On Fri, Feb 25, 2022 at 11:31 AM Christian Schoenebeck <
qemu_...@crudebyte.com> wrote:
> On Freitag, 25. Februar 2022 15:00:40 CET Will Cohen wrote:
> > On Tue, Feb 22, 2022 at 9:27 AM Christian Schoenebeck <
> >
> > qemu_...@crudebyte.com> wrote:
> > > On Sonntag, 20. Februar 2022 17:50:54 CET Will Cohen wrote:
> > > > From: Keno Fischer <k...@juliacomputing.com>
> > > >
> > > > 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 <k...@juliacomputing.com>
> > > > Signed-off-by: Michael Roitzsch <reactorcont...@icloud.com>
> > > > [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 <wwco...@gmail.com>
> > > > ---
> > > >
> > > > 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_=HAUNomKD2wurSVaAHa5mrk22A1oHKL
> > > wudjk7v6k...@mail.gmail.com/
> > >
> > > So this should be moved into a different header file.
> >
> > Does that logic apply here too? In some ways I'd say that mknodat falls
> > into the category of "things without which code would work on most
> > platforms but fail to compile or misbehave on a minority of host OSes."
> If
> > osdep.h is the wrong place, should it go back to 9p-util, where it lived
> > before it moved to osdep?
>
> The other function Peter wanted out from osdep.h would fall into that
> category
> as well. I understand it like "only put things into osdep.h as very last
> resort". CCing Peter on this. If he doesn't give you green light, or on
> doubt,
> then yes please move it from osdep -> 9p-util.
>
> Will, are you planning to send a v9 of this series soon? Next week I need
> to
> add changes that would collide with these here. So if you intend to send
> it
> soon, then I just wait so that we can finally queue these macOS patches
> here
> for QEMU 7.0, before I would go along with my changes.
>
> Best regards,
> Christian Schoenebeck
>
Prepping a v9 now based on all the other changes + the formatting issues.
I'll send this weekend if that's okay!
>
> > > > 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 <sys/uio.h>'))
> > >
> > > +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
>
>
>
