* Introduction * OpenWrt heavily uses blob-s and blobmsg-s implemented in libubox. They are used in ubus and when parsing JSON-s.
Short summary for two formats by Jo: [14:51] <jow> I think a blobmsg is a structure nested into a blob [14:52] <jow> a blob is id_len (8 bits type (aka ID), 24 bits length) + data payload [14:53] <jow> a blobmsg follows the id_len and consists of a name_len (16bit) and a variable length name string [14:53] <jow> any payload data then follows the variable length name (32bit aligned) [14:54] <jow> I think the extra set of blobmsg_*() apis is needed to handle the blob attributes while somehow transparently dealing with the name TLV squeezed in front [14:55] <jow> due to that, there's different notions of "payload" [14:55] <jow> a blob payload is simply the data after the id_len member (pointing to the start of the blobmsg hdr) [14:56] <jow> a blobmsg payload is the actual payload after the id_len member, the namelen member and the variable length name * Problem * Some/many developers are confused regarding what do they deal with (blob vs. blobmsg). There is single struct blob_attr that gets passed around but it isn't clear if it contains blob or blobmsg. Depending on blob vs. blobmsg type a correct set of API functions should be used. E.g. 1. blob_len() vs. blobmsg_data_len() 2. blob_for_each_attr() vs. blobmsg_for_each_attr() There are many cases where blobmsg_data() is used for blob format. It works thanks to some extra check in the blobmsg_data(). Naming is confusing too: 1. "blobmsg" could be "namedblob" or "blob_named" or "blob_with_name" 2. blobmsg_parse() requires passing *blob* data not blobmsg data * Cleaning API usage * One idea for cleaning up blob(msg) dependant code was to make it always call right functions (blob_* for blob and blobmsg_* for blobmsg). I started looking at this but it's not that obvious. I realized that ubus method handlers always receive struct blob_attr that is *blob*. Some projects call blobmsg_data() and blobmsg_len() on it that isn't 100% clean solution. Of course having blobmsg_parse() name doesn't help. I planned to replace all such blobmsg_data() calls with blob_data() but then I realized that *nested* tables will actually need blobmsg_data(). Parsing fails if blobmsg data gets passed. * Looking for ideas * I'm looking for ideas how to simplify and clean blob(msg) API. The only idea I have is merging blob & blogmsg APIs so all functions get aware of both types. I suggested that but Felix pointed out it's not a good idea: [17:12] <nbd> not sure if that makes sense, they're used differently [17:12] <nbd> blob is indexed by id [17:12] <nbd> in blobmsg, the id specifies the type and fields are indexed by name (...) [17:39] <nbd> well, blobmsg is a layer around blob [17:39] <nbd> so i don't think the blob api should deal with blobmsg specifics directly Any suggestions? _______________________________________________ openwrt-devel mailing list openwrt-devel@lists.openwrt.org https://lists.openwrt.org/mailman/listinfo/openwrt-devel
