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 53536C433F5 for ; Tue, 8 Feb 2022 18:07:14 +0000 (UTC) Received: from localhost ([::1]:37080 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nHUtU-00049G-Gl for qemu-devel@archiver.kernel.org; Tue, 08 Feb 2022 13:07:13 -0500 Received: from eggs.gnu.org ([209.51.188.92]:58692) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nHT67-0003aq-DT for qemu-devel@nongnu.org; Tue, 08 Feb 2022 11:12:09 -0500 Received: from kylie.crudebyte.com ([5.189.157.229]:58695) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nHT63-0000Cg-Ca for qemu-devel@nongnu.org; Tue, 08 Feb 2022 11:12:06 -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=R7O9h9rEck/xHcMRKKfJRag72csm50iikw2j7xpRPpk=; b=urgFgbjsKB66tr6aeRXPN/+klH yYRPqJpBkARiW0K/QAi/wiKWFxv+lRu0yauHq8DbxRPc9c0x8KRj5wSNxBQ8hgwQXYpRHTs+dROCp WonbeGy+LD9yFRb34tUFhPriMpXmsJwAw8yvsNpRyMGxoJMHbxlIIrIucU392oLBnAS/6pq+DL0Dw JHjze91ze+jaHrA6iAz7+Ne/BGKI2z4PX58/fmnLamtKbJ4A/dr+J6I7v36hx1FPcUBpv/xIMVBWF B84G4ibuLXMg6qQKzLDy8GgQTExfQkyHJYBWD6aUShmp6E1wTIF9htn0+uUuqdQuoQZfIy0IAUlfL uL+BxRSHQCWyn7O1XS3EIOIADT+5aoQEqtwVdzL6EwjYUw1vs1wb1sc+7AlSciaEPqadlqiuMS8Ta UYdhaf0buLz30BwAAcuV4glXIKUrEZQXP+tuU5RZBhEReiPFJ0tvklXRS9U42pPAP6l0PRdYO7L4I soyy8jfovOZ+VaAvKNeu7rPvuA0ybQomPVVq6Qm6FZrdvfEMyZxA/HvVDy42ZXGymmJxykjWY/WjQ eEQZx1lVhptsPUMamRW6Uz4EKdy+2guOKiQor9fovs9t465o2N+4UNGOziAOB1gsSfOYyEoryRv5L pdWx+5w+XNO22fUwqSsZ7VB4IXZ1JwyoOYjy+JLPM=; 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 Subject: Re: [PATCH v5 09/11] 9p: darwin: Implement compatibility for mknodat Date: Tue, 08 Feb 2022 17:11:56 +0100 Message-ID: <8390824.yUqPNeXlkU@silver> In-Reply-To: References: <20220207224024.87745-1-wwcohen@gmail.com> <44442748.7pOeeLDITA@silver> 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 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 > 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