On Dienstag, 8. Februar 2022 19:28:21 CET Christian Schoenebeck wrote: > On Dienstag, 8. Februar 2022 19:04:31 CET Will Cohen wrote: > > On Tue, Feb 8, 2022 at 11:19 AM Will Cohen <wwco...@gmail.com> wrote: > > > On Tue, Feb 8, 2022 at 11:11 AM Christian Schoenebeck < > > > > > > qemu_...@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. :)
On a second thought: this case a bit special. Are we worried that pthread_fchdir_np() is "not yet" available on macOS, or "no longer" available. Probably both, right? So maybe it would make sense to replace the API_AVAILABLE() attribute directly with a __attribute__((weak)) attribute. Then the runtime check with the proposed error message would also trigger if a bleeding edge macOS version no longer has pthread_fchdir_np(). Also keep in mind: there are always also the MAC_OS_X_VERSION_MIN_REQUIRED and MAC_OS_X_VERSION_MAX_ALLOWED macros to query the deployment target at compile time to wrap deployment target dependent code accordingly. On doubt you could just make some tests there by simply "inventing" a non- existent function. 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_...@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 > > >> > > > <qemu_...@crudebyte.com> > > >> > > > > > >> > > > wrote: > > >> > > > > On Montag, 7. Februar 2022 23:40:22 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 tihs 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] > > >> > > >> > > > > > Signed-off-by: Will Cohen <wwco...@gmail.com> > > >> > > > > > --- > > >> > > > > > > >> > > > > 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 <os/availability.h> > > >> > > > > > > > >> > > > > > #include <sys/wait.h> > > >> > > > > > #include <pwd.h> > > >> > > > > > #include <grp.h> > > >> > > > > > > > >> > > > > > @@ -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 <os/availability.h>. > > >> > > > > > >> > > > 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 <os/availability.h> 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 <os/availability.h> > > >> > > #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/laun > > >> ch > > >> _ > > >> > > >> > > 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 Best regards, Christian Schoenebeck