Path: utzoo!utgpu!water!watmath!clyde!att!occrsh!uokmax!rmtodd
From: rmtodd@uokmax.UUCP (Richard Michael Todd)
Newsgroups: comp.os.minix
Subject: Re: Block special file sizes
Summary: mkfs
Keywords: Block,Special,/dev/fd?
Message-ID: <1622@uokmax.UUCP>
Date: 17 Jul 88 19:51:44 GMT
References: <13@ausonics.OZ>
Reply-To: rmtodd@uokmax.UUCP (Richard Michael Todd)
Organization: University of Oklahoma, Norman, OK
Lines: 25

In article <13@ausonics.OZ> grahams@ausonics.OZ (Graham Stoney) writes:
>Could someone please explain how the /dev block special files are attributed
>with a size?. For example, /dev/fd0 has a size of 360k; but how did it get it?
>mknod(2) has no way of specifying a size; in fact, if you rm /dev/fd0 then
>mknod it again with the same major and minor device numbers, it loses its
>size. How was it created in the first place?.
The only way to create a block-special-file with a size is to specify it
in the prototype file given to mkfs when the system is created.  The
required line in the prototype file looks like this:
	fd0  b--644 2   1   2   0   360
       name   mode  uid gid maj/min size in KB

As you saw, mknod(2) cannot specify the size when the special-file is created.
The whole idea of block-special file *having* a size is unique to MINIX; no 
other Unix variant has it.  It isn't terribly clear to me that it's all that 
useful to have.  I suppose if you were terribly interested (and willing to 
risk major havoc to your filesystem) you could write a program to add a size 
value to an inode created with mknod(2); it obviously requires mucking 
around with the raw device on which the filesystem in question is stored and 
directly fiddling with the inode fields yourself (yecch).  
-- 
Richard Todd	Highly Dubious Domain: rmtodd@uokmax.ecn.uoknor.edu
USSnail:820 Annie Court,Norman OK 73069 	Fido:1:147/1
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