03/08/2017 18:15, Stephen Hemminger: > On Thu, 3 Aug 2017 14:21:38 +0100 > Bruce Richardson <bruce.richard...@intel.com> wrote: > > > On Thu, Aug 03, 2017 at 01:21:35PM +0100, Chilikin, Andrey wrote: > > > To control some device-specific features public device-specific functions > > > rte_pmd_*.h are used. > > > > > > But this solution requires applications to distinguish devices at runtime > > > and, depending on the device type, call corresponding device-specific > > > functions even if functions' parameters are the same. > > > > > > IOCTL-like API can be added to ethdev instead of public device-specific > > > functions to address the following: > > > > > > * allow more usable support of features across a range of NIC from > > > one vendor, but not others > > > * allow features to be implemented by multiple NIC drivers without > > > relying on a critical mass to get the functionality in ethdev > > > * there are a large number of possible device specific functions, and > > > creating individual APIs for each one is not a good solution > > > * IOCTLs are a proven method for solving this problem in other areas, > > > i.e. OS kernels. > > > > > > Control requests for this API will be globally defined at ethdev level, so > > > an application will use single API call to control different devices from > > > one/multiple vendors. > > > > > > API call may look like as a classic ioctl with an extra parameter for > > > argument length for better sanity checks: > > > > > > int > > > rte_eth_dev_ioctl(uint16_t port, uint64_t ctl, void *argp, > > > unsigned arg_length); > > > > > > Regards, > > > Andrey > > > > I think we need to start putting in IOCTLs for ethdevs, much as I hate > > to admit it, since I dislike IOCTLs and other functions with opaque > > arguments! Having driver specific functions I don't think will scale > > well as each vendor tries to expose as much of their driver specific > > functionality as possible. > > > > One other additional example: I discovered just this week another issue > > with driver specific functions and testpmd, when I was working on the > > meson build rework. > > > > * With shared libraries, when we do "ninja install" we want our DPDK > > libs moved to e.g. /usr/local/lib, but the drivers moved to a separate > > driver folder, so that they can be automatically loaded from that > > single location by DPDK apps [== CONFIG_RTE_EAL_PMD_PATH]. > > * However, testpmd, as well as using the drivers as plugins, uses > > driver-specific functions, which means that it explicitly links > > against the pmd .so files. > > * Those driver .so files are not in with the other libraries, so ld.so > > does not find the pmd, and the installed testpmd fails to run due to > > missing library dependencies. > > * The workaround is to add the drivers path to the ld load path, but we > > should not require ld library path changes just to get DPDK apps to > > work. > > > > Using ioctls instead of driver-specific functions would solve this. > > > > My 2c. > > My 2c. No. > > Short answer: > Ioctl's were a bad idea in Unix (per Dennis Ritchie et al) and are now > despised by Linux kernel developers. They provide an unstructured, unsecured, > back door for device driver abuse. Try to get a new driver in Linux with > a unique ioctl, and it will be hard to get accepted. > > Long answer: > So far every device specific feature has fit into ethdev model. Doing ioctl > is admitting "it is too hard to be general, we need need an out". For > something > that is a flag, it should fit into existing config model; ignoring silly ABI > constraints. > For a real feature (think flow direction), we want a first class API for that. > For a wart, then devargs will do. > > Give a good example of something that should be an ioctl. Don't build the > API first and then let it get cluttered.
I agree with Stephen. And please do not forget that ioctl still requires an API: the argument that you put in ioctl is the API of the feature. So it is the same thing as defining a new function. The real debate is to decide if we want to continue adding more control path features in DPDK or focus on Rx/Tx. But this discussion would be better lead with some examples/requests.
