| Message ID | 20220210132946.2303-10-wwcohen@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | 9p: Add support for darwin | expand |
On 10/2/22 14:29, Will Cohen wrote: > From: Keno Fischer <keno@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 <keno@juliacomputing.com> > Signed-off-by: Michael Roitzsch <reactorcontrol@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] > Signed-off-by: Will Cohen <wwcohen@gmail.com> > --- > hw/9pfs/9p-local.c | 4 ++-- > include/qemu/osdep.h | 12 ++++++++++++ > os-posix.c | 35 +++++++++++++++++++++++++++++++++++ > 3 files changed, 49 insertions(+), 2 deletions(-) > +/* > + * 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. > + */ > +#ifdef CONFIG_DARWIN > +int pthread_fchdir_np(int fd) __attribute__((weak_import)); > +#endif Please use Meson to define CONFIG_PTHREAD_FCHDIR_NP, similar to commits 10f6b23187 ("configure, meson: move pthread_setname_np checks to Meson") and 479a57475e ("util: Implement debug-threads for macOS").
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..d8cc7240ed 100644 --- a/include/qemu/osdep.h +++ b/include/qemu/osdep.h @@ -805,6 +805,18 @@ static inline int platform_does_not_support_system(const char *command) } #endif /* !HAVE_SYSTEM_FUNCTION */ +/* + * 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. + */ +#ifdef CONFIG_DARWIN +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 diff --git a/os-posix.c b/os-posix.c index ae6c9f2a5e..28a294b8b3 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) + */ +#ifdef CONFIG_DARWIN + +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