On Mon, Feb 7, 2022 at 5:48 PM Christian Schoenebeck <qemu_...@crudebyte.com>
wrote:
> On Montag, 7. Februar 2022 22:07:34 CET Will Cohen wrote:
> > On Mon, Feb 7, 2022 at 9:21 AM Christian Schoenebeck
> > <qemu_...@crudebyte.com>
> > wrote:
> > > On Montag, 7. Februar 2022 11:57:25 CET Dr. David Alan Gilbert wrote:
> > > > * Greg Kurz (gr...@kaod.org) wrote:
> > > > > On Mon, 7 Feb 2022 11:30:18 +0100
> > > > >
> > > > > Philippe Mathieu-Daudé <f4...@amsat.org> wrote:
> > > > > > On 7/2/22 09:47, Greg Kurz wrote:
> > > > > > > On Sun, 6 Feb 2022 20:10:23 -0500
> > > > > > >
> > > > > > > Will Cohen <wwco...@gmail.com> wrote:
> > > > > > >> This patch set currently places it in 9p-util only because 9p
> is
> > >
> > > the
> > >
> > > > > > >> only
> > > > > > >> place where this issue seems to have come up so far and we
> were
> > >
> > > wary
> > >
> > > > > > >> of
> > > > > > >> editing files too far afield, but I have no attachment to its
> > > > > > >> specific
> > > > > > >> location!
> > > > > > >
> > > > > > > Inline comments are preferred on qemu-devel. Please don't top
> post
> > >
> > > !
> > >
> > > > > > > This complicates the review a lot.
> > > > > > >
> > > > > > > This is indeed a good candidate for osdep. This being said,
> unless
> > > > > > > there's
> > > > > > > some other user in the QEMU code base, it is acceptable to
> leave
> > > > > > > it
> > > > > > > under
> > > > > > > 9pfs.
> > > > > >
> > > > > > virtiofsd could eventually use it.
> > > > >
> > > > > Indeed but virtiofsd is for linux hosts only AFAICT and I'm not
> aware
> > >
> > > of
> > >
> > > > > any work to support any other host OS.
> > > > >
> > > > > Cc'ing virtio-fs people for inputs on this topic.
> > > >
> > > > Indeeed, there's a lot of Linux specific code in the virtiofsd - I
> know
> > > > people are interested in other platforms, but I'm not sure that's the
> > > > right starting point.
> > > >
> > > > Dave
> > >
> > > Agreeing with Greg here: i.e. I would have placed this into osdep, but
> I
> > > would
> > > not insist on it either.
> > >
> > > Best regards,
> > > Christian Schoenebeck
> >
> > This makes sense. A revised version of this patch, moving qemu_mknodat
> from
> > 9p-util to osdep and os-posix, is attached below. I'd appreciate any
> > feedback from those looped in here, so that the context isn't lost before
> > resubmitting as a v5 patch, especially since this is starting to touch
> > files outside of 9p.
> >
> > From c9713c87163da7c96b5357d0d85ac318ae3d3051 Mon Sep 17 00:00:00 2001
> > From: Keno Fischer <k...@juliacomputing.com>
> > Date: Sat, 16 Jun 2018 20:56:55 -0400
> > Subject: [PATCH] 9p: darwin: Implement compatibility for mknodat
> >
> > 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>
> > ---
> > 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.
>
> > +
> > +int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t
> dev)
> > +{
> > + int preserved_errno, err;
> > + 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
>
Noted and all of that makes sense to me. Sorry about trying to lump this in
v4. If more things come up with v5 I'll stick these changes in for v6 as
well. If there's no other major comments with v5, I can either still
resubmit as v6 or defer to whatever process is easiest for the maintainers
to integrate, given that I accept all of these modifications.
