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From: Marcel Holtmann <marcel@holtmann.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Bluez mailing list <linux-bluetooth@vger.kernel.org>,
	y2038 Mailman List <y2038@lists.linaro.org>,
	Johan Hedberg <johan.hedberg@gmail.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Deepa Dinamani <deepa.kernel@gmail.com>,
	Rich Felker <dalias@libc.org>
Subject: Re: [RFC] y2038: HCI_TIME_STAMP with time64
Date: Fri, 10 Jan 2020 16:44:54 +0100	[thread overview]
Message-ID: <5E8DACB3-3B53-4E22-A834-4CEDFC6A1757@holtmann.org> (raw)
In-Reply-To: <CAK8P3a1mOzsaD+ZnN+ZKvmcan=K=KbnTjUOe1y8fS8WOMXT+Dw@mail.gmail.com>

Hi Arnd,

> I noticed earlier this week that the HCI_CMSG_TSTAMP/HCI_TIME_STAMP
> interface has no time64 equivalent, as we apparently missed that when
> converting the normal socket timestamps to support both time32 and time64
> variants of the sockopt and cmsg data.
> 
> The interface was originally added back in 2002 by Maksim Krasnyanskiy
> when bluetooth support first became non-experimental.
> 
> When using HCI_TIME_STAMP on a 32-bit system with a time64
> libc, users will interpret the { s32 tv_sec; s32 tv_usec } layout of
> the kernel as { s64 tv_sec; ... }, which puts complete garbage
> into the timestamp regardless of whether this code runs before or
> after y2038. From looking at codesearch.debian.org, I found two
> users of this: libpcap and hcidump. There are probably others that
> are not part of Debian.
> 
> Fixing this the same was as normal socket timestamps is not possible
> because include/net/bluetooth/hci.h is not an exported UAPI header.
> This means any changes to it for defining HCI_TIME_STAMP conditionally
> would be ignored by applications that use a different copy of the
> header.
> 
> I can see three possible ways forward:
> 
> 1. move include/net/bluetooth/hci.h to include/uapi/, add a conditional
>   definition of HCI_TIME_STAMP and make the kernel code support
>   both formats. Then change applications to rely on that version of
>   header file to get the correct definition but not change application code.
> 
> 2. Leave the kernel completely unchanged and modify only the users
>    to not expect the output to be a 'struct timeval' but interpret as
>    as { uint32_t tv_sec; int32_t tv_usec; } structure on 32-bit architectures,
>    which will work until the unsigned time overflows 86 years from now
>    in 2106 (same as the libpcap on-disk format).
> 
> 3. Add support for the normal SO_TIMESTAMPNS_NEW sockopt in
>   HCI, providing timestamps in the unambiguous { long long tv_sec;
>   long long tv_nsec; } format to user space, and change applications
>   to use that if supported by the kernel.

I have added SO_TIMESTAMP* to every Bluetooth socket a while back. And that should be used by the majority of the tools. One exception might by hcidump which has been replaced by btmon already anyway.

So I would not bother with HCI_TIME_STAMP fixing. We can do 2) if someone really still wants to use that socket option. However I am under the impression that 3) should be already possible.

Regards

Marcel


  reply	other threads:[~2020-01-10 15:44 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-10 10:11 [RFC] y2038: HCI_TIME_STAMP with time64 Arnd Bergmann
2020-01-10 15:44 ` Marcel Holtmann [this message]
2020-01-10 16:08   ` Arnd Bergmann
2020-01-10 17:52     ` Marcel Holtmann

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