On Thu, Feb 20, 2020 at 07:50:39PM -0800, John Hubbard wrote:
> This tiny patch made me pause, because I wasn't sure at first of the exact
> intent of the lines above. Once I worked it out, it seemed like it might
> be helpful (or overkill??) to add a few hints for the reader, especially since
> there are no hints in the function's (minimal) documentation header. What
> do you think of this?
>
> /*
> * If we can't read *any* pages without going past the inodes's isize
> * limit, give up entirely:
> */
> if (index > end_index)
> return;
>
> /* Cap nr_to_read, in order to avoid overflowing the ULONG type: */
> if (index + nr_to_read < index)
> nr_to_read = ULONG_MAX - index + 1;
>
> /* Cap nr_to_read, to avoid reading past the inode's isize limit: */
> if (index + nr_to_read >= end_index)
> nr_to_read = end_index - index + 1;
A little verbose for my taste ... How about this?
end_index = (isize - 1) >> PAGE_SHIFT;
if (index > end_index)
return;
/* Avoid wrapping to the beginning of the file */
if (index + nr_to_read < index)
nr_to_read = ULONG_MAX - index + 1;
/* Don't read past the page containing the last byte of the file */
if (index + nr_to_read >= end_index)
nr_to_read = end_index - index + 1;
