From owner-freebsd-current@freebsd.org Tue Dec 8 19:13:35 2015 Return-Path: Delivered-To: freebsd-current@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 2BBC89D45B0; Tue, 8 Dec 2015 19:13:35 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 9FA9A1C9C; Tue, 8 Dec 2015 19:13:34 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kostik@localhost [127.0.0.1]) by kib.kiev.ua (8.15.2/8.15.2) with ESMTPS id tB8JDORI045632 (version=TLSv1 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO); Tue, 8 Dec 2015 21:13:24 +0200 (EET) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua tB8JDORI045632 Received: (from kostik@localhost) by tom.home (8.15.2/8.15.2/Submit) id tB8JDOYr045631; Tue, 8 Dec 2015 21:13:24 +0200 (EET) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Tue, 8 Dec 2015 21:13:24 +0200 From: Konstantin Belousov To: Dag-Erling Sm??rgrav Cc: Kirk McKusick , Maxim Sobolev , freebsd-current@freebsd.org, freebsd-hackers@freebsd.org Subject: Re: posix_fallocate(2) && posix_fadvise(2) are somewhat broken Message-ID: <20151208191324.GF82577@kib.kiev.ua> References: <868u55rl96.fsf@desk.des.no> <20151208174259.GA82577@kib.kiev.ua> <86poygrctt.fsf@desk.des.no> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <86poygrctt.fsf@desk.des.no> User-Agent: Mutt/1.5.24 (2015-08-30) X-Spam-Status: No, score=-2.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FREEMAIL_FROM,NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.1 X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on tom.home X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 08 Dec 2015 19:13:35 -0000 On Tue, Dec 08, 2015 at 07:54:06PM +0100, Dag-Erling Sm??rgrav wrote: > Konstantin Belousov writes: > > Dag-Erling Sm??rgrav writes: > > > Maxim Sobolev writes: > > > > Hi, while working on some unrelated feature I've noticed that at least > > > > those two system calls are not returning proper value (-1) on error. > > > > Instead actual errno value is returned from the syscall verbatim, > > > > i.e. posix_fadvise() returns 22 on EINVAL. > > > That's how syscalls work. > > No, this is not how typical syscalls work, but is how the posix_fallocate() > > and posix_fadvise() are specified by Posix. The patch is wrong, see also > > r261080 and r288640. > > Umm, I can't find the code ATM but syscalls store the actual return > value in td_retval and return 0 or EWHATEVER and the syscall wrapper > handles the translation. If that's not what Maxim was talking about, > then please ignore me. I mean that typical syscall does not return error to usermode, it returns -1 and sets errno. But usermode conventions for the posix_f*e() are different, and I believe this is what tripped over Maxim and I reacted upon. Indeed kernel expects the syscall function from the sysentvec table to return error or zero. If zero is returned, then td_retval array is translated into return value for usermode by cpu_set_syscall_retval(). If non-zero is returned, typical kernel/libc interface returns the syscall function return value to usermode and additionally set flag (like PSL_C in the processor status word). Of course, there is an additional translation layer in usermode syscall trampolines. > > Anyway, happy to hear that the X/Open group have found a new way to > screw people over. It is the same as the pthread_* conventions. They are somewhat consistent.