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[Qemu-devel] [PATCH v3 11/13] 9p: darwin: Implement compatibility for mk
From: |
Keno Fischer |
Subject: |
[Qemu-devel] [PATCH v3 11/13] 9p: darwin: Implement compatibility for mknodat |
Date: |
Sat, 16 Jun 2018 20:56:55 -0400 |
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 as an (unexposed in the
C library) system call that sets the cwd for the current thread only.
This should suffice to use mknod safely.
Signed-off-by: Keno Fischer <address@hidden>
---
Changes since v2:
- Silence clang warning for deprecated uses of `syscall`. It is
unforunate that we have to use this depreacted interface, but
there does not seem to be a better option.
hw/9pfs/9p-local.c | 5 +++--
hw/9pfs/9p-util-darwin.c | 31 +++++++++++++++++++++++++++++++
hw/9pfs/9p-util-linux.c | 5 +++++
hw/9pfs/9p-util.h | 2 ++
4 files changed, 41 insertions(+), 2 deletions(-)
diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c
index 56bcabf..450f31c 100644
--- a/hw/9pfs/9p-local.c
+++ b/hw/9pfs/9p-local.c
@@ -668,7 +668,7 @@ 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;
}
@@ -683,7 +683,7 @@ 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;
}
@@ -696,6 +696,7 @@ static int local_mknod(FsContext *fs_ctx, V9fsPath
*dir_path,
err_end:
unlinkat_preserve_errno(dirfd, name, 0);
+
out:
close_preserve_errno(dirfd);
return err;
diff --git a/hw/9pfs/9p-util-darwin.c b/hw/9pfs/9p-util-darwin.c
index ac414bc..194f068 100644
--- a/hw/9pfs/9p-util-darwin.c
+++ b/hw/9pfs/9p-util-darwin.c
@@ -158,3 +158,34 @@ done:
close_preserve_errno(fd);
return ret;
}
+
+#ifndef SYS___pthread_fchdir
+# define SYS___pthread_fchdir 349
+#endif
+
+// This is an undocumented OS X syscall. It would be best to avoid it,
+// but there doesn't seem to be another safe way to implement mknodat.
+// Dear Apple, please implement mknodat before you remove this syscall.
+static int fchdir_thread_local(int fd)
+{
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-declarations"
+ return syscall(SYS___pthread_fchdir, fd);
+#pragma clang diagnostic pop
+}
+
+int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev)
+{
+ int preserved_errno, err;
+ if (fchdir_thread_local(dirfd) < 0) {
+ return -1;
+ }
+ err = mknod(filename, mode, dev);
+ preserved_errno = errno;
+ /* Stop using the thread-local cwd */
+ fchdir_thread_local(-1);
+ if (err < 0) {
+ errno = preserved_errno;
+ }
+ return err;
+}
diff --git a/hw/9pfs/9p-util-linux.c b/hw/9pfs/9p-util-linux.c
index 3902378..06399c5 100644
--- a/hw/9pfs/9p-util-linux.c
+++ b/hw/9pfs/9p-util-linux.c
@@ -63,3 +63,8 @@ int utimensat_nofollow(int dirfd, const char *filename,
{
return utimensat(dirfd, filename, times, AT_SYMLINK_NOFOLLOW);
}
+
+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 b1dc08a..127564d 100644
--- a/hw/9pfs/9p-util.h
+++ b/hw/9pfs/9p-util.h
@@ -90,4 +90,6 @@ ssize_t fremovexattrat_nofollow(int dirfd, const char
*filename,
int utimensat_nofollow(int dirfd, const char *filename,
const struct timespec times[2]);
+int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev);
+
#endif
--
2.8.1
- [Qemu-devel] [PATCH v3 03/13] 9p: darwin: Handle struct stat(fs) differences, (continued)
- [Qemu-devel] [PATCH v3 03/13] 9p: darwin: Handle struct stat(fs) differences, Keno Fischer, 2018/06/16
- [Qemu-devel] [PATCH v3 08/13] 9p: darwin: *xattr_nofollow implementations, Keno Fischer, 2018/06/16
- [Qemu-devel] [PATCH v3 09/13] 9p: darwin: Compatibility for f/l*xattr, Keno Fischer, 2018/06/16
- [Qemu-devel] [PATCH v3 02/13] 9p: Rename 9p-util -> 9p-util-linux, Keno Fischer, 2018/06/16
- [Qemu-devel] [PATCH v3 01/13] 9p: linux: Fix a couple Linux assumptions, Keno Fischer, 2018/06/16
- [Qemu-devel] [PATCH v3 06/13] 9p: darwin: Ignore O_{NOATIME, DIRECT}, Keno Fischer, 2018/06/16
- [Qemu-devel] [PATCH v3 11/13] 9p: darwin: Implement compatibility for mknodat,
Keno Fischer <=
- [Qemu-devel] [PATCH v3 04/13] 9p: darwin: Handle struct dirent differences, Keno Fischer, 2018/06/16
- [Qemu-devel] [PATCH v3 10/13] 9p: darwin: Provide a fallback implementation for utimensat, Keno Fischer, 2018/06/16
- [Qemu-devel] [PATCH v3 13/13] 9p: darwin: configure: Allow VirtFS on Darwin, Keno Fischer, 2018/06/16
- [Qemu-devel] [PATCH v3 12/13] 9p: darwin: virtfs-proxy: Implement setuid code for darwin, Keno Fischer, 2018/06/16
- Re: [Qemu-devel] [PATCH v3 00/13] 9p: Add support for Darwin, no-reply, 2018/06/17