Expose `len8_dlc` field of `can_frame` struct. #3357

de-vri-es · 2023-09-19T21:48:41Z

The can_frame struct on Linux has a len8_dlc field which can be used to stuff a few extra bits in the dlc field of the actual CAN frame on the wire (only allowed when the data length itself is 8, and if the hardware CAN controller allows it).

However, that field is not currently exposed. This PR exposes it as pub len8_dlc: u8 so we can get those extra 2.8 bits from our CAN frames 😅

It would have been nice to name the current can_dlc field as len, instead of the old deprecated name, but I guess that ship has sailed.

Upstream documentation: https://www.kernel.org/doc/html/latest/networking/can.html#how-to-use-socketcan

struct can_frame {
        canid_t can_id;  /* 32 bit CAN_ID + EFF/RTR/ERR flags */
        union {
                /* CAN frame payload length in byte (0 .. CAN_MAX_DLEN)
                 * was previously named can_dlc so we need to carry that
                 * name for legacy support
                 */
                __u8 len;
                __u8 can_dlc; /* deprecated */
        };
        __u8    __pad;   /* padding */
        __u8    __res0;  /* reserved / padding */
        __u8    len8_dlc; /* optional DLC for 8 byte payload length (9 .. 15) */
        __u8    data[8] __attribute__((aligned(8)));
};

Remark: The len element contains the payload length in bytes and should be used instead of can_dlc. The deprecated can_dlc was misleadingly named as it always contained the plain payload length in bytes and not the so called 'data length code' (DLC).

To pass the raw DLC from/to a Classical CAN network device the len8_dlc element can contain values 9 .. 15 when the len element is 8 (the real payload length for all DLC values greater or equal to 8).

rustbot · 2023-09-19T21:48:45Z

r? @JohnTitor

(rustbot has picked a reviewer for you, use r? to override)

JohnTitor · 2023-09-21T18:27:42Z

@bors r+

bors · 2023-09-21T18:27:44Z

📌 Commit 85dbb12 has been approved by JohnTitor

It is now in the queue for this repository.

bors · 2023-09-21T22:32:32Z

⌛ Testing commit 85dbb12 with merge 5c5c419...

Expose `len8_dlc` field of `can_frame` struct. The `can_frame` struct on Linux has a `len8_dlc` field which can be used to stuff a few extra bits in the `dlc` field of the actual CAN frame on the wire (only allowed when the data length itself is 8, and if the hardware CAN controller allows it). However, that field is not currently exposed. This PR exposes it as `pub len8_dlc: u8` so we can get those extra 2.8 bits from our CAN frames 😅 It would have been nice to name the current `can_dlc` field as `len`, instead of the old deprecated name, but I guess that ship has sailed. Upstream documentation: https://www.kernel.org/doc/html/latest/networking/can.html#how-to-use-socketcan > ```c > struct can_frame { > canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */ > union { > /* CAN frame payload length in byte (0 .. CAN_MAX_DLEN) > * was previously named can_dlc so we need to carry that > * name for legacy support > */ > __u8 len; > __u8 can_dlc; /* deprecated */ > }; > __u8 __pad; /* padding */ > __u8 __res0; /* reserved / padding */ > __u8 len8_dlc; /* optional DLC for 8 byte payload length (9 .. 15) */ > __u8 data[8] __attribute__((aligned(8))); > }; > ``` > > Remark: The len element contains the payload length in bytes and should be used instead of can_dlc. The deprecated can_dlc was misleadingly named as it always contained the plain payload length in bytes and not the so called 'data length code' (DLC). > > To pass the raw DLC from/to a Classical CAN network device the len8_dlc element can contain values 9 .. 15 when the len element is 8 (the real payload length for all DLC values greater or equal to 8).

bors · 2023-09-21T22:45:12Z

💔 Test failed - checks-actions

de-vri-es · 2023-09-25T07:22:18Z

I don't see any reason for the failure. Is it correct to assume that this was an unrelated CI failure? :o

JohnTitor · 2023-09-29T19:38:30Z

The failure is related. I think mips doesn't have it or our musl header is too old.

de-vri-es · 2023-09-30T08:51:28Z

Oh, sorry, the link just pointed to a job running "exit 1" and I didn't notice the other red check.

de-vri-es · 2023-09-30T09:33:00Z

Note that the can_frame struct comes from a Linux header, not from a glibc or musl header. I'm also pretty sure that mips has it too, but the headers are pulled in from the openwrt sdk which includes headers from linux 4.14, and the len8_dlc field was added in Linux commit ea7800565a128 which was released in 5.11.

What would be a good way forward for me to unblock this? Find a different linux mips distro with a newer kernel?

/edit: This openwrt release would fit the bill: https://downloads.openwrt.org/releases/23.05.0-rc4/targets/bcm47xx/generic/openwrt-sdk-23.05.0-rc4-bcm47xx-generic_gcc-12.3.0_musl.Linux-x86_64.tar.xz

de-vri-es · 2023-09-30T10:25:48Z

Hmm, updating to https://downloads.openwrt.org/releases/23.05.0-rc4/targets/bcm47xx/generic/openwrt-sdk-23.05.0-rc4-bcm47xx-generic_gcc-12.3.0_musl.Linux-x86_64.tar.xz breaks other tests, atleast if I locally run ci/run-docker.sh mipsel-unknown-linux-musl.

I guess I need to figure out why first :(

bors · 2023-11-11T22:21:02Z

☔ The latest upstream changes (presumably #3429) made this pull request unmergeable. Please resolve the merge conflicts.

tgross35 · 2024-11-20T00:46:31Z

@de-vri-es any chance you could update this? MIPS dropped to tier3 so if that was the cause of failure here, it shouldn't be a problem anymore.

de-vri-es · 2024-11-20T13:31:12Z

Re-applied the changes to current main.

de-vri-es · 2024-11-20T14:13:38Z

CI now fails because the kernel headers for the musl tests are taken from https://github.com/sabotage-linux/kernel-headers which is based on linux 4.19, but this field was introduced in linux 5.11 (released in february 2021).

tgross35 · 2024-11-20T17:28:49Z

Could you just update skip_field in libc-test/build.rs and leave a FIXME(musl)? We should be updating these in the near future

de-vri-es · 2024-11-25T10:58:35Z

Done, and rebased again!

@rustbot ready

de-vri-es · 2024-11-25T11:01:03Z

Huh.. I don't see my changes to build.rs anymore in the git history but CI succeeded.. Maybe I messed up the rebase and someone updated the musl headers in the mean time? 😆

tgross35

Thanks!

tgross35 · 2024-11-25T11:02:51Z

src/unix/linux_like/linux/mod.rs

@@ -1583,7 +1583,7 @@ s_no_extra_traits! {
        pub can_dlc: u8,


While you're here, mind adding a comment // FIXME(1.0): this field was renamed to `can_len` based on the docs?

tgross35 · 2024-11-25T11:04:49Z

Huh.. I don't see my changes to build.rs anymore in the git history but CI succeeded.. Maybe I messed up the rebase and someone updated the musl headers in the mean time? 😆

Indeed :) since #3921 musl is on 6.6

I left one quick unrelated request since you're updating the struct, should be ready in either case.

de-vri-es · 2024-11-25T11:07:16Z

Indeed :) since #3921 musl is on 6.6

Nice :)

I left one quick unrelated request since you're updating the struct, should be ready in either case.

Added the comment to can_dlc (new name is "len") :)

tgross35 · 2024-11-25T11:07:48Z

Oops thanks for the name correction. LGTM!

de-vri-es · 2024-11-25T11:09:16Z

Had to force-push again, I had a typo in FIXME.

(backport <rust-lang#3357>) (cherry picked from commit 48bdb18)

de-vri-es · 2024-11-25T13:10:16Z

@tgross35: Thanks for the reviews!

rustbot assigned JohnTitor Sep 19, 2023

rustbot added the S-waiting-on-review label Sep 19, 2023

de-vri-es changed the title ~~Expose len8_dlc field of can_frame struct.~~ Expose len8_dlc field of can_frame struct. Sep 19, 2023

JohnTitor approved these changes Sep 21, 2023

View reviewed changes

bors added S-waiting-on-bors and removed S-waiting-on-review labels Sep 21, 2023

bors added S-waiting-on-review and removed S-waiting-on-bors labels Sep 21, 2023

de-vri-es force-pushed the can-frame-len8-dlc branch from 85dbb12 to 1f88773 Compare September 27, 2023 17:47

JohnTitor added S-waiting-on-author and removed S-waiting-on-review labels Oct 9, 2023

de-vri-es force-pushed the can-frame-len8-dlc branch from 68c9234 to dba870b Compare November 20, 2024 13:30

rustbot added O-linux O-unix labels Nov 20, 2024

de-vri-es force-pushed the can-frame-len8-dlc branch 2 times, most recently from f1e04fc to 987fd8d Compare November 25, 2024 09:11

rustbot added S-waiting-on-review and removed S-waiting-on-author labels Nov 25, 2024

tgross35 approved these changes Nov 25, 2024

View reviewed changes

tgross35 reviewed Nov 25, 2024

View reviewed changes

tgross35 added the stable-nominated This PR should be considered for cherry-pick to libc's stable release branch label Nov 25, 2024

tgross35 added the S-waiting-on-ci label Nov 25, 2024

de-vri-es force-pushed the can-frame-len8-dlc branch from 987fd8d to cf2028b Compare November 25, 2024 11:05

tgross35 enabled auto-merge November 25, 2024 11:07

Expose len8_dlc field of can_frame struct on Linux

48bdb18

auto-merge was automatically disabled November 25, 2024 11:08
Head branch was pushed to by a user without write access

de-vri-es force-pushed the can-frame-len8-dlc branch from cf2028b to 48bdb18 Compare November 25, 2024 11:08

tgross35 enabled auto-merge November 25, 2024 11:09

tgross35 pushed a commit to tgross35/rust-libc that referenced this pull request Nov 25, 2024

Expose len8_dlc field of can_frame struct on Linux

ceeb0fe

(backport <rust-lang#3357>) (cherry picked from commit 48bdb18)

tgross35 mentioned this pull request Nov 25, 2024

[0.2]: Expose len8_dlc field of can_frame struct. #4143

Merged

tgross35 added this pull request to the merge queue Nov 25, 2024

Merged via the queue into rust-lang:main with commit 951cab5 Nov 25, 2024
45 checks passed

tgross35 added stable-applied This PR has been cherry-picked to libc's stable release branch and removed stable-nominated This PR should be considered for cherry-pick to libc's stable release branch labels Nov 25, 2024

andrewdavidmackenzie mentioned this pull request Nov 26, 2024

Bump libc from 0.2.164 to 0.2.165 andrewdavidmackenzie/pigg#667

Closed

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Expose `len8_dlc` field of `can_frame` struct. #3357

Expose `len8_dlc` field of `can_frame` struct. #3357

de-vri-es commented Sep 19, 2023 •

edited

Loading

rustbot commented Sep 19, 2023

JohnTitor commented Sep 21, 2023

bors commented Sep 21, 2023

bors commented Sep 21, 2023

bors commented Sep 21, 2023

de-vri-es commented Sep 25, 2023

JohnTitor commented Sep 29, 2023

de-vri-es commented Sep 30, 2023

de-vri-es commented Sep 30, 2023 •

edited

Loading

de-vri-es commented Sep 30, 2023

bors commented Nov 11, 2023

tgross35 commented Nov 20, 2024

de-vri-es commented Nov 20, 2024

de-vri-es commented Nov 20, 2024

tgross35 commented Nov 20, 2024

de-vri-es commented Nov 25, 2024

de-vri-es commented Nov 25, 2024

tgross35 left a comment

tgross35 Nov 25, 2024

de-vri-es Nov 25, 2024

de-vri-es Nov 25, 2024

tgross35 commented Nov 25, 2024

de-vri-es commented Nov 25, 2024

tgross35 commented Nov 25, 2024

de-vri-es commented Nov 25, 2024

de-vri-es commented Nov 25, 2024

Expose len8_dlc field of can_frame struct. #3357

Expose len8_dlc field of can_frame struct. #3357

Conversation

de-vri-es commented Sep 19, 2023 • edited Loading

rustbot commented Sep 19, 2023

JohnTitor commented Sep 21, 2023

bors commented Sep 21, 2023

bors commented Sep 21, 2023

bors commented Sep 21, 2023

de-vri-es commented Sep 25, 2023

JohnTitor commented Sep 29, 2023

de-vri-es commented Sep 30, 2023

de-vri-es commented Sep 30, 2023 • edited Loading

de-vri-es commented Sep 30, 2023

bors commented Nov 11, 2023

tgross35 commented Nov 20, 2024

de-vri-es commented Nov 20, 2024

de-vri-es commented Nov 20, 2024

tgross35 commented Nov 20, 2024

de-vri-es commented Nov 25, 2024

de-vri-es commented Nov 25, 2024

tgross35 left a comment

Choose a reason for hiding this comment

tgross35 Nov 25, 2024

Choose a reason for hiding this comment

de-vri-es Nov 25, 2024

Choose a reason for hiding this comment

de-vri-es Nov 25, 2024

Choose a reason for hiding this comment

tgross35 commented Nov 25, 2024

de-vri-es commented Nov 25, 2024

tgross35 commented Nov 25, 2024

de-vri-es commented Nov 25, 2024

de-vri-es commented Nov 25, 2024

Expose `len8_dlc` field of `can_frame` struct. #3357

Expose `len8_dlc` field of `can_frame` struct. #3357

de-vri-es commented Sep 19, 2023 •

edited

Loading

de-vri-es commented Sep 30, 2023 •

edited

Loading