Date: Mon, 22 Dec 2014 23:55:36 -0800 From: Rui Paulo <rpaulo@me.com> To: Andriy Gapon <avg@FreeBSD.org> Cc: Konstantin Belousov <kostikbel@gmail.com>, svn-src-head@FreeBSD.org, svn-src-all@FreeBSD.org, src-committers@FreeBSD.org, John Baldwin <jhb@FreeBSD.org> Subject: Re: svn commit: r276008 - in head/sys: kern sys Message-ID: <8F0C318C-9312-479E-BF1C-57E3654D6105@me.com> In-Reply-To: <549913D4.5090103@FreeBSD.org> References: <201412211332.sBLDW8VC030548@svn.freebsd.org> <201412220940.02509.jhb@freebsd.org> <08A2ABA0-C982-46BC-B309-3C23B8D277B9@me.com> <201412221417.42894.jhb@freebsd.org> <2C4635EF-6BE6-4ED7-B9D1-237F76259E88@me.com> <549913D4.5090103@FreeBSD.org>
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On Dec 22, 2014, at 23:03, Andriy Gapon <avg@FreeBSD.org> wrote: >=20 > On 23/12/2014 04:39, Rui Paulo wrote: >> On Dec 22, 2014, at 11:17, John Baldwin <jhb@freebsd.org> wrote: >>>=20 >>> On Monday, December 22, 2014 1:29:38 pm Rui Paulo wrote: >>>> On Dec 22, 2014, at 06:40, John Baldwin <jhb@freebsd.org> wrote: >>>>> Is there something specific to core dumps that makes vn_fullpath() = more >>>>> useful to have working before a process tries to open the core? = (As >>>>> compared to other newly-created files) >>>>=20 >>>> Yes: the ability to provide the full path to userland when a core = dump file=20 >>> is generated. >>>=20 >>> Can you be more specific? Are we printing the path on the console = after >>> destroying the generated path? Is it being written into a note in = the core >>> itself (but only having the vnode of the core file available and not = the=20 >>> generated path)? >>=20 >> No. I have some code that calls devctl_notify() when a core dump is = generated which is useful for running an automated debugging session. = We use this at work and I'll see if I can upstream it. What Konstantin = fixed was the generation of the cache entry in the corefile_open() = routine. This lets me call vn_fullpath() after vn_close() with a high = probability that it will work whereas, in the past, it was never in the = cache, so vn_fullpath() would always fail. >=20 > What is not entirely clear to me is why we need to recover the path = from the > vnode if we, obviously, have the path even before we have the vnode. Using the default setting for core files, it's based on the CWD of the = process. If you're using a different kern.corefile setting, it's = different. You will also need to account for the %N format string = (check the code for indexpos). Given that this is far from being a hot = path, it's much easier to just do a vn_fullpath() on the vnode than to = deal with all the other details.=20 -- Rui Paulo
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