[WIP] Bindings for POSIX `stat` and `statvfs`

[MisterDA]

I'd like to have low-level ctypes bindings to stat, statfs, and statvfs. I'm not super familiar of how ctypes works, and I only have for now a macOS system (so, not POSIX), from which I've derived the constants, structures, and function prototypes. I hope I've somewhat cleared the path, and I would quite appreciate someone more experienced picking up the work. This patch doesn't build right now.

[toots]

That looks like a good start! The CI will tell you if it builds on ubuntu. You can also use a docker image to test your changes locally.

[MisterDA]

I've now used the definitions from POSIX sys/stat.h and sys/statvfs.h. Turns out statfs isn't in POSIX. I've removed Linux and macOS specific extensions (I've commented the code but I'll remove it later).

Two things still elude me: how to use Timespec.t (the ctypes type?) from posix-time2 in my ml and mli files, and how to expose the macros (typed mode_t -> int)

S_ISBLK(m)
    Test for a block special file.
S_ISCHR(m)
    Test for a character special file.
S_ISDIR(m)
    Test for a directory.
S_ISFIFO(m)
    Test for a pipe or FIFO special file.
S_ISREG(m)
    Test for a regular file.
S_ISLNK(m)
    Test for a symbolic link.
S_ISSOCK(m)
    Test for a socket. 

and these (typed ptr Stat.t -> int)

S_TYPEISMQ(buf)
    Test for a message queue.
S_TYPEISSEM(buf)
    Test for a semaphore.
S_TYPEISSHM(buf)
    Test for a shared memory object. 
S_TYPEISTMO(buf)
    Test macro for a typed memory object. 

[toots]

I've now used the definitions from POSIX sys/stat.h and sys/statvfs.h. Turns out statfs isn't in POSIX. I've removed Linux and macOS specific extensions (I've commented the code but I'll remove it later).

Two things still elude me: how to use Timespec.t (the ctypes type?) from posix-time2 in my ml and mli files, and how to expose the macros (typed mode_t -> int)

S_ISBLK(m)
    Test for a block special file.
S_ISCHR(m)
    Test for a character special file.
S_ISDIR(m)
    Test for a directory.
S_ISFIFO(m)
    Test for a pipe or FIFO special file.
S_ISREG(m)
    Test for a regular file.
S_ISLNK(m)
    Test for a symbolic link.
S_ISSOCK(m)
    Test for a socket. 

and these (typed ptr Stat.t -> int)

S_TYPEISMQ(buf)
    Test for a message queue.
S_TYPEISSEM(buf)
    Test for a semaphore.
S_TYPEISSHM(buf)
    Test for a shared memory object. 
S_TYPEISTMO(buf)
    Test macro for a typed memory object. 

Have you tried binding the macros like you would with a function? This could work. If not you can always define proper C function wrappers in the C header from the stubs generator.

As for the ctypes types, all the low-level libraries from the bindings should be available via sub-packages, for instance here:

(library
 (name posix_time2_types)
 (public_name posix-time2.types)
 (libraries posix-time2.constants posix-base ctypes.stubs))

[toots]

You might still be able to make the specific extension available BTW if you can make dune conditionally build them and reflect that in the opam package available clause.