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Re: [PATCH v5 2/6] 9pfs: fix qemu_mknodat(S_IFSOCK) on macOS
From: |
Greg Kurz |
Subject: |
Re: [PATCH v5 2/6] 9pfs: fix qemu_mknodat(S_IFSOCK) on macOS |
Date: |
Fri, 29 Apr 2022 16:35:07 +0200 |
On Fri, 29 Apr 2022 15:50:35 +0200
Christian Schoenebeck <qemu_oss@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_oss@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_oss@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 <groug@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);
>
>
[PATCH v5 3/6] 9pfs: fix wrong encoding of rdev field in Rgetattr on macOS, Christian Schoenebeck, 2022/04/29
[PATCH v5 4/6] 9pfs: fix wrong errno being sent to Linux client on macOS host, Christian Schoenebeck, 2022/04/29
- Re: [PATCH v5 4/6] 9pfs: fix wrong errno being sent to Linux client on macOS host, Bin Meng, 2022/04/29
- Re: [PATCH v5 4/6] 9pfs: fix wrong errno being sent to Linux client on macOS host, Greg Kurz, 2022/04/29
- Re: [PATCH v5 4/6] 9pfs: fix wrong errno being sent to Linux client on macOS host, Christian Schoenebeck, 2022/04/29
- Re: [PATCH v5 4/6] 9pfs: fix wrong errno being sent to Linux client on macOS host, Greg Kurz, 2022/04/29
- Re: [PATCH v5 4/6] 9pfs: fix wrong errno being sent to Linux client on macOS host, Bin Meng, 2022/04/29
- Re: [PATCH v5 4/6] 9pfs: fix wrong errno being sent to Linux client on macOS host, Greg Kurz, 2022/04/29