Re: [PATCH bpf v2] lib/buildid: use __kernel_read() for sleepable context

[Matthew Wilcox]

On Thu, Dec 18, 2025 at 04:16:40PM -0800, Shakeel Butt wrote:
> On Thu, Dec 18, 2025 at 11:55:39PM +0000, Matthew Wilcox wrote:
> > On Thu, Dec 18, 2025 at 12:55:05PM -0800, Shakeel Butt wrote:
> > > +	do {
> > > +		ret = __kernel_read(r->file, buf, sz, &pos);
> > > +		if (ret <= 0) {
> > > +			r->err = ret ?: -EIO;
> > > +			return NULL;
> > > +		}
> > > +		buf += ret;
> > > +		sz -= ret;
> > > +	} while (sz > 0);
> > 
> > Why are you doing a loop around __kernel_read()?  eg kernel_read() does
> > not do a read around __kernel_read().  The callers of kernel_read()
> > don't do a loop either.  So what makes you think it needs to have a loop
> > around it?
> 
> I am assuming that __kernel_read() can return less data than the
> requested. Is that assumption incorrect?

I think it can, but I don't think a second call will get any more data.
For example, it could hit EOF.  What led you to think that calling it in
a loop was the right approach?