[cfe-dev] [PATCH] [Driver] Add -ivfsoverlay-lib option to load VFS from shared library

[Andrew Savonichev via cfe-dev]

Hi Volodymyr,

I'm trying to setup a pre-processing of input files: input source file
contains a region, which is not a valid C code, but external tool can
consume it and replace it with meaningful code. This replacement may
have standard C preprocessor directives (e.g. #include), so the tool
should run before C preprocessor and follow #include directives,
preprocessing #included files as well.

With VFS this is pretty easy to do: you just implement a
FileSystem::openFileForRead function which returns a file after
pre-processing, and Clang calls this function whenever it needs a file.

In general, VFS is similar to Filesystem in Userspace (FUSE): it allows
you to read files from memory instead of a real file system, but it is
more portable than FUSE.

> Hello Andrew,
>
> That is an interesting idea with providing VFS as a shared
> library. Can you please provide more details about what you are trying
> to accomplish with custom VFS? It is hard to judge about merits of the
> approach without knowing the intended usage.
>
> Thanks,
> Volodymyr
>
>> On May 28, 2018, at 04:23, Andrew Savonichev via cfe-dev <cfe-dev at lists.llvm.org> wrote:
>>
>> Hi,
>>
>> Recently I was trying to hijack into clang's file management to do a
>> custom pre-processing of input files, and found that VirtualFileSystem
>> (VFS) is pretty flexible and can be extended to support any weird
>> use-cases related to files: preprocessing, in-memory files, code
>> generation, etc.
>>
>> Unfortunately, it is not exposed from clang driver, and you have to
>> patch clang to add your own custom VFS. Thus I added an option to clang
>> cc1 driver that loads a said shared library, gets a VFS and pushes it on
>> top of real file system.
>>
>> The patch is on the review: https://reviews.llvm.org/D47190
>>
>> Any commets/suggestions are welcome.
>>
>> --
>> Andrew

-- 
Andrew

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