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

[Pádraig Brady]

On 02/01/2020 22:34, Assaf Gordon wrote:
> Hello,
>
> On 2020-01-02 2:01 p.m., Pádraig Brady wrote:
> > On 02/01/2020 20:29, Assaf Gordon wrote:
> > > 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
> > Hmm. That suggests that STATX_BTIME is set in the
> > returned statx mask, but populated with 0 in the structure
> > ({-1,-1} would have printed as '?').

> Indeed, the returned "btime" is zero:

> $ strace -v -e trace=statx ./src/ls -l --time=birth /tmp/dummy-ext2/2
> statx(AT_FDCWD, "/tmp/dummy-ext2/2",
> AT_STATX_SYNC_AS_STAT|AT_SYMLINK_NOFOLLOW,
> STATX_MODE|STATX_NLINK|STATX_UID|STATX_GID|STATX_SIZE|STATX_BTIME,
> {stx_mask=STATX_BASIC_STATS, stx_blksize=1024, stx_attributes=0,
> stx_nlink=1, stx_uid=0, stx_gid=0, stx_mode=S_IFREG|0644, stx_ino=12,
> stx_size=0, stx_blocks=0,
> stx_attributes_mask=STATX_ATTR_COMPRESSED|STATX_ATTR_IMMUTABLE|STATX_ATTR_APPEND|STATX_ATTR_NODUMP|STATX_ATTR_ENCRYPTED,
> stx_atime={tv_sec=1577995860, tv_nsec=0} /* 2020-01-02T13:11:00-0700 */,
> stx_btime={tv_sec=0, tv_nsec=0}, stx_ctime={tv_sec=1577995860,

> Looking closer at the new ls.c code (** are added for emphasis):

> **    if (mask & STATX_BTIME)
>
>           st->st_mtim = statx_timestamp_to_timespec (stx.stx_btime);
>
> **   else if (want_btime)
>
>           st->st_mtim.tv_sec = st->st_mtim.tv_nsec = -1;


> Wouldn't "mask & STATX_BTIME" always be the same as "want_btime",
> resulting in the "else if" part never to be executed?
>
> IIUC, "mask" is the requested bitmask.

Right of course.
Fixed that up locally to:

  if (stx.stx_mask & STATX_BTIME)
    st->st_mtim = statx_timestamp_to_timespec (stx.stx_btime);
  else if (want_btime)
    st->st_mtim.tv_sec = st->st_mtim.tv_nsec = -1;

thanks!
Pádraig