linux-kernel - Re: [PATCH bpf v2] lib/buildid: use __kernel

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Message-ID: <aUjYNUNygZh87Yih@casper.infradead.org>
Date: Mon, 22 Dec 2025 05:33:41 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Shakeel Butt <shakeel.butt@...ux.dev>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	Shaurya Rane <ssrane_b23@...vjti.ac.in>,
	"Darrick J . Wong" <djwong@...nel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Meta kernel team <kernel-team@...a.com>, bpf@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	syzbot+09b7d050e4806540153d@...kaller.appspotmail.com,
	Christoph Hellwig <hch@....de>
Subject: Re: [PATCH bpf v2] lib/buildid: use __kernel_read() for sleepable
 context

On Fri, Dec 19, 2025 at 09:42:13AM -0800, Andrii Nakryiko wrote:
> From a user perspective, I'd very much appreciate it if I get exactly
> the requested amount of bytes from freader_fetch_sync(), so yeah,
> let's please keep the loop. It does seem that ret <= 0 handling is
> correct and should not result in an endless loop.

No, you don't understand.  If __kernel_read() doesn't get all the data in
one call, it's not there to get.  If a partial amount of data is useful
(I suspect not), we can return it, otherwise an error is the way to go.
The loop just betrays a lack of understanding of the VFS.