Expose additional socket constants for CAN_BCM flags

[karlding]

BPO	37085
Nosy	@taleinat, @ambv, @miss-islington, @karlding
PRs	bpo-37085: Expose SocketCAN bcm_msg_head flags #13646 [3.8] bpo-37085: Expose SocketCAN bcm_msg_head flags (GH-13646) #15049

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2019-07-31.12:04:47.124>
created_at = <Date 2019-05-29.06:53:00.895>
labels = ['3.8', 'type-feature', 'library', '3.9']
title = 'Expose additional socket constants for CAN_BCM flags'
updated_at = <Date 2019-07-31.12:04:47.003>
user = 'https://github.com/karlding'

bugs.python.org fields:

activity = <Date 2019-07-31.12:04:47.003>
actor = 'taleinat'
assignee = 'none'
closed = True
closed_date = <Date 2019-07-31.12:04:47.124>
closer = 'taleinat'
components = ['Library (Lib)']
creation = <Date 2019-05-29.06:53:00.895>
creator = 'karlding'
dependencies = []
files = []
hgrepos = []
issue_num = 37085
keywords = ['patch']
message_count = 4.0
messages = ['343865', '348792', '348793', '348799']
nosy_count = 4.0
nosy_names = ['taleinat', 'lukasz.langa', 'miss-islington', 'karlding']
pr_nums = ['13646', '15049']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue37085'
versions = ['Python 3.8', 'Python 3.9']

[karlding]

When reading through the values exposed via the socket library, I noticed that currently, only the SocketCAN BCM opcode enums are exposed via the socket constants. These correspond to the following from the Linux headers:

    enum {
    	TX_SETUP = 1,	/* create (cyclic) transmission task */
    	TX_DELETE,	/* remove (cyclic) transmission task */
    	TX_READ,	/* read properties of (cyclic) transmission task */
    	TX_SEND,	/* send one CAN frame */
    	RX_SETUP,	/* create RX content filter subscription */
    	RX_DELETE,	/* remove RX content filter subscription */
    	RX_READ,	/* read properties of RX content filter subscription */
    	TX_STATUS,	/* reply to TX_READ request */
    	TX_EXPIRED,	/* notification on performed transmissions (count=0) */
    	RX_STATUS,	/* reply to RX_READ request */
    	RX_TIMEOUT,	/* cyclic message is absent */
    	RX_CHANGED	/* updated CAN frame (detected content change) */
    };

It would be nice to expose the BCM flags #defines as well.

        #define SETTIMER            0x0001
        #define STARTTIMER          0x0002
        #define TX_COUNTEVT         0x0004
        #define TX_ANNOUNCE         0x0008
        #define TX_CP_CAN_ID        0x0010
        #define RX_FILTER_ID        0x0020
        #define RX_CHECK_DLC        0x0040
        #define RX_NO_AUTOTIMER     0x0080
        #define RX_ANNOUNCE_RESUME  0x0100
        #define TX_RESET_MULTI_IDX  0x0200
        #define RX_RTR_FRAME        0x0400
        #define CAN_FD_FRAME        0x0800

These BCM flags are used as part of the BCM header that has the aforementioned opcodes. The flags are set on the bcm_msg_head struct:

        struct bcm_msg_head {
            __u32 opcode;
            __u32 flags;
            __u32 count;
            struct bcm_timeval ival1, ival2;
            canid_t can_id;
            __u32 nframes;
            struct can_frame frames[0];
        };

The existing documentation for the BCM constants (https://docs.python.org/3/library/socket.html#socket.CAN_BCM) seems to imply that these constants should already be included, but they are not.

See the Linux headers for more details: https://elixir.bootlin.com/linux/latest/source/include/uapi/linux/can/bcm.h

[ambv]

New changeset 31c4fd2 by Łukasz Langa (karl ding) in branch 'master':
bpo-37085: Expose SocketCAN bcm_msg_head flags (bpo-13646)
31c4fd2

[miss-islington]

New changeset d8b914a by Miss Islington (bot) in branch '3.8':
bpo-37085: Expose SocketCAN bcm_msg_head flags (GH-13646)
d8b914a

[taleinat]

Karl, many thanks for bringing this up, making a PR and iterating on it with me!