Re: [PATCH v2] seq_file: Unconditionally use vmalloc for buffer

From: Al Viro
Date: Tue Mar 16 2021 - 08:53:07 EST

On Tue, Mar 16, 2021 at 08:24:50AM +0100, Greg Kroah-Hartman wrote:

> > Completely agreed. seq_get_buf() should be totally ripped out.
> > Unfortunately, this is going to be a long road because of sysfs's ATTR
> > stuff, there are something like 5000 callers, and the entire API was
> > designed to avoid refactoring all those callers from
> > sysfs_kf_seq_show().
> What is wrong with the sysfs ATTR stuff? That should make it so that we
> do not have to change any caller for any specific change like this, why
> can't sysfs or kernfs handle it automatically?

Hard to tell, since that would require _finding_ the sodding ->show()
instances first. Good luck with that, seeing that most of those appear
to come from templates-done-with-cpp...

AFAICS, Kees wants to protect against ->show() instances stomping beyond
the page size. What I don't get is what do you get from using seq_file
if you insist on doing raw access to the buffer rather than using
seq_printf() and friends. What's the point?