Re: [patch: mremap to fixed addressse] Re: (XFree86) mmap of /proc/XXX/mem

Egbert Eich (eich@hilbert.ikp.physik.tu-darmstadt.de)
Mon, 6 Dec 1999 10:38:48 +0100 (MET)

Ben LaHaise writes:
> 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

I haven't tested it but it may do the job! Now this has to go into
the libc, too. Is there any chance we might see this in the kernel
someday?

Egbert

>
> 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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