Subject: Re: Wine & NetBSD?
To: Todd Vierling <email@example.com>
From: Bang Jun-Young <firstname.lastname@example.org>
Date: 11/21/2001 03:35:53
On Tue, Nov 20, 2001 at 11:23:00AM -0500, Todd Vierling wrote:
> The format of the call is as follows:
> pa=mmap(addr, len, prot, flags, fildes, off);
> When MAP_FIXED is set in the flags argument, the implementation is
> informed that the value of pa must be addr, exactly. If MAP_FIXED is set,
> mmap() may return MAP_FAILED and set errno to [EINVAL]. If a MAP_FIXED
> request is successful, the mapping established by mmap() replaces any
> previous mappings for the process' pages in the range [pa, pa + len).
> When MAP_FIXED is not set, the implementation uses addr in an unspecified
> manner to arrive at pa. The pa so chosen will be an area of the address
'unspecified' - we should be free to choose any address which is valid.
> space that the implementation deems suitable for a mapping of len bytes
> to the file. All implementations interpret an addr value of 0 as granting
> the implementation complete freedom in selecting pa, subject to
> constraints described below. A non-zero value of addr is taken to be a
> suggestion of a process address near which the mapping should be placed.
> When the implementation selects a value for pa, it never places a mapping
> at address 0, nor does it replace any extant mapping.
The patch 100% satisfies the above citation, and _does_ better
than the current implementation. Take a look at it again:
+ else if (addr == 0 ||
+ (addr >= round_page((vaddr_t)p->p_vmspace->vm_taddr) &&
+ addr < round_page((vaddr_t)p->p_vmspace->vm_daddr + MAXDSIZ)))
+ addr = round_page((vaddr_t)p->p_vmspace->vm_daddr + MAXDSIZ);
NetBSD mmap doesn't check if the first argument is 0, nor does it
allow mapping to be established at lower (valid) address:
- addr = MAX(addr, round_page((vaddr_t)p->p_vmspace->vm_daddr +
This can be rewritten as follows:
else if (addr < round_page((vaddr_t)p->p_vmspace->vm_daddr + MAXDSIZ)
addr = round_page((vaddr_t)p->p_vmspace->vm_daddr + MAXDSIZE);
Now it's clearer, isn't it?
> aCCOrding to this citation, NetBSD is 100% correct in its implementation of
> MAP_FIXED vs. non-MAP_FIXED.
Yes, but the patch is also correct. Which one would we choose?
Bang Jun-Young <email@example.com>