|VMS_STRUCT, \ + .offset = vmstate_offset_pointer(_state, _field, _type *), \ +} + +#define VMSTATE_VARRAY_OF_POINTER_UINT32_ALLOC(_field, _state, _field_num, _version, _info, _type) { \ + .name = (stringify(_field)), \ + .version_id = (_version), \ + .num_offset = vmstate_offset_value(_state, _field_num, uint32_t), \ + .info = &(_info), \ + .start = sizeof(_type), \ + .size = sizeof(_type *), \ + .flags = VMS_POINTER|VMS_VARRAY_UINT32|VMS_ARRAY_OF_POINTER| \ + VMS_ARRAY_OF_POINTER_ALLOW_NULL, \ + .offset = vmstate_offset_pointer(_state, _field, _type *), \ +} + #define VMSTATE_VARRAY_OF_POINTER_UINT32(_field, _state, _field_num, _version, _info, _type) { \ .name = (stringify(_field)), \ .version_id = (_version), \ diff --git a/migration/savevm.c b/migration/savevm.c index 8115203b518..882c882f684 100644 --- a/migration/savevm.c +++ b/migration/savevm.c @@ -868,6 +868,32 @@ static void vmstate_check(const VMStateDescription *vmsd) if (field) { while (field->name) { + /* + * VMS_ARRAY_OF_POINTER must be used only together + * with one of VMS_(V)ARRAY* flags. + */ + assert(!(field->flags & VMS_ARRAY_OF_POINTER) || + ((field->flags & (VMS_ARRAY | VMS_VARRAY_INT32 | + VMS_VARRAY_UINT16 | VMS_VARRAY_UINT8 | VMS_VARRAY_UINT32)))); + + /* + * When VMS_ARRAY_OF_POINTER_ALLOW_NULL is used, we must: + * 1. have VMS_ARRAY_OF_POINTER set too; + * 2. have ->start field set and it should tell us a size + * of memory chunk we should allocate for every array member. + */ + assert(!(field->flags & VMS_ARRAY_OF_POINTER_ALLOW_NULL) || + (field->flags & VMS_ARRAY_OF_POINTER)); + assert(!(field->flags & VMS_ARRAY_OF_POINTER_ALLOW_NULL) || + field->start); + + /* + * (VMStateField).real_field is only for internal purposes + * and should never be used by any user-defined VMStateField. + * Currently, it is only used by vmsd_create_fake_nullptr_field(). + */ + assert(!field->real_field); + if (field->flags & (VMS_STRUCT | VMS_VSTRUCT)) { /* Recurse to sub structures */ vmstate_check(field->vmsd); diff --git a/migration/vmstate-types.c b/migration/vmstate-types.c index 23f34336964..a55f4d51f4b 100644 --- a/migration/vmstate-types.c +++ b/migration/vmstate-types.c @@ -391,6 +391,97 @@ const VMStateInfo vmstate_info_nullptr = { .save = save_nullptr, }; +static bool load_maybeptr(QEMUFile *f, void *ppv, size_t unused_size, + const VMStateField *field, Error **errp) +{ + bool ok = false; + const VMStateField *real_field = field->real_field; + /* size of structure pointed to by elements of array */ + size_t size = real_field->start; + int marker; + + assert(size); + + if (ppv == NULL) { + error_setg(errp, "vmstate: get_maybeptr must be called with ppv != NULL"); + return false; + } + + /* + * We start from a clean array, all elements must be NULL, unless + * something we haven't prepared for has changed in vmstate_save_state_v(). + * Let's check for this just in case. + */ + if (*(void **)ppv != NULL) { + error_setg(errp, "vmstate: get_maybeptr must be called with *ppv == NULL"); + return false; + } + + marker = qemu_get_byte(f); + assert(marker == VMS_NULLPTR_MARKER || marker == VMS_NOTNULLPTR_MARKER); + + if (marker == VMS_NOTNULLPTR_MARKER) { + void *pv; + + /* allocate memory for structure */ + pv = g_malloc0(size); + + ok = vmstate_load_field(f, pv, size, real_field, errp); + if (!ok) { + g_free(pv); + return false; + } + + *(void **)ppv = pv; + } + + return true; +} + +static bool save_maybeptr(QEMUFile *f, void *ppv, size_t unused_size, + const VMStateField *field, JSONWriter *vmdesc, + Error **errp) +{ + const VMStateField *real_field = field->real_field; + /* size of structure pointed to by elements of array */ + size_t size = real_field->start; + void *pv; + + assert(size); + + /* + * (ppv) is an address of an i-th element of a dynamic array. + * + * (ppv) can not be NULL unless we have some regression/bug in + * vmstate_save_state_v(), because it is result of pointer arithemic like: + * first_elem + size * i. + */ + if (ppv == NULL) { + error_setg(errp, "vmstate: put_maybeptr must be called with ppv != NULL"); + return false; + } + + /* get a pointer to a structure */ + pv = *(void **)ppv; + + if (pv == NULL) { + /* write a mark telling that there was a NULL pointer */ + qemu_put_byte(f, VMS_NULLPTR_MARKER); + return true; + } + + /* if pv is not NULL, write a marker and save field using vmstate_save_field() */ + qemu_put_byte(f, VMS_NOTNULLPTR_MARKER); + + return vmstate_save_field(f, pv, size, real_field, vmdesc, errp); +} + +const VMStateInfo vmstate_info_maybeptr = { + .name = "maybeptr", + .load = load_maybeptr, + .save = save_maybeptr, +}; + /* 64 bit unsigned int. See that the received value is the same than the one in the field */ diff --git a/migration/vmstate.c b/migration/vmstate.c index 616eb310e61..29e63751105 100644 --- a/migration/vmstate.c +++ b/migration/vmstate.c @@ -74,10 +74,15 @@ vmsd_create_fake_nullptr_field(const VMStateField *field) /* Do not need "field_exists" check as it always exists (which is null) */ fake->field_exists = NULL; - /* See vmstate_info_nullptr - use 1 byte to represent nullptr */ - fake->size = 1; - fake->info = &vmstate_info_nullptr; - fake->flags = VMS_SINGLE; + if (!(field->flags & VMS_ARRAY_OF_POINTER_ALLOW_NULL)) { + /* See vmstate_info_nullptr - use 1 byte to represent nullptr */ + fake->size = 1; + fake->info = &vmstate_info_nullptr; + fake->flags = VMS_SINGLE; + } else { + fake->real_field = field; + fake->info = &vmstate_info_maybeptr; + } /* All the rest fields shouldn't matter.. */ @@ -258,13 +263,28 @@ bool vmstate_load_vmsd(QEMUFile *f, const VMStateDescription *vmsd, for (i = 0; i < n_elems; i++) { bool ok; void *curr_elem = first_elem + size * i; + bool need_fake_field = false; const VMStateField *inner_field; if (field->flags & VMS_ARRAY_OF_POINTER) { - curr_elem = *(void **)curr_elem; + if (!(field->flags & VMS_ARRAY_OF_POINTER_ALLOW_NULL)) { + assert(curr_elem); + curr_elem = *(void **)curr_elem; + need_fake_field = !curr_elem; + } else { + /* + * We expect array of pointers to be initialized. + * We don't want to overwrite curr_elem with it's + * dereferenced value, because we may need to + * allocate memory (depending on what is in the migration + * stream) and write to it later. + */ + assert(!*(void **)curr_elem); + need_fake_field = true; + } } - if (!curr_elem && size) { + if (need_fake_field && size) { /* * If null pointer found (which should only happen in * an array of pointers), use null placeholder and do @@ -272,6 +292,7 @@ bool vmstate_load_vmsd(QEMUFile *f, const VMStateDescription *vmsd, */ inner_field = vmsd_create_fake_nullptr_field(field); } else { + assert(curr_elem || !size); inner_field = field; } @@ -546,25 +567,38 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VMStateDescription *vmsd, for (i = 0; i < n_elems; i++) { void *curr_elem = first_elem + size * i; + bool need_fake_field = false; const VMStateField *inner_field; bool is_null; int max_elems = n_elems - i; old_offset = qemu_file_transferred(f); if (field->flags & VMS_ARRAY_OF_POINTER) { - assert(curr_elem); - curr_elem = *(void **)curr_elem; + if (!(field->flags & VMS_ARRAY_OF_POINTER_ALLOW_NULL)) { + assert(curr_elem); + curr_elem = *(void **)curr_elem; + need_fake_field = !curr_elem; + } else { + /* + * We always need a fake field to properly handle + * VMS_ARRAY_OF_POINTER_ALLOW_NULL case, because + * even if pointer is not NULL, we still want to + * write a marker in the migration stream. + */ + need_fake_field = true; + } } - if (!curr_elem && size) { + if (need_fake_field && size) { /* * If null pointer found (which should only happen in * an array of pointers), use null placeholder and do * not follow. */ inner_field = vmsd_create_fake_nullptr_field(field); - is_null = true; + is_null = !curr_elem; } else { + assert(curr_elem || !size); inner_field = field; is_null = false; } -- 2.47.3