Re: [PATCH] ls: support --time=creation to show/sort birth time

[Assaf Gordon]

Hello Pádraig and all,


On 2020-01-02 10:48 a.m., Pádraig Brady wrote:
> +  ls now supports the --time=birth option to display and sort by
> +  file creation time, where available.

+1

Patch looks good, builds and passes the test on Debian 10/x86_64,
OpenBSD 6.6, FreeBSD 12.1, Alpine Linux, and Cygwin-10/64bit on 
Windows7/NTFS.

A suggestion:

>   static char const *const time_args[] =
>   {
> -  "atime", "access", "use", "ctime", "status", NULL
> +  "atime", "access", "use",
> +  "ctime", "status",
> +  "birth", "creation",
> +  NULL
>   };
>   static enum time_type const time_types[] =
>   {
> -  time_atime, time_atime, time_atime, time_ctime, time_ctime
> +  time_atime, time_atime, time_atime,
> +  time_ctime, time_ctime,
> +  time_btime, time_btime,
>   };

Perhaps add "btime" and "crtime" as aliases to birth time?
"btime" is for completion with atime/ctime.
"crtime" is used/mentioned in some contexts (e.g. in "debugfs").

> +/* Return the platform birthtime member of the stat structure,
> +   or fallback to the mtime member, which we have populated
> +   from the statx structure where supported.  */

Regarding "fall back to mtime", I'm seeing the following results
on some systems - not necessarily a bug, but perhaps it's worth
knowing what to expect:

* Debian 10/x86_64, Linux Kernel 4.19.0, glibc 2.28-10,
with ext2 file system (not supporting birthtime):

  $ ./src/ls -l --time=birth /tmp/dummy-ext2/2
  -rw-r--r-- 1 root root 0 Dec 31  1969 /tmp/dummy-ext2/2

(I guess this is unix-epoch adjusted for my local time zone)


* Alpine Linux, Kernel 4.19.80, musl-libc 1.1.22:

    $ ./src/ls -l --time=birth README
    -rw-r--r-- 1 miles miles 10778            ? README


* OpenBSD 6.6 on "ffs" type file system:

    $ ./src/ls -l --time=birth README
   -rw-r--r-- 1 miles miles 10778            ? README


On all the above systems, running "./src/stat" correctly
shows "birth: -" .

regards,
 - assaf