From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 83EADC433F5 for ; Tue, 8 Feb 2022 20:03:21 +0000 (UTC) Received: from localhost ([::1]:46514 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nHWhr-0003G2-Pa for qemu-devel@archiver.kernel.org; Tue, 08 Feb 2022 15:03:19 -0500 Received: from eggs.gnu.org ([209.51.188.92]:44544) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nHVEB-0003Rq-GO for qemu-devel@nongnu.org; Tue, 08 Feb 2022 13:28:35 -0500 Received: from kylie.crudebyte.com ([5.189.157.229]:60593) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nHVE7-0006u2-G4 for qemu-devel@nongnu.org; Tue, 08 Feb 2022 13:28:35 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=crudebyte.com; s=kylie; h=Content-Type:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Content-ID:Content-Description; bh=lha7D0rSpQwEETYaLscp7WIUcFcaG9ww9d3rHyEc3l8=; b=uw2SsEAMrxGZZACpxe5U6YGfjm l0nuY+wg61BEVkddcTpoYWCFQsFniSDSq3XcHnTWNlPE/3Fd2CvZs+1mPDZUYcv2xlXtAlcmD1BnP 0XYvbxOLsauYyrLcDU4v41P9+YKAUtd+2EGTi8danlQy0w0Y5kTUSquyZ9U5hEr1ZupvnyEuJt33R 2w60ss00aYJUoxGjqn21T6TVW6R2lbL+8T2WPGykxfiW5vnXcmaTwgPkjESr0QXK2hp0jDhKj3oFF Xt2mDP7Ao6vEdJQI2eBeNfS3Nwuz0Eb58niD0FUFjfwnQ8BxtttdptI1x2mF/GyBXZ9vEiDBl2qKg 8V3dhxOKWNxMvtRNA2yAERy1vHYoaTXdg0JDlrqpl3gVy6082FN7GW6WTWGSX47E89P1fMpc8BIqd XG7n6lmJgRy0CwYnIWp86zhbZimurSQ+XpnIm9YRQTufcbhPxQvjwRiD5RawjwQMlqlq211Lx1O31 3nCR9JQa9BSFCE3cTM5BqP+cNorxCwlDFr4ULlZ9uvaV17+yE8rysKICvjmPsQmrPSIZ+25udr3vf X9u7tQvpDKo0svLHJdzvdWpIqJ9EeKBxG2iERJ6Xb0IOH8T5KSjVmhMCqet97j2VnFzv1ynuysykq Wm3ee6ZW64BbRqRd0tiQSyZXW3FqgQ2XF3y8YxgYU=; From: Christian Schoenebeck To: Will Cohen Cc: qemu-devel@nongnu.org, hi@alyssa.is, Greg Kurz , Paolo Bonzini , Thomas Huth , Laurent Vivier , Keno Fischer , Michael Roitzsch , Akihiko Odaki Subject: Re: [PATCH v5 09/11] 9p: darwin: Implement compatibility for mknodat Date: Tue, 08 Feb 2022 19:28:21 +0100 Message-ID: <4809377.qIIDLkA7W8@silver> In-Reply-To: References: <20220207224024.87745-1-wwcohen@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Received-SPF: pass client-ip=5.189.157.229; envelope-from=qemu_oss@crudebyte.com; helo=kylie.crudebyte.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Dienstag, 8. Februar 2022 19:04:31 CET Will Cohen wrote: > On Tue, Feb 8, 2022 at 11:19 AM Will Cohen wrote: > > On Tue, Feb 8, 2022 at 11:11 AM Christian Schoenebeck < > > > > qemu_oss@crudebyte.com> wrote: > >> On Dienstag, 8. Februar 2022 16:57:55 CET Will Cohen wrote: > >> > My inclination is to go with the __builtin_available(macOS 10.12, *) > >> > >> path, > >> > >> > if acceptable, since it partially mirrors the API_AVAILABLE macro idea. > >> > >> I > >> > >> OTOH that's duplication of the ">= macOS 10.12" info, plus > >> __builtin_available > >> is direct use of a clang-only extension, whereas API_AVAILABLE() works > >> (or > >> more precisely: doesn't error out at least) with other compilers like GCC > >> as > >> well. GCC is sometimes used for cross-compilation. > >> > >> Moreover, I would also add an error message in this case, e.g.: > >> if (!pthread_fchdir_np) { > >> > >> error_report_once("pthread_fchdir_np() is not available on this > >> > >> macOS version"); > >> > >> return -ENOTSUPP; > >> > >> } > >> > >> I should elaborate why I think this is needed: you are already doing a > >> Meson > >> check for the existence of pthread_fchdir_np(), but the system where QEMU > >> is > >> compiled and the systems where the compiled binary will be running, might > >> be > >> different ones (i.e. different macOS versions). > >> > >> Best regards, > >> Christian Schoenebeck > > > > Agreed, that way actually closes the edge case. Something along these > > lines briefly crossed my mind during a previous version, but I quickly got > > passed it by assuming that the compiling entity would always be the > > bottleneck, which makes no sense in hindsight, so I very much appreciate > > that you caught this. > > Ah, rebuilding leads to a compiler error: > > ../os-posix.c:348:10: warning: address of function 'pthread_fchdir_np' will > always evaluate to 'true' [-Wpointer-bool-conversion] > if (!pthread_fchdir_np) { > ~^~~~~~~~~~~~~~~~~ > > I don't have a machine that's pre-10.12 so I can't see what the result is > there, but this might be why the __builtin_available approach got taken. I guess that's because you are compiling QEMU with minimum deployment target being macOS >= 10.12 already. In this case the compiler won't make pthread_fchdir_np a weak link, it only does emit a weak link if you are targeting macOS versions prior than the defined availablity attribute, hence the address would never be NULL here and hence the compiler warning. So I guess it is okay if you just omit checking presence of pthread_fchdir_np at runtime and just assume it exists. Added Akihiko on CC, just in case he would have something to add on this macOS issue here. :) Best regards, Christian Schoenebeck > >> > guess it's perhaps a tradeoff between predicting the future unknown > >> > availability of functions versus just ensuring a minimum macOS version > >> > >> and > >> > >> > hoping for the best. With any luck, the distinction between the two > >> > approaches will be moot, if we try to assume that a future macOS > >> > version > >> > that removes this also provides mknodat. > >> > > >> > On Tue, Feb 8, 2022 at 10:03 AM Christian Schoenebeck < > >> > > >> > qemu_oss@crudebyte.com> wrote: > >> > > On Dienstag, 8. Februar 2022 14:36:42 CET Will Cohen wrote: > >> > > > On Mon, Feb 7, 2022 at 5:56 PM Christian Schoenebeck > >> > > > > >> > > > > >> > > > wrote: > >> > > > > On Montag, 7. Februar 2022 23:40:22 CET Will Cohen wrote: > >> > > > > > From: Keno Fischer > >> > > > > > > >> > > > > > Darwin does not support mknodat. However, to avoid race > >> > >> conditions > >> > >> > > > > > with later setting the permissions, we must avoid using mknod > >> > > > > > on > >> > > > > > the full path instead. We could try to fchdir, but that would > >> > >> cause > >> > >> > > > > > problems if multiple threads try to call mknodat at the same > >> > >> time. > >> > >> > > > > > However, luckily there is a solution: Darwin includes a > >> > > > > > function > >> > > > > > that sets the cwd for the current thread only. > >> > > > > > This should suffice to use mknod safely. > >> > > > > > > >> > > > > > This function (pthread_fchdir_np) is protected by a check in > >> > > > > > meson in a patch later in tihs series. > >> > > > > > > >> > > > > > Signed-off-by: Keno Fischer > >> > > > > > Signed-off-by: Michael Roitzsch > >> > > > > > [Will Cohen: - Adjust coding style > >> > > > > > > >> > > > > > - Replace clang references with gcc > >> > > > > > - Note radar filed with Apple for missing syscall > >> > > > > > - Replace direct syscall with pthread_fchdir_np > >> > > > > > and > >> > > > > > > >> > > > > > adjust patch notes accordingly > >> > > > > > > >> > > > > > - Move qemu_mknodat from 9p-util to osdep and > >> > >> os-posix] > >> > >> > > > > > Signed-off-by: Will Cohen > >> > > > > > --- > >> > > > > > >> > > > > Like already mentioned by me moments ago on previous v4 (just > >> > >> echoing) > >> > >> > > ... > >> > > > >> > > > > > hw/9pfs/9p-local.c | 4 ++-- > >> > > > > > include/qemu/osdep.h | 10 ++++++++++ > >> > > > > > os-posix.c | 34 ++++++++++++++++++++++++++++++++++ > >> > > > > > 3 files changed, 46 insertions(+), 2 deletions(-) > >> > > > > > > >> > > > > > diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c > >> > > > > > index a0d08e5216..d42ce6d8b8 100644 > >> > > > > > --- a/hw/9pfs/9p-local.c > >> > > > > > +++ b/hw/9pfs/9p-local.c > >> > > > > > @@ -682,7 +682,7 @@ static int local_mknod(FsContext *fs_ctx, > >> > > > >> > > V9fsPath > >> > > > >> > > > > > *dir_path, > >> > > > > > > >> > > > > > if (fs_ctx->export_flags & V9FS_SM_MAPPED || > >> > > > > > > >> > > > > > fs_ctx->export_flags & V9FS_SM_MAPPED_FILE) { > >> > > > > > > >> > > > > > - err = mknodat(dirfd, name, fs_ctx->fmode | S_IFREG, > >> > > > > > 0); > >> > > > > > + err = qemu_mknodat(dirfd, name, fs_ctx->fmode | > >> > >> S_IFREG, > >> > >> > > > > > 0); > >> > > > > > > >> > > > > > if (err == -1) { > >> > > > > > > >> > > > > > goto out; > >> > > > > > > >> > > > > > } > >> > > > > > > >> > > > > > @@ -697,7 +697,7 @@ static int local_mknod(FsContext *fs_ctx, > >> > > > >> > > V9fsPath > >> > > > >> > > > > > *dir_path, } > >> > > > > > > >> > > > > > } else if (fs_ctx->export_flags & V9FS_SM_PASSTHROUGH || > >> > > > > > > >> > > > > > fs_ctx->export_flags & V9FS_SM_NONE) { > >> > > > > > > >> > > > > > - err = mknodat(dirfd, name, credp->fc_mode, > >> > >> credp->fc_rdev); > >> > >> > > > > > + err = qemu_mknodat(dirfd, name, credp->fc_mode, > >> > > > > > credp->fc_rdev); > >> > > > > > > >> > > > > > if (err == -1) { > >> > > > > > > >> > > > > > goto out; > >> > > > > > > >> > > > > > } > >> > > > > > > >> > > > > > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h > >> > > > > > index d1660d67fa..f3a8367ece 100644 > >> > > > > > --- a/include/qemu/osdep.h > >> > > > > > +++ b/include/qemu/osdep.h > >> > > > > > @@ -810,3 +810,13 @@ static inline int > >> > > > > > platform_does_not_support_system(const char *command) #endif > >> > > > > > > >> > > > > > #endif > >> > > > > > > >> > > > > > + > >> > > > > > +/* > >> > > > > > + * As long as mknodat is not available on macOS, this > >> > >> workaround > >> > >> > > > > > + * using pthread_fchdir_np is needed. qemu_mknodat is defined > >> > >> in > >> > >> > > > > > + * os-posix.c > >> > > > > > + */ > >> > > > > > +#ifdef CONFIG_DARWIN > >> > > > > > +int pthread_fchdir_np(int fd); > >> > > > > > +#endif > >> > > > > > >> > > > > I would make that: > >> > > > > > >> > > > > #ifdef CONFIG_DARWIN > >> > > > > int pthread_fchdir_np(int fd) API_AVAILABLE(macosx(10.12)); > >> > > > > #endif > >> > > > > > >> > > > > here and ... > >> > > > > > >> > > > > > +int qemu_mknodat(int dirfd, const char *filename, mode_t mode, > >> > > > > > dev_t > >> > > > > > >> > > > > dev); > >> > > > > > >> > > > > > diff --git a/os-posix.c b/os-posix.c > >> > > > > > index ae6c9f2a5e..95c1607065 100644 > >> > > > > > --- a/os-posix.c > >> > > > > > +++ b/os-posix.c > >> > > > > > @@ -24,6 +24,7 @@ > >> > > > > > > >> > > > > > */ > >> > > > > > > >> > > > > > #include "qemu/osdep.h" > >> > > > > > > >> > > > > > +#include > >> > > > > > > >> > > > > > #include > >> > > > > > #include > >> > > > > > #include > >> > > > > > > >> > > > > > @@ -332,3 +333,36 @@ int os_mlock(void) > >> > > > > > > >> > > > > > return -ENOSYS; > >> > > > > > > >> > > > > > #endif > >> > > > > > } > >> > > > > > > >> > > > > > + > >> > > > > > +/* > >> > > > > > + * As long as mknodat is not available on macOS, this > >> > >> workaround > >> > >> > > > > > + * using pthread_fchdir_np is needed. > >> > > > > > + * > >> > > > > > + * Radar filed with Apple for implementing mknodat: > >> > > > > > + * rdar://FB9862426 (https://openradar.appspot.com/FB9862426) > >> > > > > > + */ > >> > > > > > +#ifdef CONFIG_DARWIN > >> > > > > > + > >> > > > > > +int pthread_fchdir_np(int fd) API_AVAILABLE(macosx(10.12)); > >> > > > > > >> > > > > ... drop the duplicate declaration of pthread_fchdir_np() here. > >> > > > > >> > > > Trying this out, it reminds me that this use of API_AVAILABLE in > >> > > > >> > > os-posix.c > >> > > > >> > > > relies on the added #include . > >> > > > > >> > > > Leaving the include out leads to: > >> > > > .../include/qemu/osdep.h:820:31: error: expected function body > >> > > > after > >> > > > function declarator > >> > > > int pthread_fchdir_np(int fd) API_AVAILABLE(macosx(10.12)); > >> > > > > >> > > > ^ > >> > > > > >> > > > 1 error generated. > >> > > > ninja: build stopped: subcommand failed. > >> > > > make[1]: *** [run-ninja] Error 1 > >> > > > make: *** [all] Error 2 > >> > > > > >> > > > The admonition against modifying osdep.h's includes too much led me > >> > >> to > >> > >> > > > steer away from putting it all in there. If there's no issue with > >> > >> adding > >> > >> > > > +#include to osdep.h, then this change makes > >> > >> sense > >> > >> > > > to > >> > > > me. > >> > > > >> > > If you embed that include into ifdefs, sure! > >> > > > >> > > #ifdef CONFIG_DARWIN > >> > > /* defines API_AVAILABLE(...) */ > >> > > #include > >> > > #endif > >> > > > >> > > One more thing though ... > >> > > > >> > > > > > + > >> > > > > > +int qemu_mknodat(int dirfd, const char *filename, mode_t mode, > >> > > > > > dev_t > >> > > > > > >> > > > > dev) > >> > > > > > >> > > > > > +{ > >> > > > > > + int preserved_errno, err; > >> > > > >> > > pthread_fchdir_np() is weakly linked. So I guess here should be a > >> > >> check > >> > >> > > like: > >> > > if (!pthread_fchdir_np) { > >> > > > >> > > return -ENOTSUPP; > >> > > > >> > > } > >> > > > >> > > Before trying to call pthread_fchdir_np() below. As already discussed > >> > >> with > >> > >> > > the > >> > > Chromium [1] example, some do that a bit differently by using > >> > > > >> > > __builtin_available(): > >> > > if (__builtin_available(macOS 10.12, *)) { > >> > > > >> > > return -ENOTSUPP; > >> > > > >> > > } > >> > > > >> > > Which makes me wonder why they are not doing a simple NULL check? > >> > > > >> > > [1] > >> > >> https://chromium.googlesource.com/chromium/src/+/lkgr/base/process/launch > >> _ > >> > >> > > mac.cc#110> > >> > > > >> > > > > > + if (pthread_fchdir_np(dirfd) < 0) { > >> > > > > > + return -1; > >> > > > > > + } > >> > > > > > + err = mknod(filename, mode, dev); > >> > > > > > + preserved_errno = errno; > >> > > > > > + /* Stop using the thread-local cwd */ > >> > > > > > + pthread_fchdir_np(-1); > >> > > > > > + if (err < 0) { > >> > > > > > + errno = preserved_errno; > >> > > > > > + } > >> > > > > > + return err; > >> > > > > > +} > >> > > > > > +#else > >> > > > > > +int qemu_mknodat(int dirfd, const char *filename, mode_t mode, > >> > > > > > dev_t > >> > > > > > >> > > > > dev) > >> > > > > > >> > > > > > +{ > >> > > > > > + return mknodat(dirfd, filename, mode, dev); > >> > > > > > +} > >> > > > > > +#endif Best regards, Christian Schoenebeck