On Tue, May 3, 2016 at 1:57 PM, Neil Horman <nhorman at tuxdriver.com> wrote: > On Tue, Apr 26, 2016 at 01:39:47PM -0400, Neil Horman wrote: >> Hey- >> So a few days ago we were reviewing Davids patch series to introduce >> the >> abiilty to dump hardware support from pmd DSO's in a human readable format. >> That effort encountered some problems, most notably the fact that stripping a >> DSO removed the required information that the proposed tool keyed off, as >> well >> as the need to dead reckon offsets between symbols that may not be constant >> (dependent on architecture). >> >> I was going to start looking into the possibility of creating a modinfo >> section in a simmilar fashion to what kernel modules do in linux or BSD. I >> decided to propose this solution instead though, because the kernel style >> solution requires a significant amount of infrastructure that I think we can >> maybe avoid maintaining, if we accept some minor caviats >> >> To do this We emit a set of well known marker symbols for each DSO that an >> external application can search for (in this case I called them >> this_pmd_driver<n>, where n is a counter macro). These marker symbols are >> n is a counter macro). These marker symbols are exported by PMDs for >> external access. External tools can then access these symbols via the >> dlopen/dlsym api (or via elfutils libraries) >> >> The symbols above alias the rte_driver struct for each PMD, and the external >> application can then interrogate the registered driver information. >> >> I also add a pointer to the pci id table struct for each PMD so that we can >> export hardware support. >> >> This approach has a few pros and cons: >> >> pros: >> 1) Its simple, and doesn't require extra infrastructure to implement. E.g. >> we >> don't need a new tool to extract driver information and emit the C code to >> build >> the binary data for the special section, nor do we need a custom linker >> script >> to link said special section in place >> >> 2) Its stable. Because the marker symbols are explicitly exported, this >> approach is resilient against stripping. >> >> cons: >> 1) It creates an artifact in that PMD_REGISTER_DRIVER has to be used in one >> compilation unit per DSO. As an example em and igb effectively merge two >> drivers into one DSO, and the uses of PMD_REGISTER_DRIVER occur in two >> separate >> C files for the same single linked DSO. Because of the use of the >> __COUNTER__ >> macro we get multiple definitions of the same marker symbols. >> >> I would make the argument that the downside of the above artifact isn't that >> big >> a deal. Traditionally in other projects a unit like a module (or DSO in our >> case) only ever codifies a single driver (e.g. module_init() in the linux >> kernel >> is only ever used once per built module). If we have code like igb/em that >> shares some core code, we should build the shared code to object files and >> link >> them twice, once to an em.so pmd and again to an igb.so pmd. >> >> But regardless, I thought I would propose this to see what you all thought of >> it. >> >> FWIW, heres sample output of the pmdinfo tool from this series probing the >> librte_pmd_ena.so module: >> >> [nhorman at hmsreliant dpdk]$ ./build/app/pmdinfo >> ~/git/dpdk/build/lib/librte_pmd_ena.so >> PMD 0 Information: >> Driver Name: ena_driver >> Driver Type: PCI >> |====================PCI Table========================| >> | VENDOR ID | DEVICE ID | SUBVENDOR ID | SUBDEVICE ID | >> |-----------------------------------------------------| >> | 1d0f| ec20| ffff| ffff| >> | 1d0f| ec21| ffff| ffff| >> |-----------------------------------------------------| >> >> >> >> > Ping, thoughts here?
- This implementation does not support binaries, so it is not suitable for people who don't want dso, this is partially why I used bfd rather than just dlopen. - The name of the tool "pmdinfo" is likely to cause problems, I would say we need to prefix t with dpdk. - How does it behave if we strip the dsos ? - Using __COUNTER__ seeems a bit tricky to me, can't this cause misalignments ? - The tool output format is not script friendly from my pov. -- David Marchand