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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-vse= mentsov@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 =3D 0x8000, =20 /* Marker for end of list */ - VMS_END =3D 0x10000 + VMS_END =3D 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 expli= citly. */ + VMS_ARRAY_OF_POINTER_ALLOW_NULL =3D 0x20000, }; =20 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; }; =20 struct VMStateDescription { @@ -268,8 +281,10 @@ extern const VMStateInfo vmstate_info_uint64; extern const VMStateInfo vmstate_info_fd; =20 /** 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; =20 extern const VMStateInfo vmstate_info_cpudouble; =20 @@ -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; =20 #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 =3D vmstate_offset_array(_s, _f, _type*, _n), \ } =20 +/* + * For migrating a dynamically allocated uint{8,32}-indexed array + * of pointers to structures (with NULL entries and with auto memory alloc= ation). + * + * _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, _f= ield_num, _version, _vmsd, _type) { \ + .name =3D (stringify(_field)), \ + .version_id =3D (_version), \ + .num_offset =3D vmstate_offset_value(_state, _field_num, uint8_t), \ + .vmsd =3D &(_vmsd), \ + .start =3D sizeof(_type), \ + .size =3D sizeof(_type *), \ + .flags =3D VMS_POINTER|VMS_VARRAY_UINT8|VMS_ARRAY_OF_POINTER| \ + VMS_ARRAY_OF_POINTER_ALLOW_NULL|VMS_STRUCT, \ + .offset =3D vmstate_offset_pointer(_state, _field, _type *), \ +} + +#define VMSTATE_VARRAY_OF_POINTER_UINT8_ALLOC(_field, _state, _field_num, = _version, _info, _type) { \ + .name =3D (stringify(_field)), \ + .version_id =3D (_version), \ + .num_offset =3D vmstate_offset_value(_state, _field_num, uint8_t), \ + .info =3D &(_info), \ + .start =3D sizeof(_type), \ + .size =3D sizeof(_type *), \ + .flags =3D VMS_POINTER|VMS_VARRAY_UINT8|VMS_ARRAY_OF_POINTER| \ + VMS_ARRAY_OF_POINTER_ALLOW_NULL, \ + .offset =3D vmstate_offset_pointer(_state, _field, _type *), \ +} + +#define VMSTATE_VARRAY_OF_POINTER_TO_STRUCT_UINT32_ALLOC(_field, _state, _= field_num, _version, _vmsd, _type) { \ + .name =3D (stringify(_field)), \ + .version_id =3D (_version), \ + .num_offset =3D vmstate_offset_value(_state, _field_num, uint32_t), \ + .vmsd =3D &(_vmsd), \ + .start =3D sizeof(_type), \ + .size =3D sizeof(_type *), \ + .flags =3D VMS_POINTER|VMS_VARRAY_UINT32|VMS_ARRAY_OF_POINTER| \ + VMS_ARRAY_OF_POINTER_ALLOW_NULL|VMS_STRUCT, \ + .offset =3D vmstate_offset_pointer(_state, _field, _type *), \ +} + +#define VMSTATE_VARRAY_OF_POINTER_UINT32_ALLOC(_field, _state, _field_num,= _version, _info, _type) { \ + .name =3D (stringify(_field)), \ + .version_id =3D (_version), \ + .num_offset =3D vmstate_offset_value(_state, _field_num, uint32_t), \ + .info =3D &(_info), \ + .start =3D sizeof(_type), \ + .size =3D sizeof(_type *), \ + .flags =3D VMS_POINTER|VMS_VARRAY_UINT32|VMS_ARRAY_OF_POINTER| \ + VMS_ARRAY_OF_POINTER_ALLOW_NULL, \ + .offset =3D vmstate_offset_pointer(_state, _field, _type *), \ +} + #define VMSTATE_VARRAY_OF_POINTER_UINT32(_field, _state, _field_num, _vers= ion, _info, _type) { \ .name =3D (stringify(_field)), = \ .version_id =3D (_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 *vm= sd) =20 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_UIN= T32)))); + + /* + * 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 membe= r. + */ + 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_fiel= d(). + */ + 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 =3D { .save =3D save_nullptr, }; =20 +static bool load_maybeptr(QEMUFile *f, void *ppv, size_t unused_size, + const VMStateField *field, Error **errp) +{ + bool ok =3D false; + const VMStateField *real_field =3D field->real_field; + /* size of structure pointed to by elements of array */ + size_t size =3D real_field->start; + int marker; + + assert(size); + + if (ppv =3D=3D NULL) { + error_setg(errp, "vmstate: get_maybeptr must be called with ppv != =3D 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 !=3D NULL) { + error_setg(errp, "vmstate: get_maybeptr must be called with *ppv = =3D=3D NULL"); + return false; + } + + marker =3D qemu_get_byte(f); + assert(marker =3D=3D VMS_NULLPTR_MARKER || marker =3D=3D VMS_NOTNULLPT= R_MARKER); + + if (marker =3D=3D VMS_NOTNULLPTR_MARKER) { + void *pv; + + /* allocate memory for structure */ + pv =3D g_malloc0(size); + + ok =3D vmstate_load_field(f, pv, size, real_field, errp); + if (!ok) { + g_free(pv); + return false; + } + + *(void **)ppv =3D 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 =3D field->real_field; + /* size of structure pointed to by elements of array */ + size_t size =3D 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 l= ike: + * first_elem + size * i. + */ + if (ppv =3D=3D NULL) { + error_setg(errp, "vmstate: put_maybeptr must be called with ppv != =3D NULL"); + return false; + } + + /* get a pointer to a structure */ + pv =3D *(void **)ppv; + + if (pv =3D=3D 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 =3D { + .name =3D "maybeptr", + .load =3D load_maybeptr, + .save =3D save_maybeptr, +}; + /* 64 bit unsigned int. See that the received value is the same than the o= ne in the field */ =20 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 *fiel= d) /* Do not need "field_exists" check as it always exists (which is null= ) */ fake->field_exists =3D NULL; =20 - /* See vmstate_info_nullptr - use 1 byte to represent nullptr */ - fake->size =3D 1; - fake->info =3D &vmstate_info_nullptr; - fake->flags =3D VMS_SINGLE; + if (!(field->flags & VMS_ARRAY_OF_POINTER_ALLOW_NULL)) { + /* See vmstate_info_nullptr - use 1 byte to represent nullptr */ + fake->size =3D 1; + fake->info =3D &vmstate_info_nullptr; + fake->flags =3D VMS_SINGLE; + } else { + fake->real_field =3D field; + fake->info =3D &vmstate_info_maybeptr; + } =20 /* All the rest fields shouldn't matter.. */ =20 @@ -258,13 +263,28 @@ bool vmstate_load_vmsd(QEMUFile *f, const VMStateDesc= ription *vmsd, for (i =3D 0; i < n_elems; i++) { bool ok; void *curr_elem =3D first_elem + size * i; + bool need_fake_field =3D false; const VMStateField *inner_field; =20 if (field->flags & VMS_ARRAY_OF_POINTER) { - curr_elem =3D *(void **)curr_elem; + if (!(field->flags & VMS_ARRAY_OF_POINTER_ALLOW_NULL))= { + assert(curr_elem); + curr_elem =3D *(void **)curr_elem; + need_fake_field =3D !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 mi= gration + * stream) and write to it later. + */ + assert(!*(void **)curr_elem); + need_fake_field =3D true; + } } =20 - 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 VMStateDescri= ption *vmsd, */ inner_field =3D vmsd_create_fake_nullptr_field(field); } else { + assert(curr_elem || !size); inner_field =3D field; } =20 @@ -546,25 +567,38 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VM= StateDescription *vmsd, =20 for (i =3D 0; i < n_elems; i++) { void *curr_elem =3D first_elem + size * i; + bool need_fake_field =3D false; const VMStateField *inner_field; bool is_null; int max_elems =3D n_elems - i; =20 old_offset =3D qemu_file_transferred(f); if (field->flags & VMS_ARRAY_OF_POINTER) { - assert(curr_elem); - curr_elem =3D *(void **)curr_elem; + if (!(field->flags & VMS_ARRAY_OF_POINTER_ALLOW_NULL))= { + assert(curr_elem); + curr_elem =3D *(void **)curr_elem; + need_fake_field =3D !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 =3D true; + } } =20 - 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 =3D vmsd_create_fake_nullptr_field(field); - is_null =3D true; + is_null =3D !curr_elem; } else { + assert(curr_elem || !size); inner_field =3D field; is_null =3D false; } --=20 2.47.3