Jason, On Thu, Mar 8, 2012 at 6:00 AM, Jason Baron <jbaron@xxxxxxxxxx> wrote: > Hi, > > The motivation for this change was that I was looking at a way for a qemu-kvm > process, to exclude the guest memory from its core dump, which can be quite > large. There are already a number of filter flags in > /proc/<pid>/coredump_filter, however, these allow one to specify 'types' of > kernel memory, not specific address ranges (which is needed in this case). > > Since there are no more vma flags available, the first patch eliminates the > need for the 'VM_ALWAYSDUMP' flag. The flag is used internally by the kernel to > mark vdso and vsyscall pages. However, it is simple enough to check if a vma > covers a vdso or vsyscall page without the need for this flag. > > The second patch then replaces the 'VM_ALWAYSDUMP' flag with a new > 'VM_DONTDUMP' flag, which can be set by userspace using new madvise flags: > 'MADV_DONTDUMP', and unset via 'MADV_DUMP'. The core dump filters continue to > work the same as before unless 'MADV_DONTDUMP' is set on the region. > > The qemu code which implements this features is at: > http://people.redhat.com/~jbaron/qemu-dump/qemu-dump.patch > > In my testing the qemu core dump shrunk from 383MB -> 13MB with this patch. > > I also believe that the 'MADV_DONTDUMP' flag might be useful for security > sensitive apps, which might want to select which areas are dumped. Since we have MADV_DODUMP MADV_DONTDUMP MADV_NODUMP heading for userspace in 3.4, would you be willing to write patches for the madvise(2) man page to describe these flags? See http://www.kernel.org/doc/man-pages/download.html for details on accessing man-pages Git. Cheers, Michael PS Please also CC linux-api@ when making API/ABI changes. -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Author of "The Linux Programming Interface", http://blog.man7.org/ -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
