msghdr.msg_iovlen is inconsistently declared in gnu and musl

[praveen-pk]

While using socket API in cloud-hypervisor project, I noticed an inconsistency with msghdr struct between gnu and musl targets.

In gnu
msghdr.msg_iovlen is declared as size_t

libc/src/unix/linux_like/linux/gnu/mod.rs

Line 95 in 0488a83

pub msg_iovlen: ::size_t,

In musl
msghdr.msg_iovlen is declared as c_int

libc/src/unix/linux_like/linux/musl/b64/mod.rs

Line 98 in 0488a83

pub msg_iovlen: ::c_int,

cloud-hypervisor/cloud-hypervisor#4642 (comment) describes the error I encountered due to this inconsistency.

Is this expected? If not, could you please fix it?

[niluxv]

Hm, glibc seems to declare it as an integer too, see the glibc header source.
(The musl one is correct, see the musl header source.)

But changing it would be a breaking change I guess...

[workingjubilee]

The glibc type should be corrected to match the glibc definition, we can consider this for 0.3

[git-bruh]

The current declaration seems to be correct, the linux-specific socket.h header in glibc declares it as size_t: https://github.com/bminor/glibc/blob/b6e3898194bbae78910bbe9cd086937014961e45/sysdeps/unix/sysv/linux/bits/socket.h#L269

[niluxv]

My bad, I looked at the generic source 😞

[niluxv]

So I suppose this issue can be closed then?

[Amanieu]

See this musl commit for the background. Essentially, the glibc version matches the one used in the kernel. Musl uses a POSIX-ly correct variant, but then zero-fills the padding in the syscall wrapper before passing it on to the kernel.

It is hard to say what the correct approach is here.