Messages in this thread | | | From | "Kamran Karimi" <> | Subject | Re: why VM_SHM has been removed from mm.h? | Date | Wed, 01 Mar 2006 08:58:39 -0600 |
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Thank you Hugh for the reply. Last time I used VM_SHM was in 2.2.x kernels. I have a programme called DIPC which makes System V shared memory segments (and also messages and semaphores) work over a network.
In the arch/xyz/mm/fault.c file, it checks the VM_SHM flag and then calls its logic. As a substitute I've been trying this ad-hoc code to see if a vma represents a Sys V shm:
file = vma->vm_file; if(file && (file->f_dentry) && (file->f_dentry->d_inode) && (id = file->f_dentry->d_inode->i_ino)) { shp = shm_lock(id); if(shp == NULL) return 0; // not a Sys V shm } else return 0; // not a Sys V shm
But the kernel hangs with an invalid-pointer error message. Any suggestions?
-Kamran
>On Tue, 28 Feb 2006, Kamran Karimi wrote: > > > > VM_SHM is used by DIPC to quickly recognise when we are dealing with a >System > > V IPC segment. It has been "removed" from recent kernels (set to 0). > >Curious: VM_SHM wasn't set on a System V IPC shm vma in any 2.4 or 2.6 >kernel that I know of; but was set on the vmas of a random collection >of drivers. Perhaps you've been using your own patch to set it on >SysV IPC shm vmas, and clear it from drivers' vmas? > >(We'll remove VM_SHM entirely once I've trawled through those drivers.) > > > Is there an easy way to find out if a segment is a Sys V shm? > >Nothing easy and reliable springs immediately to mind - from a VM point >of view, they're treated much the same as tmpfs files; but there >probably is some hacky way if we think about it long enough. > > > if not, I suggest we re-activate it. > >It seems that either you've been doing the wrong thing up to now, >and never noticed it; or that you've been using your own flag in >your own patch, and can continue to do so. No need for vanilla >kernel to reinstate VM_SHM. > >Are you sure you need to recognize them? > >Hugh
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