From sacadmin Fri Aug 25 13:36:50 2006 Received: from triplex.East.Sun.COM (triplex.East.Sun.COM [129.148.174.104]) by sac.sfbay.sun.com (8.13.6+Sun/8.13.6) with ESMTP id k7PKaoYf001881 for ; Fri, 25 Aug 2006 13:36:50 -0700 (PDT) Received: from triplex.East.Sun.COM (localhost [127.0.0.1]) by triplex.East.Sun.COM (8.13.8+Sun/8.13.8) with ESMTP id k7PKan4E013617; Fri, 25 Aug 2006 16:36:49 -0400 (EDT) Received: (from meem@localhost) by triplex.East.Sun.COM (8.13.8+Sun/8.13.8/Submit) id k7PKannX013614; Fri, 25 Aug 2006 16:36:49 -0400 (EDT) From: Peter Memishian MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <17647.24417.780670.4938@triplex.East.Sun.COM> Date: Fri, 25 Aug 2006 16:36:49 -0400 To: psarc@sac.sfbay.sun.com Cc: garrett@damore.org, garrett_damore@tadpole.com, Eric.Lowe@sun.com Subject: PSARC/2006/510 Kstat Constification X-Mailer: VM 7.17 under 21.4 (patch 18) "Social Property" XEmacs Lucid Status: RO Content-Length: 4057 I am sponsoring this case on behalf of Garrett D'Amore, from the OpenSolaris community (contributor agreement number #OS0034). Patch binding is requested. All interfaces remain at their existing stability levels. Since this case is quite straightforward, the timer is set for Wednesday, August 30th. *** NOTE: This case has "open" exposure, and will be visible to the *** *** OpenSolaris community. No confidential information, please! *** Problem ------- Currently, the interface used for device drivers wishing to export kernel statistics (kstats) uses a kernel API where a number of otherwise immutable strings are listed in the signature of routines as char * rather than const char *. Here are the relevant prototypes from : extern kstat_t *kstat_create(char *, int, char *, char *, uchar_t, uint_t, uchar_t); extern kstat_t *kstat_create_zone(char *, int, char *, char *, uchar_t, uint_t, uchar_t, zoneid_t); extern void kstat_set_string(char *, char *); extern void kstat_delete_byname(char *, int, char *); extern void kstat_delete_byname_zone(char *, int, char *, zoneid_t); extern void kstat_named_init(kstat_named_t *, char *, uchar_t); extern void kstat_timer_init(kstat_timer_t *, char *); Of these, only kstat_create() and kstat_named_init() are part of the Solaris DDI. In the future, other members of this list might be promoted to the Solaris DDI, but that is beyond the scope of this proposal. This leads to a few issues: 1. Developers may believe that the kstat framework may modify the strings. To work around that, developers may use inefficient solutions, like storing strings into temporary buffers before passing them to kstat. 2. Many developers use casting to work around this. For example, the return from ddi_driver_name() is often used as the first argument to kstat_create(). This is actually safe, because the kstat framework doesn't modify the string. But it is potentially unsafe because it assumes a promise that the kstat framework doesn't make. If it did modify the string, that would be very bad, because ddi_driver_name() returns a pointer to a string that is stored in other internal kernel structures. In general, casting to workaround problems like this indicates an API problem. 3. The use of non-constant strings may prevent the compiler from performing optimizations that it might otherwise be able to do, knowing that the data pointed to will not be modified. Proposed Solution ----------------- We propose to simply change the kernel API of the kstat framework so that immutable strings have a const attribute in the function signature. The resulting API thus becomes: extern kstat_t *kstat_create(const char *, int, const char *, const char *, uchar_t, uint_t, uchar_t); extern kstat_t *kstat_create_zone(const char *, int, const char *, const char *, uchar_t, uint_t, uchar_t, zoneid_t); extern void kstat_set_string(char *, const char *); extern void kstat_delete_byname(const char *, int, const char *); extern void kstat_delete_byname_zone(const char *, int, const char *, zoneid_t); extern void kstat_named_init(kstat_named_t *, const char *, uchar_t); extern void kstat_timer_init(kstat_timer_t *, const char *); This creates a 100% backwards compatible solution (both source and binary), as the compiler will happily promote non-const char * strings to const *, making it safe to pass either type of string. New code that takes advantage of this can dispense with an intermediate cast, and can directly use const char * values. (Code written thusly might not be portable to earlier versions of SunOS, but such a reverse backwards compatibility has never been guaranteed.) The online manual pages for kstat_create(9F) and kstat_named_init(9F) will be updated to reflect the change of these data types from char * to const char *. -- meem From sacadmin Wed Aug 30 17:20:22 2006 Received: from triplex.East.Sun.COM (triplex.East.Sun.COM [129.148.174.104]) by sac.sfbay.sun.com (8.13.6+Sun/8.13.6) with ESMTP id k7V0KLRx009904 for ; Wed, 30 Aug 2006 17:20:22 -0700 (PDT) Received: from triplex.East.Sun.COM (localhost [127.0.0.1]) by triplex.East.Sun.COM (8.13.8+Sun/8.13.8) with ESMTP id k7V0KKle009291; Wed, 30 Aug 2006 20:20:20 -0400 (EDT) Received: (from meem@localhost) by triplex.East.Sun.COM (8.13.8+Sun/8.13.8/Submit) id k7V0KKqD009288; Wed, 30 Aug 2006 20:20:20 -0400 (EDT) From: Peter Memishian MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <17654.11076.117573.540534@triplex.East.Sun.COM> Date: Wed, 30 Aug 2006 20:20:20 -0400 To: psarc@sac.sfbay.sun.com Cc: garrett@damore.org, garrett_damore@tadpole.com, Eric.Lowe@sun.com, meem@eng.Sun.COM Subject: Re: PSARC/2006/510 Kstat Constification X-Mailer: VM 7.17 under 21.4 (patch 18) "Social Property" XEmacs Lucid Status: RO Content-Length: 129 This case was approved at today's PSARC meeting. Garrett, Eric: will contact you separately regarding how to proceed. -- meem