On 6/13/19 9:45 AM, Roman Stratiienko wrote: >> >> Just throw nbd-client in your initramfs. Every nbd server has it's own >> handshake protocol, embedding one particular servers handshake protocol into the >> kernel isn't the answer here. Thanks, The handshake protocol is well-specified: https://github.com/NetworkBlockDevice/nbd/blob/cdb0bc57f3faefd7a5562d57ad57cd990781c415/doc/proto.md All servers implement various subsets of that document for the handshake. > Also, as far as I know mainline nbd-server daemon have only 2 > handshake protocols. So called OLD-STYLE and NEW-STYLE. And OLD-STYLE > is no longer supported. So it should not be a problem, or please fix > me if I'm wrong. You are correct that oldstyle is no longer recommended. However, the current NBD specification states that newstyle has two different flavors, NBD_OPT_EXPORT_NAME (which you used, but is also old) and NBD_OPT_GO (which is newer, but is more likely to encounter differences where not all servers support it). The NBD specification includes a compatibility baseline: https://github.com/NetworkBlockDevice/nbd/blob/cdb0bc57f3faefd7a5562d57ad57cd990781c415/doc/proto.md#compatibility-and-interoperability and right now, NBD_OPT_GO (and _not_ NBD_OPT_EXPORT_NAME) is the preferred way forward. As long as your handshake implementation complies with the baseline documented there, you'll have maximum portability to the largest number of servers that also support the baseline - but not all servers are up to that baseline yet. So, this becomes a question of how much are you reinventing baseline portability handshake concerns in the kernel, vs. in initramfs. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
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