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Subject[patch: mremap to fixed addressse] Re: (XFree86) mmap of /proc/XXX/mem
On Mon, 6 Dec 1999, Egbert Eich wrote:

> mremap doesn't let you set an address like mmap with MAP_FIXED does.

Oh, so you need something like the following patch.

-ben

diff -ur clean/2.3.30pre6/include/linux/mman.h 2.3.30pre6/include/linux/mman.h
--- clean/2.3.30pre6/include/linux/mman.h Mon Oct 7 08:18:36 1996
+++ 2.3.30pre6/include/linux/mman.h Sun Dec 5 20:56:02 1999
@@ -4,5 +4,6 @@
#include <asm/mman.h>

#define MREMAP_MAYMOVE 1
+#define MREMAP_FIXED 2

#endif /* _LINUX_MMAN_H */
diff -ur clean/2.3.30pre6/mm/mremap.c 2.3.30pre6/mm/mremap.c
--- clean/2.3.30pre6/mm/mremap.c Sat Nov 20 13:09:05 1999
+++ 2.3.30pre6/mm/mremap.c Sun Dec 5 22:33:13 1999
@@ -124,15 +124,14 @@
}

static inline unsigned long move_vma(struct vm_area_struct * vma,
- unsigned long addr, unsigned long old_len, unsigned long new_len)
+ unsigned long addr, unsigned long old_len, unsigned long new_len,
+ unsigned long new_addr)
{
struct vm_area_struct * new_vma;

new_vma = kmem_cache_alloc(vm_area_cachep, SLAB_KERNEL);
if (new_vma) {
- unsigned long new_addr = get_unmapped_area(addr, new_len);
-
- if (new_addr && !move_page_tables(current->mm, new_addr, addr, old_len)) {
+ if (!move_page_tables(current->mm, new_addr, addr, old_len)) {
*new_vma = *vma;
new_vma->vm_start = new_addr;
new_vma->vm_end = new_addr+new_len;
@@ -163,20 +162,49 @@
/*
* Expand (or shrink) an existing mapping, potentially moving it at the
* same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
+ *
+ * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
+ * This option implies MREMAP_MAYMOVE.
*/
asmlinkage unsigned long sys_mremap(unsigned long addr,
unsigned long old_len, unsigned long new_len,
- unsigned long flags)
+ unsigned long flags, unsigned long new_addr)
{
struct vm_area_struct *vma;
unsigned long ret = -EINVAL;

down(&current->mm->mmap_sem);
+ if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
+ goto out;
+
if (addr & ~PAGE_MASK)
goto out;
+
old_len = PAGE_ALIGN(old_len);
new_len = PAGE_ALIGN(new_len);

+ /* new_addr is only valid if MREMAP_FIXED is specified */
+ if (flags & MREMAP_FIXED) {
+ if (new_addr & ~PAGE_MASK)
+ goto out;
+ if (!(flags & MREMAP_MAYMOVE))
+ goto out;
+
+ if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
+ goto out;
+
+ /* Check if the location we're moving into overlaps the
+ * old location at all, and fail if it does.
+ */
+ if ((new_addr <= addr) && (new_addr+new_len) > addr)
+ goto out;
+
+ if ((addr <= new_addr) && (addr+old_len) > new_addr)
+ goto out;
+
+ do_munmap(new_addr, new_len);
+ }
+
/*
* Always allow a shrinking remap: that just unmaps
* the unnecessary pages..
@@ -184,11 +212,12 @@
ret = addr;
if (old_len >= new_len) {
do_munmap(addr+new_len, old_len - new_len);
- goto out;
+ if (!(flags & MREMAP_FIXED) || (new_addr == addr))
+ goto out;
}

/*
- * Ok, we need to grow..
+ * Ok, we need to grow.. or relocate.
*/
ret = -EFAULT;
vma = find_vma(current->mm, addr);
@@ -214,8 +243,11 @@
!vm_enough_memory((new_len - old_len) >> PAGE_SHIFT))
goto out;

- /* old_len exactly to the end of the area.. */
+ /* old_len exactly to the end of the area..
+ * And we're not relocating the area.
+ */
if (old_len == vma->vm_end - addr &&
+ !((flags & MREMAP_FIXED) && (addr != new_addr)) &&
(old_len != new_len || !(flags & MREMAP_MAYMOVE))) {
unsigned long max_addr = TASK_SIZE;
if (vma->vm_next)
@@ -241,10 +273,15 @@
* We weren't able to just expand or shrink the area,
* we need to create a new one and move it..
*/
- if (flags & MREMAP_MAYMOVE)
- ret = move_vma(vma, addr, old_len, new_len);
- else
- ret = -ENOMEM;
+ ret = -ENOMEM;
+ if (flags & MREMAP_MAYMOVE) {
+ if (!(flags & MREMAP_FIXED)) {
+ new_addr = get_unmapped_area(addr, new_len);
+ if (!new_addr)
+ goto out;
+ }
+ ret = move_vma(vma, addr, old_len, new_len, new_addr);
+ }
out:
up(&current->mm->mmap_sem);
return ret;


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