Em Sun, 3 Sep 2017 22:05:23 +0200 Honza Petrouš <jpetrous@xxxxxxxxx> escreveu: > > There is still a gap at the CA API, as there are three ioctls that are used > > only by a few drivers and whose structs are not properly documented: > > CA_GET_MSG, CA_SEND_MSG and CA_SET_DESCR. > > > > The first two ones seem to be related to a way that a few drivers > > provide to send/receive messages. > > I never seen usage of such R/W ioctls, all drivers I have access to > are using read()/write() variant of communication. Yeah, the normal usage is to use R/W syscalls. > BTW, I just remembered dvblast app, part of videolan.org: > > http://www.videolan.org/projects/dvblast.html > > which is using CA_GET_MSG/CA_SEND_MSG: > > https://code.videolan.org/videolan/dvblast/blob/master/en50221.c >From the ca_msg struct: /* a message to/from a CI-CAM */ struct ca_msg { unsigned int index; unsigned int type; unsigned int length; unsigned char msg[256]; }; It only uses length and msg fields. Describing those seem quite obvious. However, what "index" and "type" means? Within the Kernel, only two drivers implement it: $ git grep -l ca_msg drivers/ drivers/media/firewire/firedtv-ci.c drivers/media/pci/bt8xx/dst_ca.c At the dst_ca driver, checking for those fields don't give any useful result: $ grep index drivers/media/pci/bt8xx/dst_ca.c (nothing) $ grep type drivers/media/pci/bt8xx/dst_ca.c // Copy application_type, application_manufacturer and manufacturer_code p_ca_caps->slot_type = 1; p_ca_caps->descr_type = 1; p_ca_slot_info->type = CA_CI; p_ca_slot_info->type = CA_CI; (btw, using "1" for slot_type and descr_type there seems a very bad thing) The code at ca_get_message(), handle_dst_tag(), ca_set_pmt(), etc also doesn't seem to be using neither one of those fields. The same happens at firedtv-ci: it also doesn't seem to be using none of those fields. It should be noticed that, the dst_ca seems to allow more than one descrambler: p_ca_caps->descr_num = slot_cap[7]; Yet, the index is not used. So, it doesn't seem to be related to the descrambler index (or there's an implementation bug there - and at dvblast - as none uses it). What *I* suspect is that this were meant to be used for either CA index/type or DESCR index/type, but, when this got implemented, people discovered that this would be useless and never actually used those fields. Yet, I may be completely wrong and those were added to mean something else. If so, then we could just change the struct to: struct ca_msg { unsigned int reserved[2]; unsigned int length; unsigned char msg[256]; }; And document just length and msg. Thanks, Mauro -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
