Messages in this thread | | | Date | Fri, 4 Jul 2008 13:25:48 +0200 | From | Philippe De Muyter <> | Subject | Re: mmap'ed memory in core files ? |
| |
On Fri, Jul 04, 2008 at 08:33:14AM +0200, Stefan Richter wrote: > Hidehiro Kawai wrote: >> Philippe De Muyter wrote: >>> drivers/ieee1394/dma.c: >>> int dma_region_mmap(struct dma_region *dma, struct file *file, >>> struct vm_area_struct *vma) >>> { >>> [...] >>> vma->vm_ops = &dma_region_vm_ops; >>> vma->vm_private_data = dma; >>> vma->vm_file = file; >>> vma->vm_flags |= VM_RESERVED; >>> >>> return 0; >>> } >>> >>> So, actually the zone I would like to get dumped in the core file is >>> tagged >>> VM_RESERVED. >>> >>> I see the following ways to solve my problem : >>> - do not tag the zone as VM_RESERVED in ieee1394::dma_region_mmap >>> - tag the zone as VM_ALWAYSDUMP in ieee1394::dma_region_mmap >>> - add a bit in coredump_filter to dump the VM_RESERVED zones. >>> >>> As I don't know the real meaning of VM_RESERVED, I do not know which >>> choice >>> is the best one for the official kernel tree, > > I don't know these things either. But among else, VM_RESERVED prevents a > vma from being swapped out. Makes kind of sense, given that besides the > CPUs also the FireWire controller writes to this memory. > >>> but locally I'll go for >>> adding VM_ALWAYSDUMP in ieee1394::dma_region_mmap. >> I'm afraid I don't know real usages of VM_RESERVED and VM_IO, either. >> Allowing everyone to choose whether dump the dma region or not, >> perhaps we need to introduce a new VM flag (e.g. VM_DUMPABLE) and >> a coredump_filter bit which controls (VM_IO | VM_RESERVED) && >> VM_DUMPABLE area, for example. >> I think it is also OK to just add VM_ALWAYSDUMP flag to the dma >> region if the device driver knows the region is safely readable >> and small enough. > > It is safely readable. I don't know if it is small enough. The size of > the DMA buffer is AFAIK chosen by userspace (by the application program or > maybe a library) which uses the character device file ABIs for isochronous > FireWire IO of raw1394, video1394, or dv1394.
For video1394, the size of the buffer is N times the size of a frame, with N choosen by the application but small (let say < 32). The size of the frame depends on the camera. I have already worked with 8bpp 1600x1200 cameras,but with a smaller N in that case.
1600x1200x32 gives 60M. If they were allocated by malloc instead of by mmap, they would be dumped in the core files without any question about the size.
So I think we may consider the 'small enough' criteria is met.
Best regards
Philippe
| |