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 54FF6C433F5 for ; Tue, 22 Feb 2022 14:31:44 +0000 (UTC) Received: from localhost ([::1]:36574 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nMWCd-0000UN-1i for qemu-devel@archiver.kernel.org; Tue, 22 Feb 2022 09:31:43 -0500 Received: from eggs.gnu.org ([209.51.188.92]:40668) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nMW8Q-0005vP-4F for qemu-devel@nongnu.org; Tue, 22 Feb 2022 09:27:22 -0500 Received: from kylie.crudebyte.com ([5.189.157.229]:35189) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nMW8L-0003I3-RD for qemu-devel@nongnu.org; Tue, 22 Feb 2022 09:27:21 -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=ZTfq0jIHasylWhYbaLGDmnqV7MWZmPPSEQnnwIxNMv4=; b=ChIv1xGZF15Psnc2hEqLAYTclZ GvxgbaFlUEfZdXqmIJZN2+X5vP1BJD6aw3FG6EKXgRpdXE0sdatfHa4hjTQ42bIyGjr4vfAi6YEwd JRFpl0PmApo+w1NJDKJeUHX43fTenCT2QkPYm6MAxzIOHXfKFGYnVNMynqVR40Po/5HG7wb1yn0pz ri2AgPvIAVzFd374JRrfHNCKGnWxo7OuM2ji8k3KTmjqfxEFzPniAyFbqz6c6jkmqoBfCDeC913LN swENT1odqGAkQ2ZB4mQLsSfXHUuU5fZ15uhOadb7lGbaETLEAPtuVIf4gJEAxpAxZA1+Em+pDe1jv teSDDHDVBarMl3Q5QXjl3FD9LjZj+qVXwEjvVkrr0gFL9HeUUd2VbFaGLB+QsgT6L/aghwAc6kvzq XRuKOjOi5EN/7Z/mWhA99Cgzr3KPp1h2Kv7AOm8ohESTu/W6d/VmNEs7uzO1kOk2Bho4VuQh1ssJ7 3dK7MZzV3LxqQgEyxKWyWqd55Co3UDiX1vFOkWoeqB0ljZ163P57KDnOo4zSGEz5BhK+BpGcP19r5 H5FU/IBzLUDeZkngG15SGUMl/SEehC5699AlOMZJTF07f4JWTKs/H1kT6Ykd/+aCRXHuEdvnyegtH bTZDHKiLe8MZlyHKI3mGtPX1sOYHPBZg+S8i578LU=; From: Christian Schoenebeck To: qemu-devel@nongnu.org Cc: Will Cohen , Laurent Vivier , Thomas Huth , Philippe =?ISO-8859-1?Q?Mathieu=2DDaud=E9?= , Greg Kurz , hi@alyssa.is, Michael Roitzsch , Paolo Bonzini , Keno Fischer Subject: Re: [PATCH v8 09/11] 9p: darwin: Implement compatibility for mknodat Date: Tue, 22 Feb 2022 15:27:13 +0100 Message-ID: <8571874.GWnKUVsiaS@silver> In-Reply-To: <20220220165056.72289-10-wwcohen@gmail.com> References: <20220220165056.72289-1-wwcohen@gmail.com> <20220220165056.72289-10-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 Sonntag, 20. Februar 2022 17:50:54 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 this 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 > - Move pthread_fchdir_np declaration only to osdep > - Declare pthread_fchdir_np with > - __attribute__((weak_import)) to allow checking for > its presence before usage > - Move declarations above cplusplus guard > - Add CONFIG_PTHREAD_FCHDIR_NP to meson and check for > presence in osdep.h and os-posix.c > - Rebase to apply cleanly on top of the 2022-02-10 > changes to 9pfs] > Signed-off-by: Will Cohen > --- > hw/9pfs/9p-local.c | 4 ++-- > include/qemu/osdep.h | 12 ++++++++++++ > meson.build | 1 + > os-posix.c | 35 +++++++++++++++++++++++++++++++++++ > 4 files changed, 50 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 ce12f64853..c0f442d791 100644 > --- a/include/qemu/osdep.h > +++ b/include/qemu/osdep.h > @@ -818,6 +818,18 @@ static inline int > platform_does_not_support_system(const char *command) */ > struct dirent *qemu_dirent_dup(struct dirent *dent); > > +/* > + * 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. pthread_fchdir_np is weakly linked here as a guard > + * in case it disappears in future macOS versions, because it is > + * is a private API. > + */ > +#if defined CONFIG_DARWIN && defined CONFIG_PTHREAD_FCHDIR_NP > +int pthread_fchdir_np(int fd) __attribute__((weak_import)); > +#endif > +int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev); > + > #ifdef __cplusplus > } > #endif Peter just informed me that osdep.h is not the right place to add something like this: https://lore.kernel.org/qemu-devel/CAFEAcA_=HAUNomKD2wurSVaAHa5mrk22A1oHKLWUDjk7v6Khmg@mail.gmail.com/ So this should be moved into a different header file. > diff --git a/meson.build b/meson.build > index ae5f7eec6e..6fdc0281ad 100644 > --- a/meson.build > +++ b/meson.build > @@ -1557,6 +1557,7 @@ config_host_data.set('CONFIG_POSIX_FALLOCATE', > cc.has_function('posix_fallocate' > config_host_data.set('CONFIG_POSIX_MEMALIGN', > cc.has_function('posix_memalign')) config_host_data.set('CONFIG_PPOLL', > cc.has_function('ppoll')) > config_host_data.set('CONFIG_PREADV', cc.has_function('preadv', prefix: > '#include ')) +config_host_data.set('CONFIG_PTHREAD_FCHDIR_NP', > cc.has_function('pthread_fchdir_np')) > config_host_data.set('CONFIG_SEM_TIMEDWAIT', > cc.has_function('sem_timedwait', dependencies: threads)) > config_host_data.set('CONFIG_SENDFILE', cc.has_function('sendfile')) > config_host_data.set('CONFIG_SETNS', cc.has_function('setns') and > cc.has_function('unshare')) diff --git a/os-posix.c b/os-posix.c > index ae6c9f2a5e..ccc3d1e9d3 100644 > --- a/os-posix.c > +++ b/os-posix.c > @@ -332,3 +332,38 @@ 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) > + */ > +#if defined CONFIG_DARWIN && defined CONFIG_PTHREAD_FCHDIR_NP > + > +int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev) > +{ > + int preserved_errno, err; > + if (!pthread_fchdir_np) { > + error_report_once("pthread_fchdir_np() is not available on this > version of macOS"); + return -ENOTSUP; > + } > + 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