From mboxrd@z Thu Jan 1 00:00:00 1970 From: Milian Wolff via lttng-dev Subject: Re: decoding tracef msg string via babeltrace API Date: Wed, 10 Apr 2019 10:57:35 +0200 Message-ID: <13178500.jIEOPmTTT8__46717.6245221467$1554886682$gmane$org@milian-kdab2> References: <33072915.QNGMzHgIAz@agathebauer> <2430999.6Ms1xt7J43@milian-kdab2> Reply-To: Milian Wolff Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============6137908555948221706==" Return-path: Received: from mail.kdab.com (mail.kdab.com [176.9.126.58]) by lists.lttng.org (Postfix) with ESMTPS id 44fJ2f0ZSXz1KQC for ; Wed, 10 Apr 2019 04:57:45 -0400 (EDT) In-Reply-To: <2430999.6Ms1xt7J43@milian-kdab2> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: lttng-dev-bounces@lists.lttng.org Sender: "lttng-dev" To: =?ISO-8859-1?Q?J=E9r=E9mie?= Galarneau Cc: "lttng-dev@lists.lttng.org" List-Id: lttng-dev@lists.lttng.org --===============6137908555948221706== Content-Type: multipart/signed; boundary="nextPart40919564.QW1g1hyK2F"; micalg="sha256"; protocol="application/pkcs7-signature" --nextPart40919564.QW1g1hyK2F Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="iso-8859-1" On Wednesday, April 10, 2019 9:56:43 AM CEST Milian Wolff wrote: > On Tuesday, April 9, 2019 7:02:06 PM CEST J=E9r=E9mie Galarneau wrote: > > On Tue, 9 Apr 2019 at 04:36, Milian Wolff wrote: > > > On Thursday, April 4, 2019 8:25:51 PM CEST J=E9r=E9mie Galarneau wrot= e: > > > > Hi Milian, > > > >=20 > > > > I have pushed a fix [1] in the stable-1.5 branch that addresses the > > > > issue you have encountered with using bt_ctf_get_field_list(). > > > > This makes it possible to consume a character sequence's content. > > > >=20 > > > > The commit message contains an example to show how to essentially > > > > perform what the 'ctf-text' format plug-in achieves by accessing the > > > > internal string field. > > > >=20 > > > > Let me know if that works for you and I'll release an updated versi= on > > > > of the 1.5 branch. > > >=20 > > > Thank you, I'll try that out in the next days! > > >=20 > > > But: why can't we make bt_ctf_get_string return the string for us? Why > > > do > > > we > > > need to reinvent the wheel in consumers of the babeltrace API? You po= int > > > out > >=20 > > Hi, > >=20 > > Strings, sequences and arrays are three different types in CTF. > >=20 > > bt_ctf_get_string() can only be used on CTF strings. In the babeltrace = 1.x > > API, those are expressed through 'bt_definition's that have a > > 'bt_declaration' > > of type CTF_TYPE_STRING. It is not a general-purpose accessor to get > > a field's content as a C-string. > >=20 > > Changing this in the 1.x release series goes against the design of the > > API (dedicated functions per definition type) and would, arguably, be an > > ABI breaking change. > >=20 > > As pointed out in the commit message, bt_ctf_get_char_array() is > > a convenience function to access a character-array's contents as > > a C-string. An equivalent function could be added for sequences. > >=20 > > Since you pointed-out a bug in the existing API, my priority was > > in fixing that bug which prevented users from accessing the sequences' > > contents at all in the "looks like a string" case. That fix can be > > back-ported into existing releases and made available in a point-releas= e. > >=20 > > Adding new APIs is an orthogonal concern. I'm not against a > > convenience function that does what you want; but it won't be > > shoe-horned into an existing one. >=20 > I see. I'll have to live with this, but note how the current situation is > far from perfect: >=20 > There's no way to figure out the exact version of babeltrace, neither at > compile nor at runtime. So any user of babeltrace will potentially crash > when calling bt_ctf_get_field_list to read a string-sequence. Additionally, the suggested approach of iterating over the individual chars= in=20 the sequence doesn't allow for a zero-copy approach as is done with=20 bt_ctf_get_char_array or bt_ctf_get_string. Both could be solved if a bt_ctf_get_string_sequence or similar would be=20 introduced. Would this be accepted upstream, if I create a pull request, or= is=20 1.5 frozen and no new API is allowed to be added? Thanks =2D-=20 Milian Wolff | milian.wolff@kdab.com | Senior Software Engineer KDAB (Deutschland) GmbH, a KDAB Group company Tel: +49-30-521325470 KDAB - The Qt, C++ and OpenGL Experts --nextPart40919564.QW1g1hyK2F Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCDEIw ggXmMIIDzqADAgECAhBqm+E4O/8ra58B1dm4p1JWMA0GCSqGSIb3DQEBDAUAMIGFMQswCQYDVQQG EwJHQjEbMBkGA1UECBMSR3JlYXRlciBNYW5jaGVzdGVyMRAwDgYDVQQHEwdTYWxmb3JkMRowGAYD VQQKExFDT01PRE8gQ0EgTGltaXRlZDErMCkGA1UEAxMiQ09NT0RPIFJTQSBDZXJ0aWZpY2F0aW9u IEF1dGhvcml0eTAeFw0xMzAxMTAwMDAwMDBaFw0yODAxMDkyMzU5NTlaMIGXMQswCQYDVQQGEwJH QjEbMBkGA1UECBMSR3JlYXRlciBNYW5jaGVzdGVyMRAwDgYDVQQHEwdTYWxmb3JkMRowGAYDVQQK ExFDT01PRE8gQ0EgTGltaXRlZDE9MDsGA1UEAxM0Q09NT0RPIFJTQSBDbGllbnQgQXV0aGVudGlj YXRpb24gYW5kIFNlY3VyZSBFbWFpbCBDQTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEB 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