On Tue, May 10, 2016 at 11:16:03AM +0100, Dr. David Alan Gilbert wrote: > * Dmitry V. Levin (l...@altlinux.org) wrote: > > On Fri, May 06, 2016 at 12:08:41PM +0100, Dr. David Alan Gilbert (git) > > wrote: [...] > > > + struct uffdio_api api_struct; > > > + /* With a bad fd */ > > > + memset(&api_struct, 0, sizeof(api_struct)); > > > + rc = ioctl(-1, UFFDIO_API, &api_struct); > > > > We have a function called tail_alloc: it allocates memory that ends on the > > page boundary; pages allocated by tail_alloc are preceded by an unmapped > > page and followed by another unmapped page. > > > > This method is used in many tests to check that strace parsers do not read > > beyond the end of structure they are supposed to parse, see e.g. > > tests/ioctl_v4l2.c. > > > > For example, > > (void) tail_alloc(1); /* initial memory hole just in case */ > > struct uffdio_api *api_struct = tail_alloc(sizeof(*api_struct)); > > memset(api_struct, 0, sizeof(*api_struct)); > > rc = ioctl(-1, UFFDIO_API, api_struct); > > OK, done. I'm not sure I understand the logic behind the tail_alloc(1)'s - > I've placed them at the start of each group.
I don't think the test really needs that many memory mapping holes, the first tail_alloc(1) is probably enough, but they won't harm. -- ldv
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