illumos gate

Here is a part of the source code with three tunables:

299static uint_t nfs3_max_transfer_size_clts = 32 * 1024;
300static uint_t nfs3_max_transfer_size_cots = 1024 * 1024;
301static uint_t nfs3_max_transfer_size_rdma = 1024 * 1024;
302
303uint_t
304nfs3_tsize(struct knetconfig *knp)
305{
306
307    if (knp->knc_semantics == NC_TPI_COTS_ORD ||
308        knp->knc_semantics == NC_TPI_COTS)
309        return (nfs3_max_transfer_size_cots);
310    if (knp->knc_semantics == NC_TPI_RDMA)
311        return (nfs3_max_transfer_size_rdma);
312    return (nfs3_max_transfer_size_clts);
313}

And here is how the nfs3_tsize function is compiled in (in OpenIndiana) :

> nfs3_tsize::dis
nfs3_tsize:                     pushq  %rbp
nfs3_tsize+1:                   movq   %rsp,%rbp
nfs3_tsize+4:                   subq   $0x8,%rsp
nfs3_tsize+8:                   movq   %rdi,-0x8(%rbp)
nfs3_tsize+0xc:                 movl   (%rdi),%eax
nfs3_tsize+0xe:                 leal   -0x2(%rax),%ecx
nfs3_tsize+0x11:                cmpl   $0x1,%ecx
nfs3_tsize+0x14:                jbe    +0x12    <nfs3_tsize+0x28>
nfs3_tsize+0x16:                cmpl   $0x5,%eax
nfs3_tsize+0x19:                movl   $0x100000,%eax
nfs3_tsize+0x1e:                movl   $0x8000,%ecx
nfs3_tsize+0x23:                cmovl.ne %ecx,%eax
nfs3_tsize+0x26:                jmp    +0x5     <nfs3_tsize+0x2d>
nfs3_tsize+0x28:                movl   $0x100000,%eax
nfs3_tsize+0x2d:                leave  
nfs3_tsize+0x2e:                ret    
>

It means that the compiler treats all three tunables above as constants (and they are not changed in the nfs_common.c file). This is not what we want.

The reason for it is that tunables are missing the volatile keyword. In addition, because of bug #3718 in Sun CC, we are required to remove the static keyword from all tunables.

This bug aims to add the volatile keyword (and remove the static keyword) from all tunables documented in SOLTUNEPARAMREF (https://github.com/rmustacc/illumos-docbooks/tree/master/stage/docs/SOLTUNEPARAMREF)