On Thu, Dec 19, 2013 at 10:25:42AM +1000, Peter Hutterer wrote: > On Wed, Dec 18, 2013 at 04:05:37PM -0800, Dmitry Torokhov wrote: > > On Thu, Dec 19, 2013 at 09:55:04AM +1000, Peter Hutterer wrote: > > > On Wed, Dec 18, 2013 at 03:48:37PM -0800, Dmitry Torokhov wrote: > > > > On Thursday, December 19, 2013 09:40:09 AM Peter Hutterer wrote: > > > > > > + memset(&abs, 0, sizeof(abs)); > > > > > > + for (i = valid_cnt; i < cnt; ++i) > > > > > > + if (copy_to_user(&pinfo->info[i], &abs, sizeof(abs))) > > > > > > + return -EFAULT; > > > > > > + > > > > > > + return 0; > > > > > > > > > > why don't you return the number of valid copied axes to the user? > > > > > that seems better even than forcing the remainder to 0. > > > > > > > > Well, if your program messed up buffers that it faulted we do not know > > > > for sure if data that did not cause fault ended up where it should have > > > > or if it smashed something else. This condition I think should be > > > > signaled early. > > > > > > not 100% sure I understand but I wasn't proposing to remove the -EFAULT, i > > > was proposing to replace "return 0" with "return valid_cnt". > > > > I understand what you were saying. Now consider: your program supplied > > buffer that is actually smaller than what it said to the kernel. > > Depending on the exact placement we may or may not fault when we get > > pass the buffer boundary, most likely not. We are likely to fault when > > we go way past the buffer boundary and wracked process' memory. If we > > return -EFAULT the program will at least notice that something wrong. If > > we return count it will try to resubmit the remainder of operation and > > not even know that there was something very bad happening. > > > > IOW we should not treat fault condition as other partial read/write > > conditions. > > I'm still not sure we're talking about the same thing :)
Hmm, it appears you are right ;) > let me rephrase: why can't we use the behaviour bits_to_user() provides? > it limits the output to maxlen and returns that value (or -EFAULT), it's > only a small step from that to limit the output to min(maxbit, ABS_CNT2). OK, makes sense. -- Dmitry -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
