On Fri, Oct 02, 2020 at 09:27:09AM -0700, Linus Torvalds wrote: > On Thu, Oct 1, 2020 at 3:41 PM Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > > > > Better > > loff_t dummy = 0; > > ... > > wr = __kernel_write(file, data, bytes, &dummy); > > No, just fix __kernel_write() to work correctly. > > The fact is, NULL _is_ the right pointer for ppos these days. > > That commit by Christoph is buggy: it replaces new_sync_write() with a > buggy open-coded version. > > Notice how new_sync_write does > > kiocb.ki_pos = (ppos ? *ppos : 0); > ,,, > if (ret > 0 && ppos) > *ppos = kiocb.ki_pos; > > but the open-coded version doesn't. > > So just fix that in linux-next. The *last* thing we want is to have > different semantics for the "same" kernel functions. It's a bit unintuitive that ppos=NULL means "use pos 0", not "use file->f_pos". Anyway, it works. The important thing is, this is still broken in linux-next... - Eric
