What is the point of mincore() in reserve_area() in libs/wine/mmap.c?
trisk at opensolaris.org
Tue May 4 19:20:55 CDT 2010
On Tue, 04 May 2010 10:22:44 -0600, Charles Davis
<cdavis at 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)
>> &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.
> [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.
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
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