Re: Meaning of size of /dev/pts/ files

[Robert Elz <kre%munnari.OZ.AU@localhost>]

    Date:        Mon, 25 Sep 2023 09:42:36 +0200
    From:        rockyhotas%firemail.cc@localhost
    Message-ID:  <1354f06f549eb36716bca02777cb7bcf%firemail.cc@localhost>

  | The /dev/pts/ files seem to have each their own size, as if they were
  | regular files.

Everything which has an inode (or equivalent) has a size (everything
that stat() can be applied to must have one, as a size field is in the
resulting structure).

  | First curious fact: `ls -l' doesn't show the size in
  | bytes of such files (for some reason).

Because it is meaningless nothing.   POSIX says (in the definition of
the <sys/stat.h> header:

off_t st_size  For regular files, the file size in bytes.
               For symbolic links, the length in bytes of the
               pathname contained in the symbolic link.
               For a shared memory object, the length in bytes.
               For a typed memory object, the length in bytes.
               For other file types, the use of this field is
               unspecified.

The final sentence is the relevant one.

  | Instead, `exa' shows their sizes:

RVP already indicated how you misinterpreted that.

  | So, second curious fact: the sizes of these pts files are not
  | related to the number of characters received by them as output of some
  | command.

Not curious, what you're looking at isn't the size field.

  | Any clue about what these sizes actually represent?

RVP answered that for what you're looking at, the actual size, which is
in the stat() results (which applications should always simply ignore for
anything which isn't a regular file, symlink, or one of the memory types,
as it is unspecified - and which both ls and exa (whatever that is) are
doing, correctly, is irrelevant (and as RVP indicated, should always be
0, as nothing ever sets it to anything different).   Terminal type devices
don't get bigger (which is what the size represents) as you write data to
them, they just pass the data through to someplace else, and forget it.
They do tend to count how much they processed, but that's not a size, and
is terminal dependant data, so not available via stat() (so ls will certainly
never tell you that number).

kre