IB/core: extended command: an improved infrastructure for uverbs commands
Commit 400dbc96 ("IB/core: Infrastructure for extensible uverbs commands") added an infrastructure for extensible uverbs commands while later commit 436f2ad0 ("IB/core: Export ib_create/destroy_flow through uverbs") exported ib_create_flow()/ib_destroy_flow() functions using this new infrastructure. According to the commit 400dbc96, the purpose of this infrastructure is to support passing around provider (eg. hardware) specific buffers when userspace issue commands to the kernel, so that it would be possible to extend uverbs (eg. core) buffers independently from the provider buffers. But the new kernel command function prototypes were not modified to take advantage of this extension. This issue was exposed by Roland Dreier in a previous review[1]. So the following patch is an attempt to a revised extensible command infrastructure. This improved extensible command infrastructure distinguish between core (eg. legacy)'s command/response buffers from provider (eg. hardware)'s command/response buffers: each extended command implementing function is given a struct ib_udata to hold core (eg. uverbs) input and output buffers, and another struct ib_udata to hold the hw (eg. provider) input and output buffers. Having those buffers identified separately make it easier to increase one buffer to support extension without having to add some code to guess the exact size of each command/response parts: This should make the extended functions more reliable. Additionally, instead of relying on command identifier being greater than IB_USER_VERBS_CMD_THRESHOLD, the proposed infrastructure rely on unused bits in command field: on the 32 bits provided by command field, only 6 bits are really needed to encode the identifier of commands currently supported by the kernel. (Even using only 6 bits leaves room for about 23 new commands). So this patch makes use of some high order bits in command field to store flags, leaving enough room for more command identifiers than one will ever need (eg. 256). The new flags are used to specify if the command should be processed as an extended one or a legacy one. While designing the new command format, care was taken to make usage of flags itself extensible. Using high order bits of the commands field ensure that newer libibverbs on older kernel will properly fail when trying to call extended commands. On the other hand, older libibverbs on newer kernel will never be able to issue calls to extended commands. The extended command header includes the optional response pointer so that output buffer length and output buffer pointer are located together in the command, allowing proper parameters checking. This should make implementing functions easier and safer. Additionally the extended header ensure 64bits alignment, while making all sizes multiple of 8 bytes, extending the maximum buffer size: legacy extended Maximum command buffer: 256KBytes 1024KBytes (512KBytes + 512KBytes) Maximum response buffer: 256KBytes 1024KBytes (512KBytes + 512KBytes) For the purpose of doing proper buffer size accounting, the headers size are no more taken in account in "in_words". One of the odds of the current extensible infrastructure, reading twice the "legacy" command header, is fixed by removing the "legacy" command header from the extended command header: they are processed as two different parts of the command: memory is read once and information are not duplicated: it's making clear that's an extended command scheme and not a different command scheme. The proposed scheme will format input (command) and output (response) buffers this way: - command: legacy header + extended header + command data (core + hw): +----------------------------------------+ | flags | 00 00 | command | | in_words | out_words | +----------------------------------------+ | response | | response | | provider_in_words | provider_out_words | | padding | +----------------------------------------+ | | . <uverbs input> . . (in_words * 8) . | | +----------------------------------------+ | | . <provider input> . . (provider_in_words * 8) . | | +----------------------------------------+ - response, if present: +----------------------------------------+ | | . <uverbs output space> . . (out_words * 8) . | | +----------------------------------------+ | | . <provider output space> . . (provider_out_words * 8) . | | +----------------------------------------+ The overall design is to ensure that the extensible infrastructure is itself extensible while begin more reliable with more input and bound checking. Note: The unused field in the extended header would be perfect candidate to hold the command "comp_mask" (eg. bit field used to handle compatibility). This was suggested by Roland Dreier in a previous review[2]. But "comp_mask" field is likely to be present in the uverb input and/or provider input, likewise for the response, as noted by Matan Barak[3], so it doesn't make sense to put "comp_mask" in the header. [1]: http://marc.info/?i=CAL1RGDWxmM17W2o_era24A-TTDeKyoL6u3NRu_=t_dhV_ZA9MA@mail.gmail.com [2]: http://marc.info/?i=CAL1RGDXJtrc849M6_XNZT5xO1+ybKtLWGq6yg6LhoSsKpsmkYA@mail.gmail.com [3]: http://marc.info/?i=525C1149.6000701@mellanox.comSigned-off-by:Yann Droneaud <ydroneaud@opteya.com> Link: http://marc.info/?i=cover.1383773832.git.ydroneaud@opteya.com [ Convert "ret ? ret : 0" to the equivalent "ret". - Roland ] Signed-off-by:
Roland Dreier <roland@purestorage.com>
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