On Tue, Apr 24, 2012 at 10:42:16AM +1200, Michael Kerrisk wrote: > 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. > Ok, here's a stab at manpage patch, let me know if I should send it as a separate patch. Thanks. -Jason diff --git a/man2/madvise.2 b/man2/madvise.2 index 36f988a..472c23a 100644 --- a/man2/madvise.2 +++ b/man2/madvise.2 @@ -247,6 +247,22 @@ Ensures that memory in the address range specified by and .IR length will not be collapsed into huge pages. +.TP +.BR MADV_DONTDUMP " (since Linux 3.4)" +Explicitly exclude from a core dump those pages in the range specified by +.I addr +and +.IR length . +Applications may have large areas of memory which are known not to be useful in +diagnosing a core dump. This specification takes precedence over the bit mask that +is set via the +.I /proc/PID/coredump_filter +file (see +.BR core (5)). +.TP +.BR MADV_DODUMP " (since Linux 3.4)" +Undo the effect of an earlier +.BR MADV_DONTDUMP. .SH "RETURN VALUE" On success .BR madvise () @@ -356,4 +372,5 @@ from the system call, as it should). .BR mmap (2), .BR mprotect (2), .BR msync (2), -.BR munmap (2) +.BR munmap (2), +.BR core (5) -- 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
