linux-kernel - Re: [PATCH, RFC] shmat: introduce flag SHM_MAP

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Date:	Mon, 6 Oct 2008 21:29:23 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andi Kleen <andi@...stfloor.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH, RFC] shmat: introduce flag SHM_MAP_HINT

On Mon, Oct 06, 2008 at 05:37:59PM +0300, Kirill A. Shutemov wrote:
> It allows interpret attach address as a hint, not as exact address.

First you should also do a patch for the manpage and send to 
the manpage maintainer.


>  #define SHM_LOCK 	11
> diff --git a/ipc/shm.c b/ipc/shm.c
> index e77ec69..19462bb 100644
> --- a/ipc/shm.c
> +++ b/ipc/shm.c
> @@ -819,7 +819,7 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
>  	if (shmid < 0)
>  		goto out;
>  	else if ((addr = (ulong)shmaddr)) {
> -		if (addr & (SHMLBA-1)) {
> +		if (!(shmflg & SHM_MAP_HINT) && (addr & (SHMLBA-1))) {
>  			if (shmflg & SHM_RND)
>  				addr &= ~(SHMLBA-1);	   /* round down */
>  			else
> @@ -828,7 +828,7 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
>  #endif
>  					goto out;
>  		}
> -		flags = MAP_SHARED | MAP_FIXED;
> +		flags = (shmflg & SHM_MAP_HINT ? 0 : MAP_FIXED) | MAP_SHARED;


IMHO you need at least make the

   if (find_vma_intersection(current->mm, addr, addr + size))
                        goto invalid;

test above conditional too.

-Andi

-- 
ak@...ux.intel.com
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