Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!iuvax!bsu-cs!dhesi
From: dhesi@bsu-cs.bsu.edu (Rahul Dhesi)
Newsgroups: comp.unix.wizards
Subject: Extending a file backwards
Summary: was Re: Releasing blocks from a file
Keywords: extending files backwards at beginning
Message-ID: <7344@bsu-cs.bsu.edu>
Date: 20 May 89 20:20:33 GMT
References: <461@anvil.oz> <508@chudich.co.rmit.oz>
Reply-To: dhesi@bsu-cs.bsu.edu (Rahul Dhesi)
Organization: CS Dept, Ball St U, Muncie, Indiana
Lines: 20

While we are on the subject (sort of), here is another idea.

I want to be able to say

     lseek (fd, (long) -count, 1);
     write (fd, buf, count);

and have it work even if the file pointer is at the beginning of the
file.  This will not be easy to implement.  It will require the
filesystem to add a block to the beginning of the file (easy), and
remember where within that block the file actually starts (harder).

But it could be very useful.  Many programs (e.g. sendmail) spend a lot
of time manipulating headers in a message without touching the body.
My repl command adds a Replied: header as the first line in each
message to which I reply.  Currently these manipulations involve making
a new copy of the message.
-- 
Rahul Dhesi <dhesi@bsu-cs.bsu.edu>
UUCP:    ...!{iuvax,pur-ee}!bsu-cs!dhesi