On Wed, 2018-02-14 at 13:12 -0800, Matthew Wilcox wrote: > On Wed, Feb 14, 2018 at 12:45:52PM -0800, Joe Perches wrote: > > On Wed, 2018-02-14 at 12:11 -0800, Matthew Wilcox wrote: > > > We have kvmalloc_array in order to safely allocate an array with a > > > number of elements specified by userspace (avoiding arithmetic overflow > > > leading to a buffer overrun). But it's fairly common to have a header > > > in front of that array (eg specifying the length of the array), so we > > > need a helper function for that situation. > > > > > > kvmalloc_ab_c() is the workhorse that does the calculation, but in spite > > > of our best efforts to name the arguments, it's really hard to remember > > > which order to put the arguments in. kvzalloc_struct() eliminates that > > > effort; you tell it about the struct you're allocating, and it puts the > > > arguments in the right order for you (and checks that the arguments > > > you've given are at least plausible). > > > > > > For comparison between the three schemes: > > > > > > sev = kvzalloc(sizeof(*sev) + sizeof(struct v4l2_kevent) * elems, > > > GFP_KERNEL); > > > sev = kvzalloc_ab_c(elems, sizeof(struct v4l2_kevent), sizeof(*sev), > > > GFP_KERNEL); > > > sev = kvzalloc_struct(sev, events, elems, GFP_KERNEL); > > > > Perhaps kv[zm]alloc_buf_and_array is better naming. > > I think that's actively misleading. The programmer isn't allocating a > buf, they're allocating a struct. kvzalloc_hdr_arr was the earlier name, > and that made some sense; they're allocating an array with a header. > But nobody thinks about it like that; they're allocating a structure > with a variably sized array at the end of it. > > If C macros had decent introspection, I'd like it to be: > > sev = kvzalloc_struct(elems, GFP_KERNEL); > > and have the macro examine the structure pointed to by 'sev', check > the last element was an array, calculate the size of the array element, > and call kvzalloc_ab_c. But we don't live in that world, so I have to > get the programmer to tell me the structure and the name of the last > element in it. Look at your patch 4 - dev_dax = kzalloc(sizeof(*dev_dax) + sizeof(*res) * count, GFP_KERNEL); + dev_dax = kvzalloc_struct(dev_dax, res, count, GFP_KERNEL); Here what is being allocated is exactly a struct and an array. And this doesn't compile either. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
