On Montag, 7. Februar 2022 23:40:22 CET Will Cohen wrote:
> From: Keno Fischer <k...@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 <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>
> ---
Like already mentioned by me moments ago on previous v4 (just echoing) ...
> 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
