Six bytes?

Posted Nov 26, 2010 15:02 UTC (Fri) by cladisch (✭ supporter ✭, #50193)
In reply to: Six bytes? by Ross
Parent article: Ghosts of Unix past, part 3: Unfixable designs

I'd really like to know on what architecture bytes have eleven bits. ;-)

The user and group bits wouldn't make much sense without the corresponding IDs.

Six bytes?

Posted Nov 29, 2010 19:57 UTC (Mon) by Ross (guest, #4065) [Link] (1 responses)

True I fail to multiply 3 by 3 :) So it's nine bits. The suid, sticky, and sgid make it twelve if you count them -- one and a half bytes.

However if you are going to count uid and gid those then it started with 2+2+1.5 = 5.5 bytes (sounds like the count in the article I agree), but it moved to 4+4+1.5 = 9.5 bytes. Since the point was that this was something which can't be changed (and hasn't except for POSIX ACLs which are mostly ignored) I don't think that's what the author meant.

But maybe it's true. He seems to be responding to comment so he can clear it up very easily.

Six bytes?

Posted Nov 29, 2010 21:20 UTC (Mon) by neilbrown (subscriber, #359) [Link]

Yes, that is what I meant.

As you say, permission information only uses 5bytes and 1 bit (setuid etc are not permission bits, they are really the 'type' of the object and so are is some ways more closely related to IF_REG etc). Being that precise in the article would have been excessive I think. It is still true that the permissions were stored in 6 bytes. It is just that some room was left over for file type as well.

POSIX ACLs may well be mostly ignored, but ACLs are still the only direction being explored for making the permission model more complete. My point was simply that they have a storage cost which gets worse quickly, but worse than that it has a serious usability cost.