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Tue, 16 Jun 2020 15:31:26 +0000 (UTC) Date: Tue, 16 Jun 2020 16:31:22 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Subject: Re: [PATCH v9 1/5] hw/nvram/fw_cfg: Add the FW_CFG_DATA_GENERATOR interface Message-ID: <20200616153122.GN550360@redhat.com> References: <20200615103457.25282-1-philmd@redhat.com> <20200615103457.25282-2-philmd@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200615103457.25282-2-philmd@redhat.com> User-Agent: Mutt/1.14.0 (2020-05-02) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Received-SPF: pass client-ip=205.139.110.61; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/16 02:01:17 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Paolo Bonzini , Laszlo Ersek , qemu-devel@nongnu.org, Gerd Hoffmann Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Jun 15, 2020 at 12:34:53PM +0200, Philippe Mathieu-Daudé wrote: > The FW_CFG_DATA_GENERATOR allows any object to produce > blob of data consumable by the fw_cfg device. > > Reviewed-by: Laszlo Ersek > Signed-off-by: Philippe Mathieu-Daudé > --- > docs/specs/fw_cfg.txt | 9 ++++++- > include/hw/nvram/fw_cfg.h | 52 +++++++++++++++++++++++++++++++++++++++ > hw/nvram/fw_cfg.c | 36 +++++++++++++++++++++++++++ > 3 files changed, 96 insertions(+), 1 deletion(-) > > diff --git a/docs/specs/fw_cfg.txt b/docs/specs/fw_cfg.txt > index 8f1ebc66fa..bc16daa38a 100644 > --- a/docs/specs/fw_cfg.txt > +++ b/docs/specs/fw_cfg.txt > @@ -219,7 +219,7 @@ To check the result, read the "control" field: > > = Externally Provided Items = > > -As of v2.4, "file" fw_cfg items (i.e., items with selector keys above > +Since v2.4, "file" fw_cfg items (i.e., items with selector keys above > FW_CFG_FILE_FIRST, and with a corresponding entry in the fw_cfg file > directory structure) may be inserted via the QEMU command line, using > the following syntax: > @@ -230,6 +230,13 @@ Or > > -fw_cfg [name=],string= > > +Since v5.1, QEMU allows some objects to generate fw_cfg-specific content, > +the content is then associated with a "file" item using the 'gen_id' option > +in the command line, using the following syntax: > + > + -object ,id=,[generator-specific-options] \ > + -fw_cfg [name=],gen_id= > + > See QEMU man page for more documentation. > > Using item_name with plain ASCII characters only is recommended. > diff --git a/include/hw/nvram/fw_cfg.h b/include/hw/nvram/fw_cfg.h > index 25d9307018..ca69666847 100644 > --- a/include/hw/nvram/fw_cfg.h > +++ b/include/hw/nvram/fw_cfg.h > @@ -9,11 +9,43 @@ > #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 > + * > + * The returned pointer is a QObject weak reference, @obj owns > + * the reference and may free it at any time in the future. This description is a bit odd. We're just returning a plain byte array pointer, not a QObject, nor a reference, not will it be free'd at any time. > + */ > + const void *(*get_data)(Object *obj); > + /** > + * get_length: > + * @obj: the object implementing this interface > + * > + * Returns: the size of the generated item data in bytes > + */ > + size_t (*get_length)(Object *obj); I'd be inclined to have a single method that returns a GByteArray, instead of separate methods for data & length. That gives you a sized byte array, with a well define lifetime, which is what the caller really wants here. ie /** * get_data: * @obj: the object implementing this interface * * Returns: reference to a byte array containing the data. * The caller should release the reference when no longer * required. */ GByteArray *(*get_data)(Object *obj); > +} FWCfgDataGeneratorClass; > + .... > +size_t fw_cfg_add_from_generator(FWCfgState *s, const char *filename, > + const char *gen_id, Error **errp) > +{ > + FWCfgDataGeneratorClass *klass; > + Object *obj; > + size_t size; > + > + obj = object_resolve_path_component(object_get_objects_root(), gen_id); > + if (!obj) { > + error_setg(errp, "Cannot find object ID '%s'", gen_id); > + return 0; > + } > + if (!object_dynamic_cast(obj, TYPE_FW_CFG_DATA_GENERATOR_INTERFACE)) { > + error_setg(errp, "Object ID '%s' is not a '%s' subclass", > + gen_id, TYPE_FW_CFG_DATA_GENERATOR_INTERFACE); > + return 0; > + } > + klass = FW_CFG_DATA_GENERATOR_GET_CLASS(obj); ...then the following: > + size = klass->get_length(obj); > + if (size == 0) { > + error_setg(errp, "Object ID '%s' failed to generate fw_cfg data", > + gen_id); > + return 0; > + } > + fw_cfg_add_file(s, filename, g_memdup(klass->get_data(obj), (guint)size), > + size); Can be replaced with: g_autoptr(GByteArray) data = klass->get_data(obj); fw_cfg_add_file(s, filename, g_byte_array_steal(data, NULL), (guint)g_byte_array_get_size(data)); If there's a real possibility of failure, then an 'Error **errp' should be added to the 'get_data' method, so this code doesn't have to invent a error message with no useful info on the real failure. > + > + return size; > +} > + Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|