net-tcp_bbr: v3: use correct 64-bit division [bbr-v3-upstream-prep-2024-02-19-01]

[ptpt52]

This commit addresses an issue with integer division on 32-bit system builds, which resulted in undefined symbol errors during the build process.

Errors observed:

arm:
ERROR: modpost: "__aeabi_uldivmod" [net/ipv4/tcp_bbr.ko] undefined! ERROR: modpost: "__aeabi_ldivmod" [net/ipv4/tcp_bbr.ko] undefined!

x86, mips, ppc:
ERROR: modpost: "__udivdi3" [net/ipv4/tcp_bbr.ko] undefined! ERROR: modpost: "__divdi3" [net/ipv4/tcp_bbr.ko] undefined!

The fix ensures proper 64-bit division on affected architectures.

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[nealcardwell]

Thanks for the patch! Let's try to converge with the upstream tcp_tso_autosize():
https://elixir.bootlin.com/linux/v6.10/source/net/ipv4/tcp_output.c#L2013

The motivation here: we will likely ultimately just switch BBR to using that. So instead of this patch, can you please change the declaration of the "bytes" variable from:

 u64 bytes;

to:

 unsigned long bytes;

I imagine that will fix it? If so, let's go with that.

Thanks!

[ptpt52]

@nealcardwell
updated.
tested build ok for mips.

This change addresses a build failure on 32-bit systems due to undefined division symbols:

arm:
ERROR: modpost: "__aeabi_uldivmod" [net/ipv4/tcp_bbr.ko] undefined!
ERROR: modpost: "__aeabi_ldivmod" [net/ipv4/tcp_bbr.ko] undefined!

x86, mips, ppc:
ERROR: modpost: "__udivdi3" [net/ipv4/tcp_bbr.ko] undefined!
ERROR: modpost: "__divdi3" [net/ipv4/tcp_bbr.ko] undefined!

Since `sk->sk_pacing_rate` is already an `unsigned long`, the `bytes` variable is
updated to `unsigned long` to resolve these division issues and ensure compatibility
across both 32-bit and 64-bit platforms.

[nealcardwell]

Hi. I just noticed this is proposing to add this commit to bbr-v3-upstream-prep-2024-02-19-01. Any reason you are proposing to use that branch instead of v3?

[ptpt52]

Hi. I just noticed this is proposing to add this commit to bbr-v3-upstream-prep-2024-02-19-01. Any reason you are proposing to use that branch instead of v3?

I happened to use the bbr-v3-upstream-prep-2024-02-19-01 branch, but there’s no specific reason for it. You can easily cherry-pick this commit onto the v3 branch, or would you prefer me to submit a new PR directly to v3?