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[PULL 09/19] 9p: darwin: Implement compatibility for mknodat
From: |
Christian Schoenebeck |
Subject: |
[PULL 09/19] 9p: darwin: Implement compatibility for mknodat |
Date: |
Fri, 04 Mar 2022 13:27:49 +0100 |
From: Keno Fischer <keno@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 this series.
Signed-off-by: Keno Fischer <keno@juliacomputing.com>
Signed-off-by: Michael Roitzsch <reactorcontrol@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
- Declare pthread_fchdir_np with
- __attribute__((weak_import)) to allow checking for
its presence before usage
- Move declarations above cplusplus guard
- Add CONFIG_PTHREAD_FCHDIR_NP to meson and check for
presence in 9p-util
- Rebase to apply cleanly on top of the 2022-02-10
changes to 9pfs
- Fix line over 90 characters formatting error]
Signed-off-by: Will Cohen <wwcohen@gmail.com>
Message-Id: <20220227223522.91937-10-wwcohen@gmail.com>
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Reviewed-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
---
hw/9pfs/9p-local.c | 4 ++--
hw/9pfs/9p-util-darwin.c | 33 +++++++++++++++++++++++++++++++++
hw/9pfs/9p-util-linux.c | 6 ++++++
hw/9pfs/9p-util.h | 11 +++++++++++
meson.build | 1 +
5 files changed, 53 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/hw/9pfs/9p-util-darwin.c b/hw/9pfs/9p-util-darwin.c
index cdb4c9e24c..bec0253474 100644
--- a/hw/9pfs/9p-util-darwin.c
+++ b/hw/9pfs/9p-util-darwin.c
@@ -7,6 +7,8 @@
#include "qemu/osdep.h"
#include "qemu/xattr.h"
+#include "qapi/error.h"
+#include "qemu/error-report.h"
#include "9p-util.h"
ssize_t fgetxattrat_nofollow(int dirfd, const char *filename, const char *name,
@@ -62,3 +64,34 @@ int fsetxattrat_nofollow(int dirfd, const char *filename,
const char *name,
close_preserve_errno(fd);
return ret;
}
+
+/*
+ * 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)
+ */
+#if defined CONFIG_PTHREAD_FCHDIR_NP
+
+int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev)
+{
+ int preserved_errno, err;
+ if (!pthread_fchdir_np) {
+ error_report_once("pthread_fchdir_np() not available on this version
of macOS");
+ return -ENOTSUP;
+ }
+ 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;
+}
+
+#endif
diff --git a/hw/9pfs/9p-util-linux.c b/hw/9pfs/9p-util-linux.c
index 398614a5d0..db451b0784 100644
--- a/hw/9pfs/9p-util-linux.c
+++ b/hw/9pfs/9p-util-linux.c
@@ -61,4 +61,10 @@ int fsetxattrat_nofollow(int dirfd, const char *filename,
const char *name,
ret = lsetxattr(proc_path, name, value, size, flags);
g_free(proc_path);
return ret;
+
+}
+
+int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev)
+{
+ return mknodat(dirfd, filename, mode, dev);
}
diff --git a/hw/9pfs/9p-util.h b/hw/9pfs/9p-util.h
index 9abff79884..1f74d37558 100644
--- a/hw/9pfs/9p-util.h
+++ b/hw/9pfs/9p-util.h
@@ -112,5 +112,16 @@ static inline off_t qemu_dirent_off(struct dirent *dent)
#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. pthread_fchdir_np is weakly linked here as a guard
+ * in case it disappears in future macOS versions, because it is
+ * is a private API.
+ */
+#if defined CONFIG_DARWIN && defined CONFIG_PTHREAD_FCHDIR_NP
+int pthread_fchdir_np(int fd) __attribute__((weak_import));
+#endif
+int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev);
#endif
diff --git a/meson.build b/meson.build
index a5b63e62cd..6058ea3896 100644
--- a/meson.build
+++ b/meson.build
@@ -1622,6 +1622,7 @@ config_host_data.set('CONFIG_POSIX_FALLOCATE',
cc.has_function('posix_fallocate'
config_host_data.set('CONFIG_POSIX_MEMALIGN',
cc.has_function('posix_memalign'))
config_host_data.set('CONFIG_PPOLL', cc.has_function('ppoll'))
config_host_data.set('CONFIG_PREADV', cc.has_function('preadv', prefix:
'#include <sys/uio.h>'))
+config_host_data.set('CONFIG_PTHREAD_FCHDIR_NP',
cc.has_function('pthread_fchdir_np'))
config_host_data.set('CONFIG_SEM_TIMEDWAIT', cc.has_function('sem_timedwait',
dependencies: threads))
config_host_data.set('CONFIG_SENDFILE', cc.has_function('sendfile'))
config_host_data.set('CONFIG_SETNS', cc.has_function('setns') and
cc.has_function('unshare'))
--
2.20.1
- [PULL 07/19] 9p: darwin: *xattr_nofollow implementations, (continued)
- [PULL 07/19] 9p: darwin: *xattr_nofollow implementations, Christian Schoenebeck, 2022/03/04
- [PULL 15/19] 9pfs/codir.c: convert Doxygen -> kerneldoc format, Christian Schoenebeck, 2022/03/04
- [PULL 19/19] fsdev/p9array.h: convert Doxygen -> kerneldoc format, Christian Schoenebeck, 2022/03/04
- [PULL 01/19] 9p: linux: Fix a couple Linux assumptions, Christian Schoenebeck, 2022/03/04
- [PULL 17/19] 9pfs/9p-util.h: convert Doxygen -> kerneldoc format, Christian Schoenebeck, 2022/03/04
- [PULL 16/19] 9pfs/9p.c: convert Doxygen -> kerneldoc format, Christian Schoenebeck, 2022/03/04
- [PULL 11/19] 9p: darwin: meson: Allow VirtFS on Darwin, Christian Schoenebeck, 2022/03/04
- [PULL 04/19] 9p: darwin: Handle struct dirent differences, Christian Schoenebeck, 2022/03/04
- [PULL 08/19] 9p: darwin: Compatibility for f/l*xattr, Christian Schoenebeck, 2022/03/04
- [PULL 02/19] 9p: Rename 9p-util -> 9p-util-linux, Christian Schoenebeck, 2022/03/04
- [PULL 09/19] 9p: darwin: Implement compatibility for mknodat,
Christian Schoenebeck <=
- [PULL 18/19] 9pfs/coth.h: drop Doxygen format on v9fs_co_run_in_worker(), Christian Schoenebeck, 2022/03/04
- [PULL 05/19] 9p: darwin: Ignore O_{NOATIME, DIRECT}, Christian Schoenebeck, 2022/03/04
- [PULL 10/19] 9p: darwin: Adjust assumption on virtio-9p-test, Christian Schoenebeck, 2022/03/04
- [PULL 06/19] 9p: darwin: Move XATTR_SIZE_MAX->P9_XATTR_SIZE_MAX, Christian Schoenebeck, 2022/03/04
- [PULL 14/19] 9pfs/9p.h: convert Doxygen -> kerneldoc format, Christian Schoenebeck, 2022/03/04
- [PULL 03/19] 9p: darwin: Handle struct stat(fs) differences, Christian Schoenebeck, 2022/03/04
- [PULL 12/19] 9pfs: move qemu_dirent_dup() from osdep -> 9p-util, Christian Schoenebeck, 2022/03/04
- Re: [PULL 00/19] 9p queue 2022-03-04, Peter Maydell, 2022/03/04