On Fri, 29 Apr 2022 15:50:35 +0200 Christian Schoenebeck <qemu_...@crudebyte.com> wrote:
> On Freitag, 29. April 2022 14:56:50 CEST Greg Kurz wrote: > > On Fri, 29 Apr 2022 12:25:11 +0200 > > > > Christian Schoenebeck <qemu_...@crudebyte.com> wrote: > > > mknod() on macOS does not support creating sockets, so divert to > > > call sequence socket(), bind() and fchmodat() respectively if S_IFSOCK > > > was passed with mode argument. > > > > > > Link: https://lore.kernel.org/qemu-devel/17933734.zYzKuhC07K@silver/ > > > Signed-off-by: Christian Schoenebeck <qemu_...@crudebyte.com> > > > --- > > > > > > hw/9pfs/9p-util-darwin.c | 42 +++++++++++++++++++++++++++++++++++++++- > > > 1 file changed, 41 insertions(+), 1 deletion(-) > > > > > > diff --git a/hw/9pfs/9p-util-darwin.c b/hw/9pfs/9p-util-darwin.c > > > index e24d09763a..619c403ba7 100644 > > > --- a/hw/9pfs/9p-util-darwin.c > > > +++ b/hw/9pfs/9p-util-darwin.c > > > @@ -74,6 +74,42 @@ int fsetxattrat_nofollow(int dirfd, const char > > > *filename, const char *name,> > > > */ > > > > > > #if defined CONFIG_PTHREAD_FCHDIR_NP > > > > > > +static int create_socket_file_at_cwd(const char *filename, mode_t mode) { > > > + int fd, err; > > > + struct sockaddr_un addr = { > > > + .sun_family = AF_UNIX > > > + }; > > > + > > > + err = snprintf(addr.sun_path, sizeof(addr.sun_path), "./%s", > > > filename); + if (err < 0 || err >= sizeof(addr.sun_path)) { > > > > According to POSIX [1]: > > > > The snprintf() function shall fail if: > > > > [EOVERFLOW] > > [CX] [Option Start] The value of n is greater than {INT_MAX}. [Option End] > > > > [1] https://pubs.opengroup.org/onlinepubs/9699919799/functions/snprintf.html > > > > Since we're passing sizeof(addr.sun_path), I'm pretty sure snprintf() > > cannot fail. No big deal. > > The question is whom you would want to trust on this? POSIX? ISO-C? Clang? > BSD? Apple? And for how long into future? I mean in general yes, I would not To improve overall portability across all possible hosts, I'd stick to POSIX semantics but here this is macOS only code so you can assume this is Apple's snprintf(). > expect it to fail with -1 here either, but there are various different API > docs on snprintf() out there, and most of them don't even bother to enumarate > which encoding errors may happen. And I'm pretty sure if I'd drop the > negative > err check here, then Akihiko would slap me for unforeseeable additional error > cases on snprintf() that may be added in future. > /o\ ;-) > Apple's documentation on snprintf() BTW just says: > > "These functions return a negative value if an error occurs." > How valuable this is !!! ;-) > So Apple does not even restrict the return value to -1 on errrors, you would > also need to expect other negative values. > > So on doubt, I leave this negative result check for now. ;-) > Fair enough. > > Reviewed-by: Greg Kurz <gr...@kaod.org> > > Thanks! > > Best regards > Christian Schoenebeck > > > > + errno = ENAMETOOLONG; > > > + return -1; > > > + } > > > + fd = socket(PF_UNIX, SOCK_DGRAM, 0); > > > + if (fd == -1) { > > > + return fd; > > > + } > > > + err = bind(fd, (struct sockaddr *) &addr, sizeof(addr)); > > > + if (err == -1) { > > > + goto out; > > > + } > > > + /* > > > + * FIXME: Should rather be using descriptor-based fchmod() on the > > > + * socket file descriptor above (preferably before bind() call), > > > + * instead of path-based fchmodat(), to prevent concurrent transient > > > + * state issues between creating the named FIFO file at bind() and > > > + * delayed adjustment of permissions at fchmodat(). However currently > > > + * macOS (12.x) does not support such operations on socket file > > > + * descriptors yet. > > > + * > > > + * Filed report with Apple: FB9997731 > > > + */ > > > + err = fchmodat(AT_FDCWD, filename, mode, AT_SYMLINK_NOFOLLOW_ANY); > > > +out: > > > + close_preserve_errno(fd); > > > + return err; > > > +} > > > + > > > > > > int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev) > > > { > > > > > > int preserved_errno, err; > > > > > > @@ -93,7 +129,11 @@ int qemu_mknodat(int dirfd, const char *filename, > > > mode_t mode, dev_t dev)> > > > if (pthread_fchdir_np(dirfd) < 0) { > > > > > > return -1; > > > > > > } > > > > > > - err = mknod(filename, mode, dev); > > > + if (S_ISSOCK(mode)) { > > > + err = create_socket_file_at_cwd(filename, mode); > > > + } else { > > > + err = mknod(filename, mode, dev); > > > + } > > > > > > preserved_errno = errno; > > > /* Stop using the thread-local cwd */ > > > pthread_fchdir_np(-1); > >
