[systemd-devel] [PATCH v2 2/2] nspawn: skip symlink to a combined cgroup hierarchy if it already exists

[Lennart Poettering]

On Wed, 13.05.15 15:45, Iago López Galeiras (iago at endocode.com) wrote:

> If a symlink to a combined cgroup hierarchy already exists and points to
> the right path, skip it. This avoids an error when the cgroups are set
> manually before calling nspawn.

Thanks! Applied with some minor modifications.

> ---
>  src/nspawn/nspawn.c | 10 ++++++++--
>  src/shared/util.c   | 23 +++++++++++++++++++++++
>  src/shared/util.h   |  1 +
>  3 files changed, 32 insertions(+), 2 deletions(-)
> 
> diff --git a/src/nspawn/nspawn.c b/src/nspawn/nspawn.c
> index f292c63..e9e703f 100644
> --- a/src/nspawn/nspawn.c
> +++ b/src/nspawn/nspawn.c
> @@ -1365,8 +1365,14 @@ static int mount_cgroup(const char *dest) {
>                          if (r < 0)
>                                  return r;
>  
> -                        if (symlink(combined, target) < 0)
> -                                return log_error_errno(errno, "Failed to create symlink for combined hierarchy: %m");
> +                        r = symlink_idempotent(combined, target);
> +                        if (r < 0) {
> +                                if (r == -EINVAL) {
> +                                        log_error("Invalid existing symlink for combined hierarchy");
> +                                        return r;
> +                                } else
> +                                        return log_error_errno(r, "Failed to create symlink for combined hierarchy: %m");
> +                        }
>                  }
>          }
>  
> diff --git a/src/shared/util.c b/src/shared/util.c
> index 466dce4..22e00a6 100644
> --- a/src/shared/util.c
> +++ b/src/shared/util.c
> @@ -2765,6 +2765,29 @@ int symlink_atomic(const char *from, const char *to) {
>          return 0;
>  }
>  
> +int symlink_idempotent(const char *from, const char *to) {
> +        _cleanup_free_ char *p = NULL;
> +        int r;
> +
> +        assert(from);
> +        assert(to);
> +
> +        if (symlink(from, to) < 0) {
> +                if (errno == EEXIST) {
> +                        r = readlink_malloc(to, &p);
> +                        if (r < 0)
> +                                return r;
> +
> +                        if (!streq(p, from)) {
> +                                return -EINVAL;
> +                        }
> +                } else
> +                        return -errno;
> +        }
> +
> +        return 0;
> +}
> +
>  int mknod_atomic(const char *path, mode_t mode, dev_t dev) {
>          _cleanup_free_ char *t = NULL;
>          int r;
> diff --git a/src/shared/util.h b/src/shared/util.h
> index 4a67d5c..8565fd6 100644
> --- a/src/shared/util.h
> +++ b/src/shared/util.h
> @@ -404,6 +404,7 @@ bool machine_name_is_valid(const char *s) _pure_;
>  
>  char* strshorten(char *s, size_t l);
>  
> +int symlink_idempotent(const char *from, const char *to);
>  
>  int symlink_atomic(const char *from, const char *to);
>  int mknod_atomic(const char *path, mode_t mode, dev_t dev);
> -- 
> 2.4.0
> 
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Lennart

-- 
Lennart Poettering, Red Hat