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Allow non-page aligned file offset mmap's, providing that the system is

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allowed to choose the address, or that the MAP_FIXED address has the same
remainder when modulo PAGE_SIZE as the file offset.  Apparently this is
posix1003.1b specified behavior.  SVR4 and the other *BSD's allow it too.
It costs us nothing to support and means we don't get EINVAL on some mmap
code that works perfectly elsewhere.

Obtained from: NetBSD
This commit is contained in:
Peter Wemm 1997-08-30 18:50:06 +00:00
parent bc4534f4cc
commit 54f42e4ba0
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=28940
1 changed files with 47 additions and 23 deletions
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70
sys/vm/vm_mmap.c
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@ -38,7 +38,7 @@
* from: Utah $Hdr: vm_mmap.c 1.6 91/10/21$
*
* @(#)vm_mmap.c 8.4 (Berkeley) 1/12/94
* $Id: vm_mmap.c,v 1.65 1997/07/17 04:34:03 dyson Exp $
* $Id: vm_mmap.c,v 1.66 1997/08/25 22:15:25 bde Exp $
*/
/*
@ -132,6 +132,15 @@ ogetpagesize(p, uap, retval)
}
#endif /* COMPAT_43 || COMPAT_SUNOS */
/*
* Memory Map (mmap) system call. Note that the file offset
* and address are allowed to be NOT page aligned, though if
* the MAP_FIXED flag it set, both must have the same remainder
* modulo the PAGE_SIZE (POSIX 1003.1b). If the address is not
* page-aligned, the actual mapping starts at trunc_page(addr)
* and the return value is adjusted up by the page offset.
*/
#ifndef _SYS_SYSPROTO_H_
struct mmap_args {
caddr_t addr;
@ -158,33 +167,45 @@ mmap(p, uap, retval)
vm_prot_t prot, maxprot;
caddr_t handle;
int flags, error;
off_t pos;
addr = (vm_offset_t) uap->addr;
size = uap->len;
prot = uap->prot & VM_PROT_ALL;
flags = uap->flags;
/*
* Address (if FIXED) must be page aligned. Size is implicitly rounded
* to a page boundary.
*/
addr = (vm_offset_t) uap->addr;
if (((flags & MAP_FIXED) && (addr & PAGE_MASK)) ||
(ssize_t) uap->len < 0 || ((flags & MAP_ANON) && uap->fd != -1))
pos = uap->pos;
/* make sure mapping fits into numeric range etc */
if ((pos + size > (vm_offset_t)-PAGE_SIZE) ||
(ssize_t) uap->len < 0 ||
((flags & MAP_ANON) && uap->fd != -1))
return (EINVAL);
/*
* Round page if not already disallowed by above test
* XXX: Is there any point in the MAP_FIXED align requirement above?
* Align the file position to a page boundary,
* and save its page offset component.
*/
size = uap->len;
pageoff = (addr & PAGE_MASK);
addr -= pageoff;
size += pageoff;
size = (vm_size_t) round_page(size);
pageoff = (pos & PAGE_MASK);
pos -= pageoff;
/* Adjust size for rounding (on both ends). */
size += pageoff; /* low end... */
size = (vm_size_t) round_page(size); /* hi end */
/*
* Check for illegal addresses. Watch out for address wrap... Note
* that VM_*_ADDRESS are not constants due to casts (argh).
*/
if (flags & MAP_FIXED) {
/*
* The specified address must have the same remainder
* as the file offset taken modulo PAGE_SIZE, so it
* should be aligned after adjustment by pageoff.
*/
addr -= pageoff;
if (addr & PAGE_MASK)
return (EINVAL);
/* Address range must be all in user VM space. */
if (VM_MAXUSER_ADDRESS > 0 && addr + size > VM_MAXUSER_ADDRESS)
return (EINVAL);
#ifndef i386
@ -195,19 +216,23 @@ mmap(p, uap, retval)
return (EINVAL);
}
/*
* XXX if no hint provided for a non-fixed mapping place it after the
* end of the largest possible heap.
* XXX for non-fixed mappings where no hint is provided or
* the hint would fall in the potential heap space,
* place it after the end of the largest possible heap.
*
* There should really be a pmap call to determine a reasonable location.
* There should really be a pmap call to determine a reasonable
* location.
*/
if (addr == 0 && (flags & MAP_FIXED) == 0)
else if (addr < round_page(p->p_vmspace->vm_daddr + MAXDSIZ))
addr = round_page(p->p_vmspace->vm_daddr + MAXDSIZ);
if (flags & MAP_ANON) {
/*
* Mapping blank space is trivial.
*/
handle = NULL;
maxprot = VM_PROT_ALL;
pos = 0;
} else {
/*
* Mapping file, get fp for validation. Obtain vnode and make
@ -229,6 +254,7 @@ mmap(p, uap, retval)
handle = NULL;
maxprot = VM_PROT_ALL;
flags |= MAP_ANON;
pos = 0;
} else {
/*
* Ensure that file and memory protections are
@ -255,9 +281,9 @@ mmap(p, uap, retval)
}
}
error = vm_mmap(&p->p_vmspace->vm_map, &addr, size, prot, maxprot,
flags, handle, uap->pos);
flags, handle, pos);
if (error == 0)
*retval = (int) addr;
*retval = (int) (addr + pageoff);
return (error);
}
@ -432,8 +458,6 @@ munmap(p, uap, retval)
if (VM_MIN_ADDRESS > 0 && addr < VM_MIN_ADDRESS)
return (EINVAL);
#endif
if (addr + size < addr)
return (EINVAL);
map = &p->p_vmspace->vm_map;
/*
* Make sure entire range is allocated.