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
+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));
+
+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
--
2.34.1
