Re: [9fans] 9fs/9auth for FreeBSD

[Alexander Viro <viro@math.psu.edu>]

On Mon, 2 Apr 2001, Douglas A. Gwyn wrote:

> Alexander Viro wrote:
> > ... I'm not sure that it's the right thing to do, though.
>
> UNIX has always had files that have an innate append-only
> characteristic,
> although it didn't let you specify that a different kind of file should
> be treated as having that characteristic.  The UNIX behavior was that
> write to such a file succeeded, appending to the end of course, and
> seek attempts (to other than the end) would fail.  If some "modern"

Erm. There is a little problem with lseek() returning errors -
reading these files is perfectly sane thing. Pipes et.al. have
innate append-only characteristic, indeed, but append-only regular
files are different - think of that as enforcement (silent or
not - that's where the differences are) of O_APPEND.

> UNIX-like system wants to support user designation of files as having

<shrug> "modern" is a relative term - whether you want to consider
4.4BSD as such or not is a matter of taste, but behaviour in question goes
back at least to '93 (I don't have CVS logs at hand; most likely
the thing was added not just before the release, so s/93/early 90s/)

> an append-only characteristic, then files that have that characteristic
> innately ought to report that the corresponding flag is always set, and
> serve as the model for how I/O is performed.

IIRC, rationale for append-only _inode_ flag (not O_APPEND) was handling
of the logs and similar animals. That's definitely the most frequent
use of that thing. The only real question being: what's better -
complaining about echo foo > append_only_file or silently assuming that
>> was implied.