Re: [PATCH, RFC] shmat: introduce flag SHM_MAP_HINT

Andi Kleen
2008-10-06T19:29:23Z

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@linux.intel.com