From e86c004fbda963191298905d7e02f8efdb0d05cc Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Wed, 1 Apr 2026 16:28:40 -0400 Subject: [PATCH] vmstate: Allow vmstate_info_nullptr to emit non-NULL markers 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 Reviewed-by: Juraj Marcin Link: https://lore.kernel.org/qemu-devel/20260401202844.673494-8-peterx@redhat.com Signed-off-by: Fabiano Rosas --- 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; -/** 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 b274204e66..b333aa1744 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); @@ -71,12 +71,12 @@ vmsd_create_fake_nullptr_field(const VMStateField *field) fake->name = field->name; fake->version_id = field->version_id; - /* 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 = NULL; - /* See vmstate_info_nullptr - use 1 byte to represent nullptr */ + /* See vmstate_info_ptr_marker - use 1 byte to represent ptr status */ 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; } @@ -583,26 +583,27 @@ 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; const VMStateField *inner_field; - bool is_null; /* maximum number of elements to compress in the JSON blob */ int max_elems = vmsd_can_compress(field) ? (n_elems - i) : 1; + bool use_marker_field, is_null; if (field->flags & VMS_ARRAY_OF_POINTER) { assert(curr_elem); curr_elem = *(void **)curr_elem; } - if (!curr_elem && size) { + is_null = !curr_elem && size; + use_marker_field = 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 = vmsd_create_fake_nullptr_field(field); - is_null = true; + inner_field = vmsd_create_ptr_marker_field(field); } else { inner_field = field; - is_null = false; } /* @@ -638,7 +639,7 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VMStateDescription *vmsd, i, max_elems, errp); /* 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); } 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 @@ class VMSDFieldIntLE(VMSDFieldInt): super(VMSDFieldIntLE, self).__init__(desc, file) self.dtype = '