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Tue, 19 May 2020 22:01:06 +0000 (UTC) Subject: Re: [PATCH v6 1/5] hw/nvram/fw_cfg: Add the FW_CFG_DATA_GENERATOR interface To: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , qemu-devel@nongnu.org References: <20200519182024.14638-1-philmd@redhat.com> <20200519182024.14638-2-philmd@redhat.com> From: Laszlo Ersek Message-ID: <845b9e8e-0925-da57-a484-3a96d554432d@redhat.com> Date: Wed, 20 May 2020 00:01:06 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20200519182024.14638-2-philmd@redhat.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=205.139.110.120; envelope-from=lersek@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/18 23:56:10 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Paolo Bonzini , "=?UTF-8?Q?Daniel_P._Berrang=c3=a9?=" , Eduardo Habkost , Gerd Hoffmann Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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 > --- > 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"; 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", 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. (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)? If it is not useful, then this function should return size_t, and use retval=0 for signaling an error. 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. > + 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.) > + > + 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 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) >