[PATCH] ash: add bash-compatible EPOCH variables

[Denys Vlasenko]

On Tue, Apr 9, 2019 at 9:28 AM Ron Yorston <rmy at pobox.com> wrote:
> Bash 5.0 added the dynamic variable EPOCHSECONDS and EPOCHREALTIME
> which return the number of seconds since the Unix Epoch as an
> integer or float.  These are useful for logging or tracing.

Thanks!
Can you add them to hush too?

> Signed-off-by: Ron Yorston <rmy at pobox.com>
> ---
>  shell/ash.c | 77 ++++++++++++++++++++++++++++++++++++++---------------
>  1 file changed, 56 insertions(+), 21 deletions(-)
>
> diff --git a/shell/ash.c b/shell/ash.c
> index 255d57e62..623ab4103 100644
> --- a/shell/ash.c
> +++ b/shell/ash.c
> @@ -220,6 +220,7 @@
>  #define    BASH_SOURCE          ENABLE_ASH_BASH_COMPAT
>  #define    BASH_PIPEFAIL        ENABLE_ASH_BASH_COMPAT
>  #define    BASH_HOSTNAME_VAR    ENABLE_ASH_BASH_COMPAT
> +#define    BASH_EPOCH_VARS      ENABLE_ASH_BASH_COMPAT
>  #define    BASH_SHLVL_VAR       ENABLE_ASH_BASH_COMPAT
>  #define    BASH_XTRACEFD        ENABLE_ASH_BASH_COMPAT
>  #define    BASH_READ_D          ENABLE_ASH_BASH_COMPAT
> @@ -2053,6 +2054,10 @@ static void changepath(const char *) FAST_FUNC;
>  #if ENABLE_ASH_RANDOM_SUPPORT
>  static void change_random(const char *) FAST_FUNC;
>  #endif
> +#if BASH_EPOCH_VARS
> +static void change_seconds(const char *) FAST_FUNC;
> +static void change_realtime(const char *) FAST_FUNC;
> +#endif
>
>  static const struct {
>         int flags;
> @@ -2079,6 +2084,10 @@ static const struct {
>  #if ENABLE_ASH_RANDOM_SUPPORT
>         { VSTRFIXED|VTEXTFIXED|VUNSET|VDYNAMIC, "RANDOM", change_random },
>  #endif
> +#if BASH_EPOCH_VARS
> +       { VSTRFIXED|VTEXTFIXED|VUNSET|VDYNAMIC, "EPOCHSECONDS", change_seconds },
> +       { VSTRFIXED|VTEXTFIXED|VUNSET|VDYNAMIC, "EPOCHREALTIME", change_realtime },
> +#endif
>  #if ENABLE_LOCALE_SUPPORT
>         { VSTRFIXED|VTEXTFIXED|VUNSET, "LC_ALL"    , change_lc_all   },
>         { VSTRFIXED|VTEXTFIXED|VUNSET, "LC_CTYPE"  , change_lc_ctype },
> @@ -2110,26 +2119,26 @@ extern struct globals_var *BB_GLOBAL_CONST ash_ptr_to_globals_var;
>  #define linenovar     (G_var.linenovar    )
>  #define vifs      varinit[0]
>  #if ENABLE_ASH_MAIL
> -# define vmail    (&vifs)[1]
> -# define vmpath   (&vmail)[1]
> -# define vpath    (&vmpath)[1]
> -#else
> -# define vpath    (&vifs)[1]
> -#endif
> -#define vps1      (&vpath)[1]
> -#define vps2      (&vps1)[1]
> -#define vps4      (&vps2)[1]
> +# define vmail    varinit[1]
> +# define vmpath   varinit[2]
> +#endif
> +#define VAR_OFFSET1 ENABLE_ASH_MAIL*2

To protect from incorrect operator pairing after
macro expansion, use (ENABLE_ASH_MAIL*2)

> +#define vpath     varinit[VAR_OFFSET1 + 1]
> +#define vps1      varinit[VAR_OFFSET1 + 2]
> +#define vps2      varinit[VAR_OFFSET1 + 3]
> +#define vps4      varinit[VAR_OFFSET1 + 4]
>  #if ENABLE_ASH_GETOPTS
> -# define voptind  (&vps4)[1]
> -# define vlineno  (&voptind)[1]
> -# if ENABLE_ASH_RANDOM_SUPPORT
> -#  define vrandom (&vlineno)[1]
> -# endif
> -#else
> -# define vlineno  (&vps4)[1]
> -# if ENABLE_ASH_RANDOM_SUPPORT
> -#  define vrandom (&vlineno)[1]
> -# endif
> +# define voptind  varinit[VAR_OFFSET1 + 5]
> +#endif
> +#define VAR_OFFSET2 VAR_OFFSET1 + ENABLE_ASH_GETOPTS

and here too, use ()

> +#if BASH_EPOCH_VARS
> +static void FAST_FUNC
> +change_epoch(struct var *vepoch, const char *fmt)
> +{
> +       struct timeval tv;
> +       char buffer[32];

It's not immediately clear that 32 is enough.
(It theoretically wouldn't be if/when longs are >64 bits).

How about
  char buffer[sizeof("%lu.nnnnnn") + sizeof(long)*3];

> +       gettimeofday(&tv, NULL);
> +       sprintf(buffer, fmt, tv.tv_sec, tv.tv_usec);

I propose

  sprintf(buffer, fmt, (unsigned long)tv.tv_sec, (unsigned)tv.tv_usec);

(Unsigned long, not signed, because people do not acutely need
to support negative (before epoch) times, whereas people do prefer
their 32-bit systems to overflow and show garbage not in the year 2038,
but in the year 2106).

> +       setvar(vepoch->var_text, buffer, VNOFUNC);
> +       vepoch->flags &= ~VNOFUNC;
> +}
> +
> +static void FAST_FUNC
> +change_seconds(const char *value UNUSED_PARAM)
> +{
> +       change_epoch(&vepochs, "%ld");

"%lu"

> +}
> +
> +static void FAST_FUNC
> +change_realtime(const char *value UNUSED_PARAM)
> +{
> +       change_epoch(&vepochr, "%ld.%06ld");

"%lu.%06u"