librbd: rbd_aio_write_with_crc32c store CRC32C with initial value -1 to match msgr2 validation

[baum]

librbd: rbd_aio_write_with_crc32c store CRC32C with initial value -1 to match msgr2 validation

Fix runtime error, using test command:

   sudo dd if=/dev/zero bs=32k of=/dev/nvme0n1 count=1

The error log:

2025-11-23T11:24:10.512+0000 7f30f4ec0640  1 --2- [v2:192.168.13.2:6802/3444906816,v1:192.168.13.2:6803/3444906816] >> 192.168.13.3:0/3916714748 conn(0x527d400 0x728f700 crc :-1 s=THROTTLE_DONE pgs=2038703 gs=2038723 cs=0 l=1 c_cookie=0 s_cookie=0 reconnecting=0 rev1=1 crypto rx=0 tx=0 comp rx=0 tx=0)._handle_read_frame_epilogue_main bad segment crc calculated=1136411986 expected=4294967295

msg2 validation (src/msg/async/frames_v2.cc:47):
Calls bufferlist::crc32c(-1) with initial value -1
uint32_t crc = segment_bl.crc32c(-1); // Uses initial value -1 (0xFFFFFFFF)

The cached CRC is stored with initial value 0, but msg2 calculates with initial value -1 (0xFFFFFFFF).

see #65901

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[idryomov]

This is exactly the kind of thing I had in mind when suggesting to add a test in #65901 (comment).

If we are going to implicitly assume msgr2 here, that should at least be mentioned in librbd.h file where the public API is defined.

[idryomov]

The cached CRC is stored with initial value 0, but msg2 calculates with initial value -1 (0xFFFFFFFF).

The bufferlist code should be able to take a CRC for one initial value and transform it into a CRC for another initial value without repeating the full calculation (i.e. efficiently, without even looking at the data buffer). This means that as long as the precomputed CRC a) isn't manipulated with beforehand and b) gets stored with the correct initial value, the fact that there is a difference between msgr1 and msgr2 should be transparent to the user (except for the computational overhead of possibly needing to adjust the precomputed CRC).

If we are going to implicitly assume msgr2 here, that should at least be mentioned in librbd.h file where the public API is defined.

So after taking a deeper look, I don't think msgr2 or anything about its internals is worth mentioning there. We just need to clearly state what initial value is expected (or consider accepting it as a separate argument to be as flexible as possible).

[idryomov]

jenkins test make check

[idryomov]

jenkins test make check