Versioning and loading libraries

[stephentoub]

As discussed in dotnet/coreclr#441, we are currently brittle with regards to our usage of dlopen, which requires that we provide the name of a library that includes version information. We need to figure out how we want to handle this, for the specific case discussed in dotnet/coreclr#441, for DllImports in general, and for anywhere else we may rely on loading arbitrary libraries.

[Tragetaschen]

FWIW, that's already a common grief for users of aspnet/KestrelHttpServer on Linux, so it would be great if this becomes a general solution that is available for all packages outside.

Usually, you use something like pkg-config to learn about the installed library version when building from source and calling the C-linker.

Mono uses <dllmap/> in global and application specific config files to translate between a library name on a DllImport and the versioned library name like libc -> libc.so.6. The global /etc/mono/config is distribution-specific and filled when mono is built for that distribution.

[akoeplinger]

As @Tragetaschen said, this is a common problem and Mono's solution to this is dllmap as described here.

While browsing the net, I found that Julia also has an interesting approach: they provide an api that internally reads the output of /sbin/ldconfig -p and creates a map of all the libraries, e.g.:

$ /sbin/ldconfig -p | grep libcrypto
    libcrypto.so.1.0.0 (libc6,x86-64) => /lib/x86_64-linux-gnu/libcrypto.so.1.0.0

... which means one can just call the wrapper function with the "simple" module name and get back the proper name incl. version.

[kangaroo]

The Julia approach seems particularly nice, I've never liked having to ship dllmaps, they're a pain and confusing for users.

[natemcmaster]

I also agree that dllMaps are ugly, but it would be good to have a general solution for per-platform library names.

Adding to Kestrel user's grief: trying to get Microsoft.Data.Sqlite to load native sqlite calls is pain because DllImportAttribute requires a constant library name. On Windows it's "sqlite3" and OS X and *nix it's "libsqlite3".

[bricelam]

Please, please, please build on all the great work of Mono.

[jeffschwMSFT]

dotnet/coreclr#19373

[swaroop-sridhar]

Closing this issue, the matter is tracked by dotnet/corefx#32015.