Re: [PATCH v2 1/2] util: Introduce qemu_get_host_name()

[Daniel P . Berrangé]

On Mon, Jun 22, 2020 at 07:26:44PM +0200, Michal Privoznik wrote:
> This function offers operating system agnostic way to fetch host
> name. It is implemented for both POSIX-like and Windows systems.
> 
> Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
> ---
>  include/qemu/osdep.h | 10 ++++++++++
>  util/oslib-posix.c   | 32 ++++++++++++++++++++++++++++++++
>  util/oslib-win32.c   | 13 +++++++++++++
>  3 files changed, 55 insertions(+)
> 
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index ff7c17b857..a795d46b28 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -607,4 +607,14 @@ static inline void qemu_reset_optind(void)
>  #endif
>  }
>  
> +/**
> + * qemu_get_host_name:
> + * @errp: Error object
> + *
> + * Operating system agnostic way of querying host name.
> + *
> + * Returns allocated hostname (caller should free), NULL on failure.
> + */
> +char *qemu_get_host_name(Error **errp);
> +
>  #endif
> diff --git a/util/oslib-posix.c b/util/oslib-posix.c
> index 916f1be224..865a3d71a7 100644
> --- a/util/oslib-posix.c
> +++ b/util/oslib-posix.c
> @@ -761,3 +761,35 @@ void sigaction_invoke(struct sigaction *action,
>      }
>      action->sa_sigaction(info->ssi_signo, &si, NULL);
>  }
> +
> +#ifndef HOST_NAME_MAX
> +# ifdef _POSIX_HOST_NAME_MAX
> +#  define HOST_NAME_MAX _POSIX_HOST_NAME_MAX
> +# else
> +#  define HOST_NAME_MAX 255
> +# endif
> +#endif
> +
> +char *qemu_get_host_name(Error **errp)
> +{
> +    long len = -1;
> +    char *hostname;
> +
> +#ifdef _SC_HOST_NAME_MAX
> +    len = sysconf(_SC_HOST_NAME_MAX);
> +#endif /* _SC_HOST_NAME_MAX */
> +
> +    if (len < 0) {
> +        len = HOST_NAME_MAX;
> +    }
> +
> +    hostname = g_malloc0(len + 1);

Nitpick, generally qemu prefers g_new0

> +
> +    if (gethostname(hostname, len) < 0) {
> +        error_setg_errno(errp, errno,
> +                         "cannot get hostname");
> +        return NULL;
> +    }

According to my man page, it is undefined by POSIX whether there's a
trailing NUL when  hostname exceeds the buffer, so the paranoid thing
todo is to add

  hostname[len] = '\0';

Regards,
Daniel
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