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[PATCH v5 09/11] 9p: darwin: Implement compatibility for mknodat
From: |
Will Cohen |
Subject: |
[PATCH v5 09/11] 9p: darwin: Implement compatibility for mknodat |
Date: |
Mon, 7 Feb 2022 17:40:22 -0500 |
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 tihs 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
- Move qemu_mknodat from 9p-util to osdep and os-posix]
Signed-off-by: Will Cohen <wwcohen@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
--
2.32.0 (Apple Git-132)
- [PATCH v5 00/11] 9p: Add support for darwin, Will Cohen, 2022/02/07
- [PATCH v5 01/11] 9p: linux: Fix a couple Linux assumptions, Will Cohen, 2022/02/07
- [PATCH v5 04/11] 9p: darwin: Handle struct dirent differences, Will Cohen, 2022/02/07
- [PATCH v5 07/11] 9p: darwin: *xattr_nofollow implementations, Will Cohen, 2022/02/07
- [PATCH v5 02/11] 9p: Rename 9p-util -> 9p-util-linux, Will Cohen, 2022/02/07
- [PATCH v5 03/11] 9p: darwin: Handle struct stat(fs) differences, Will Cohen, 2022/02/07
- [PATCH v5 06/11] 9p: darwin: Move XATTR_SIZE_MAX->P9_XATTR_SIZE_MAX, Will Cohen, 2022/02/07
- [PATCH v5 09/11] 9p: darwin: Implement compatibility for mknodat,
Will Cohen <=
- Re: [PATCH v5 09/11] 9p: darwin: Implement compatibility for mknodat, Christian Schoenebeck, 2022/02/07
- Re: [PATCH v5 09/11] 9p: darwin: Implement compatibility for mknodat, Will Cohen, 2022/02/08
- Re: [PATCH v5 09/11] 9p: darwin: Implement compatibility for mknodat, Christian Schoenebeck, 2022/02/08
- Re: [PATCH v5 09/11] 9p: darwin: Implement compatibility for mknodat, Will Cohen, 2022/02/08
- Re: [PATCH v5 09/11] 9p: darwin: Implement compatibility for mknodat, Christian Schoenebeck, 2022/02/08
- Re: [PATCH v5 09/11] 9p: darwin: Implement compatibility for mknodat, Will Cohen, 2022/02/08
- Re: [PATCH v5 09/11] 9p: darwin: Implement compatibility for mknodat, Will Cohen, 2022/02/08
- Re: [PATCH v5 09/11] 9p: darwin: Implement compatibility for mknodat, Christian Schoenebeck, 2022/02/08
- Re: [PATCH v5 09/11] 9p: darwin: Implement compatibility for mknodat, Christian Schoenebeck, 2022/02/08
- Re: [PATCH v5 09/11] 9p: darwin: Implement compatibility for mknodat, Will Cohen, 2022/02/08