On 5/20/20 12:01 AM, Laszlo Ersek wrote:
> On 05/19/20 20:20, Philippe Mathieu-Daudé wrote:
>> The FW_CFG_DATA_GENERATOR allow any object to product
>
> (1) I suggest:
>
> s/allow/allows/
> s/product/produce/
>
>> blob of data consumable by the fw_cfg device.
>>
>> Signed-off-by: Philippe Mathieu-Daudé <phi...@redhat.com>
>> ---
>> include/hw/nvram/fw_cfg.h | 49 +++++++++++++++++++++++++++++++++++++++
>> hw/nvram/fw_cfg.c | 30 ++++++++++++++++++++++++
>> 2 files changed, 79 insertions(+)
>>
>> diff --git a/include/hw/nvram/fw_cfg.h b/include/hw/nvram/fw_cfg.h
>> index 25d9307018..74b4790fae 100644
>> --- a/include/hw/nvram/fw_cfg.h
>> +++ b/include/hw/nvram/fw_cfg.h
>> @@ -9,11 +9,40 @@
>> #define TYPE_FW_CFG "fw_cfg"
>> #define TYPE_FW_CFG_IO "fw_cfg_io"
>> #define TYPE_FW_CFG_MEM "fw_cfg_mem"
>> +#define TYPE_FW_CFG_DATA_GENERATOR_INTERFACE "fw_cfg-data-generator"
>>
>> #define FW_CFG(obj) OBJECT_CHECK(FWCfgState, (obj), TYPE_FW_CFG)
>> #define FW_CFG_IO(obj) OBJECT_CHECK(FWCfgIoState, (obj), TYPE_FW_CFG_IO)
>> #define FW_CFG_MEM(obj) OBJECT_CHECK(FWCfgMemState, (obj), TYPE_FW_CFG_MEM)
>>
>> +#define FW_CFG_DATA_GENERATOR_CLASS(class) \
>> + OBJECT_CLASS_CHECK(FWCfgDataGeneratorClass, (class), \
>> + TYPE_FW_CFG_DATA_GENERATOR_INTERFACE)
>> +#define FW_CFG_DATA_GENERATOR_GET_CLASS(obj) \
>> + OBJECT_GET_CLASS(FWCfgDataGeneratorClass, (obj), \
>> + TYPE_FW_CFG_DATA_GENERATOR_INTERFACE)
>> +
>> +typedef struct FWCfgDataGeneratorClass {
>> + /*< private >*/
>> + InterfaceClass parent_class;
>> + /*< public >*/
>> +
>> + /**
>> + * get_data:
>> + * @obj: the object implementing this interface
>> + *
>> + * Returns: pointer to start of the generated item data
>> + */
>> + const void *(*get_data)(Object *obj);
>
> I'm not familiar with QOM, so please excuse any dumb questions.
>
> "const" suggests the blob returned remains owned by "obj";
Yes, it is owned by the generator object.
fw_cfg_add_from_generator() does a memdup().
> that answers
> the question whether the caller should attempt to free the blob. (The
> answer is "no".)
>
> (2) However, will this perhaps expose other functions, currently taking
> non-const-qualified pointers, to which we'd like to pass the blob
> returned by the above member function?
>
> Because, then we'd have to cast away "const",
It is illegal to cast away "const". This is why I choose to use it here,
if the consumer want to modify it, it is forced to make its own copy.
> and I find that much
> uglier than removing the "const" from *here*, and adding a more verbose
> comment as replacement.
>
> Yes, this is clearly speculation -- IOW just a question. If all the
> functions we're going to pass the return value to are fine with
> pointer-to-const, then this interface should be OK.
The only user so far uses memdup().
>
> (Obviously when I say "cast away const", I think of functions that do
> not actually modify the object pointed-to by the non-const-qualified
> pointer.)
>
>> + /**
>> + * get_length:
>> + * @obj: the object implementing this interface
>> + *
>> + * Returns: the size of the generated item data in bytes
>> + */
>> + size_t (*get_length)(Object *obj);
>> +} FWCfgDataGeneratorClass;
>> +
>> typedef struct fw_cfg_file FWCfgFile;
>>
>> #define FW_CFG_ORDER_OVERRIDE_VGA 70
>> @@ -263,6 +292,26 @@ void fw_cfg_add_file_callback(FWCfgState *s, const char
>> *filename,
>> void *fw_cfg_modify_file(FWCfgState *s, const char *filename, void *data,
>> size_t len);
>>
>> +/**
>> + * fw_cfg_add_from_generator:
>> + * @s: fw_cfg device being modified
>> + * @filename: name of new fw_cfg file item
>> + * @generator_id: name of object implementing FW_CFG_DATA_GENERATOR
>> interface
>> + * @errp: pointer to a NULL initialized error object
>> + *
>> + * Add a new NAMED fw_cfg item with the content generated from the
>> + * @generator_id object. The data referenced by the starting pointer is
>> copied
>
> (3) s/referenced by the starting pointer/generated by the @generator_id
> object/
>
>> + * into the data structure of the fw_cfg device.
>> + * The next available (unused) selector key starting at FW_CFG_FILE_FIRST
>> + * will be used; also, a new entry will be added to the file directory
>> + * structure residing at key value FW_CFG_FILE_DIR, containing the item
>> name,
>> + * data size, and assigned selector key value.
>> + *
>> + * Returns: the size of the generated item data on success, -1 otherwise.
>
> (4) I don't like ssize_t for a return value like this.
>
> First, get_length() returns size_t, which may not be representable in an
> ssize_t.
>
> (Actually, it's worse than that; POSIX says, "the type ssize_t shall be
> capable of storing values at least in the range [-1, {SSIZE_MAX}]" --
> and if I run "getconf SSIZE_MAX", I get 32767. Indeed, _POSIX_SSIZE_MAX,
> which is the minimum for any implementation's SSIZE_MAX, is 32767.)
>
> Second, is a zero-sized blob useful in fw_cfg (from a generator)?
Not for now. We can add it later anyway.
>
> If it is not useful, then this function should return size_t, and use
> retval=0 for signaling an error.
OK.
>
> If a zero-sized blob is useful, then the function should return a bool
> (in addition to producing "errp"), and output the blob size as a
> separate parameter.
>
>> + */
>> +ssize_t fw_cfg_add_from_generator(FWCfgState *s, const char *filename,
>> + const char *generator_id, Error **errp);
>> +
>> FWCfgState *fw_cfg_init_io_dma(uint32_t iobase, uint32_t dma_iobase,
>> AddressSpace *dma_as);
>> FWCfgState *fw_cfg_init_io(uint32_t iobase);
>> diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
>> index 8dd50c2c72..e18cb074df 100644
>> --- a/hw/nvram/fw_cfg.c
>> +++ b/hw/nvram/fw_cfg.c
>> @@ -1032,6 +1032,30 @@ void *fw_cfg_modify_file(FWCfgState *s, const char
>> *filename,
>> return NULL;
>> }
>>
>> +ssize_t fw_cfg_add_from_generator(FWCfgState *s, const char *filename,
>> + const char *generator_id, Error **errp)
>> +{
>> + FWCfgDataGeneratorClass *k;
>> + Object *o;
>
> (5) Not sure about QEMU coding standards, but the above single-char
> variable names (especially "o") terrify me. Please use "klass" and "obj".
>
> Do ignore my request if these variable names are just fine in QEMU.
I don't want to terrify you :P
>
>> + size_t sz;
>> +
>> + o = object_resolve_path_component(object_get_objects_root(),
>> generator_id);
>> + if (!o) {
>> + error_setg(errp, "Cannot find object ID %s", generator_id);
>> + return -1;
>> + }
>> + if (!object_dynamic_cast(o, TYPE_FW_CFG_DATA_GENERATOR_INTERFACE)) {
>> + error_setg(errp, "Object '%s' is not a fw_cfg-data-generator
>> subclass",
>> + generator_id);
>
> (6) We should probably not open code
> TYPE_FW_CFG_DATA_GENERATOR_INTERFACE as "fw_cfg-data-generator" even in
> the error message.
>
> (7) If this branch is taken, would that arguably merit an assertion
> failure? I mean, can the dynamic cast fail without QEMU having a related
> bug somewhere? (Maybe this is going to be answered in the rest of the
> series.) Because I see those OBJECT_CHECK macros near the top of
> "fw_cfg.h", and those boil down to object_dynamic_cast_assert().
>
>> + return -1;
>> + }
>> + k = FW_CFG_DATA_GENERATOR_GET_CLASS(o);
>> + sz = k->get_length(o);
>> + fw_cfg_add_file(s, filename, g_memdup(k->get_data(o), sz), sz);
>
> (g_memdup() takes a "guint" for "byte_size". Whether that matches
> "size_t" is anyone's guess. I guess it can't be helped.)
Similarly it returns a gpointer...
>
>> +
>> + return sz;
>
> Right, this is the size_t --> ssize_t conversion that makes me
> uncomfortable.
>
> I'm OK if you ignore all of my comments, these are simply the thoughts
> that crossed my mind.
Thanks for them!
Regards,
Phil.
>
> Thanks
> Laszlo
>
>> +}
>> +
>> static void fw_cfg_machine_reset(void *opaque)
>> {
>> MachineClass *mc = MACHINE_GET_CLASS(qdev_get_machine());
>> @@ -1333,12 +1357,18 @@ static const TypeInfo fw_cfg_mem_info = {
>> .class_init = fw_cfg_mem_class_init,
>> };
>>
>> +static const TypeInfo fw_cfg_data_generator_interface_info = {
>> + .name = TYPE_FW_CFG_DATA_GENERATOR_INTERFACE,
>> + .parent = TYPE_INTERFACE,
>> + .class_size = sizeof(FWCfgDataGeneratorClass),
>> +};
>>
>> static void fw_cfg_register_types(void)
>> {
>> type_register_static(&fw_cfg_info);
>> type_register_static(&fw_cfg_io_info);
>> type_register_static(&fw_cfg_mem_info);
>> + type_register_static(&fw_cfg_data_generator_interface_info);
>> }
>>
>> type_init(fw_cfg_register_types)
>>
>
