Re: [dpdk-dev] [PATCH] eal: fix detection of static or shared DPDK builds

[Bruce Richardson <bruce.richardson@intel.com>]

On Mon, Feb 08, 2021 at 04:33:19PM +0000, Bruce Richardson wrote:
> When checking the loading of EAL shared lib to see if we have a shared
> DPDK build, we only want to include part of the ABI version in the check
> rather than the whole thing. For example, with ABI version 21.1 for DPDK
> release 21.02, the linker links the binary against librte_eal.so.21,
> without the ".1".
> 
> To avoid any further brittleness in this area, we can check for multiple
> versions when doing the check, since just about any version of EAL implies
> a shared build. Therefore we check for presence of librte_eal.so with full
> ABI_VERSION extension, and then repeatedly remove the end part of the
> filename after the last dot, checking each time. For example (debug log
> output for static build):
> 
>   EAL: Checking presence of .so 'librte_eal.so.21.1'
>   EAL: Checking presence of .so 'librte_eal.so.21'
>   EAL: Checking presence of .so 'librte_eal.so'
>   EAL: Detected static linkage of DPDK
> 
> Fixes: 7781950f4d38 ("eal: fix shared lib mode detection")
> Cc: tredaelli@redhat.com
> Cc: stable@dpdk.org
> 
> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> ---

I saw this issue with OVS, where I was getting weird failures about ports
not being bound (in case of physical ports) or not being created (in case
of virtio ports), when using a shared build. Since it's potentially
serious, I'd appreciate if someone can reproduce the issue and verify the
fix so we can consider it for 21.02 inclusion.

To demonstrate this with regular DPDK, do a usual build of DPDK and then do
"ninja install" to install system-wide. Then build an example app, e.g.
l2fwd, using "make" from the examples/l2fwd directory. Running the example
normally, e.g. ./build/l2fwd -c F00, leads to no drivers being loaded or
ports being found. Adding "-d /path/to/drivers" e.g.
"/usr/local/lib/x86_64-linux-gnu/dpdk/pmds-21.1" on my system works as
expected. This shows the driver loading is not correct.

After applying this patch and re-running "ninja install", l2fwd should run
the same with and without the "-d" flag.

/Bruce