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From:   Chuck Lever III <chuck.lever@oracle.com>
To:     Steven Rostedt <rostedt@goodmis.org>
CC:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        David Wysochanski <dwysocha@redhat.com>,
        Bruce Fields <bfields@fieldses.org>
Subject: Re: [PATCH v2 01/25] NFSD: Fix TP_printk() format specifier in
 trace_nfsd_dirent()
Thread-Topic: [PATCH v2 01/25] NFSD: Fix TP_printk() format specifier in
 trace_nfsd_dirent()
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Date:   Wed, 12 May 2021 16:52:05 +0000
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Hi Steve-

> On May 12, 2021, at 12:26 PM, Steven Rostedt <rostedt@goodmis.org> wrote:
>=20
> On Wed, 12 May 2021 11:35:02 -0400
> Chuck Lever <chuck.lever@oracle.com> wrote:
>=20
>> Since commit 9a6944fee68e ("tracing: Add a verifier to check string
>> pointers for trace events"), which was merged in v5.13-rc1,
>> TP_printk() no longer tacitly supports the "%.*s" format specifier.
>=20
> Hmm, this looks like a bug. I should allow the %.*s notation.
>=20
> I probably should fix that.

The underlying need is to support non-NUL-terminated C strings.

I assumed that since the commentary around 9a6944fee68e claims
the proper way to trace C strings is to use __string and friends,
and those do not support non-NUL-terminated strings, that such
strings are really not first-class citizens. Thus I concluded
that my use of '%.*s' was incorrect.

Having some __string-style helpers that can deal with such
strings would be valuable.


--
Chuck Lever