What is the point of mincore() in reserve_area() in libs/wine/mmap.c?

[Johann "Myrkraverk" Oskarsson]

Hi all,

In the Solaris/BSD implementation of reserve_area() in libs/wine/mmap.c there is

        for (i = 0; i < size; i += pagesize)
            if (mincore( (caddr_t)addr + i, pagesize, &vec ) != -1) break;

&vec is never used again in that function.  What is the point of mincore() ?

I'm looking at this in reference to bug 22033.


Johann

What is the point of mincore() in reserve_area() in libs/wine/mmap.c?

[Charles Davis]

On 5/4/10 10:17 AM, Johann "Myrkraverk" Oskarsson wrote:
> Hi all,
>
> In the Solaris/BSD implementation of reserve_area() in libs/wine/mmap.c there is
>
> for (i = 0; i < size; i += pagesize)
>             if (mincore( (caddr_t)addr + i, pagesize, &vec ) != -1) break;
>
> &vec is never used again in that function.  What is the point of mincore() ?
> It's trying to see if the address is valid. From the manpage:

RETURN VALUES
     Upon successful completion, a value of 0 is returned.  Otherwise,
     a value of -1 is returned and errno is set to indicate the error.

ERRORS
     [EINVAL]           addr is not a valid address for user mode.

     [EFAULT]           an error occurred trying to copy to the output
                        character array vec.

vec is to make sure it failed because the address was invalid, not
because it couldn't write the flags out.

Chip

[Albert Lee]

On Tue, 04 May 2010 10:22:44 -0600, Charles Davis
<cdavis(a)mymail.mines.edu> wrote:
> On 5/4/10 10:17 AM, Johann "Myrkraverk" Oskarsson wrote:
> > Hi all,
> >
> > In the Solaris/BSD implementation of reserve_area() in libs/wine/mmap.c
> > there is
> >
> > for (i = 0; i < size; i += pagesize)
> >             if (mincore( (caddr_t)addr + i, pagesize, &vec ) != -1)
> >             break;
> >
> > &vec is never used again in that function.  What is the point of
> > mincore() ?
> > It's trying to see if the address is valid. From the manpage:
>
> RETURN VALUES
>      Upon successful completion, a value of 0 is returned.  Otherwise,
>      a value of -1 is returned and errno is set to indicate the error.
>
> ERRORS
>      [EINVAL]           addr is not a valid address for user mode.
>
> [EFAULT]           an error occurred trying to copy to the output
>                         character array vec.
>
> vec is to make sure it failed because the address was invalid, not
> because it couldn't write the flags out.
>
> Chip

It's a clever, though stop-the-world expensive way to determine which
areas of the address space already have mappings present so MAP_FIXED can
be used without accidentally clobbering another mapping. The strategy
probably should be revisited for OpenSolaris since mmap now accepts an
address hint.

-Albert