»Ø¸´: where does vmlist be initiated?

»Ø¸´: where does vmlist be initiated?

[Wang Yong]

-----Original Message-----
.c 1/4 thEE: Neil Booth <NeilB@earthling.net>
EO 1/4 thEE: Wang Yong <wung_y@263.net>
3-EI: Linux-MM <
EOAEU: 1999Ae8OA19EO 4:03
O/Ia: Re: where does vmlist be initiated?


>
>Hi Wang,
>
>There's only 3 lines that reference it in vmalloc.c, so it
>shouldn't be too hard to figure out, no?
>
>Neil.
>

Hi Neil,
  yes, vmlist does only referenced three times in vmalloc.c after it's
defined as NULL. These references are the only reference of vmlist
throughout the whole kernel. let's check them:

struct vm_struct * get_vm_area(unsigned long size)
{
...
 for (p = &vmlist; (tmp = *p) ; p = &tmp->next) {
  if (size + addr < (unsigned long) tmp->addr)
...
 }
}

void vfree(void * addr)
{
 for (p = &vmlist ; (tmp = *p) ; p = &tmp->next) {
...
 }
}

long vread(char *buf, char *addr, unsigned long count)
{
...
 for (tmp = vmlist; tmp; tmp = tmp->next) {
...
 }
}

i think these three functions will not be able to work if vmlist is null. do
you think so?


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Re: 指鹸 : where does vmlist be initiated?

[Neil Booth]

Wang Yong wrote:-
> 
> struct vm_struct * get_vm_area(unsigned long size)
> {
> ...
>  for (p = &vmlist; (tmp = *p) ; p = &tmp->next) {
>   if (size + addr < (unsigned long) tmp->addr)
> ...
>  }
> }

[SNIP]

> i think these three functions will not be able to work if vmlist is null. do
> you think so?

They must work as Linux boots.  The key is in the snippet I've kept above.
The test in

for (p = &vmlist; (tmp = *p) ; p = &tmp->next) {

is probably more clearly written as

(tmp = *p) != 0

which fails when vmlist is initially zero, so the loop never executes.
Note p does not hold the value of vmlist, but the address of vmlist.

vmlist is then initialised by the 

*p = area;

that comes a few lines later.

Neil.
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