I got tired of debugging whether a server was advertising the correct things during negotiation by inspecting the trace logs of qemu-io as client - not to mention that without SOME sort of client tracing particular commands, we can't easily regression test the server for correct behavior. The final straw was at KVM Forum, when Nir asked me to make sure there was a way to easily determine if an NBD server is exposing what we really want (and fixing x-dirty-bitmap to behave saner fell out as a result of answering that question).
I note that upstream NBD has 'nbd-client -l $host' for querying just export names (with no quoting, so you have to know that a blank line means the default export), but it wasn't powerful enough, so I implemented 'qemu-nbd -L' to document everything. Upstream NBD has separate 'nbd-client' and 'nbd-server' binaries, while we only have 'qemu-nbd' (which is normally just a server, but 'qemu-nbd -c' also operates a second thread as a client). Our other uses of qemu as NBD client are for consuming a block device (as in qemu-io, qemu-img, or a drive to qemu) - but those binaries are less suited to something so specific to the NBD protocol. Bonus: As a result of my work on this series, nbdkit now supports NBD_OPT_INFO (my interoperability testing between server implementations has been paying off, both at fixing server bugs, and at making this code more reliable across difference in valid servers). Also available at: https://repo.or.cz/qemu/ericb.git qemu-nbd-list-v2 v1->v2: Lots of rework: several new patches added, several split into more managable pieces, a couple reordered. Use g_free consistently. Add R-b where the patch didn't change too much beyond the review. 001/22:[----] [--] 'qemu-nbd: Use program name in error messages' 002/22:[down] 'nbd: Document timeline of various features' 003/22:[down] 'maint: Allow for EXAMPLES in texi2pod' 004/22:[down] 'qemu-nbd: Enhance man page' 005/22:[0006] [FC] 'nbd/client: More consistent error messages' 006/22:[0009] [FC] 'qemu-nbd: Fail earlier for -c/-d on non-linux' 007/22:[down] 'qemu-nbd: Avoid strtol open-coding' 008/22:[0012] [FC] 'nbd/client: Drop pointless buf variable' 009/22:[0114] [FC] 'nbd/client: Refactor nbd_receive_list()' 010/22:[0006] [FC] 'nbd/client: Move export name into NBDExportInfo' 011/22:[down] 'nbd/client: Change signature of nbd_negotiate_simple_meta_context()' 012/22:[down] 'nbd/client: Improve error handling in nbd_negotiate_simple_meta_context()' 013/22:[down] 'nbd/client: Split out nbd_send_one_meta_context()' 014/22:[down] 'nbd/client: Split out nbd_receive_one_meta_context()' 015/22:[----] [-C] 'nbd/client: Refactor return of nbd_receive_negotiate()' 016/22:[0036] [FC] 'nbd/client: Split handshake into two functions' 017/22:[down] 'nbd/client: Pull out oldstyle size determination' 018/22:[0078] [FC] 'nbd/client: Add nbd_receive_export_list()' 019/22:[down] 'nbd/client: Add meta contexts to nbd_receive_export_list()' 020/22:[0034] [FC] 'qemu-nbd: Add --list option' 021/22:[0028] [FC] 'nbd/client: Work around 3.0 bug for listing meta contexts' 022/22:[0021] [FC] 'iotests: Enhance 223, 233 to cover 'qemu-nbd --list'' Eric Blake (22): qemu-nbd: Use program name in error messages nbd: Document timeline of various features maint: Allow for EXAMPLES in texi2pod qemu-nbd: Enhance man page nbd/client: More consistent error messages qemu-nbd: Fail earlier for -c/-d on non-linux qemu-nbd: Avoid strtol open-coding nbd/client: Drop pointless buf variable nbd/client: Refactor nbd_receive_list() nbd/client: Move export name into NBDExportInfo nbd/client: Change signature of nbd_negotiate_simple_meta_context() nbd/client: Improve error handling in nbd_negotiate_simple_meta_context() nbd/client: Split out nbd_send_one_meta_context() nbd/client: Split out nbd_receive_one_meta_context() nbd/client: Refactor return of nbd_receive_negotiate() nbd/client: Split handshake into two functions nbd/client: Pull out oldstyle size determination nbd/client: Add nbd_receive_export_list() nbd/client: Add meta contexts to nbd_receive_export_list() qemu-nbd: Add --list option nbd/client: Work around 3.0 bug for listing meta contexts iotests: Enhance 223, 233 to cover 'qemu-nbd --list' docs/interop/nbd.txt | 19 +- qemu-nbd.texi | 107 ++++- Makefile | 18 +- include/block/nbd.h | 27 +- nbd/nbd-internal.h | 3 +- block/nbd-client.c | 9 +- nbd/client.c | 796 +++++++++++++++++++++++++------------ qemu-nbd.c | 216 ++++++++-- nbd/trace-events | 11 +- scripts/texi2pod.pl | 2 +- tests/qemu-iotests/223 | 2 + tests/qemu-iotests/223.out | 20 + tests/qemu-iotests/233 | 19 +- tests/qemu-iotests/233.out | 17 +- 14 files changed, 918 insertions(+), 348 deletions(-) -- 2.17.2