lkml.org 
[lkml]   [1998]   [Aug]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: DEVFSv50 and /dev/fb? (or /dev/fb/? ???)
On Tue, Aug 11, 1998 at 05:12:30PM -0400, Theodore Y. Ts'o wrote:

> My preference would be to store the inodes in the filesystem. If you're
> going to be using a user mode daemon anyway, as you've suggested in
> other mail messages, then let's define a well-defined interface for the
> kernel to notify the user mode daemon that new devices has apeeared
> (either at boot time or due to a PCMCIA/USB/1384 device getting
> inserted), so that the user mode daemon can create the devices as
> necessary.

A well defined interface accompanied by a library that allows `smart'
applications to obtain useful information about devices and media
would be really great.

Especially if this API is able to handle removable media and devices
moving about (which I think is quite doable).

Having a unified API for finding, mounting, and unmouting devices
based on humanly recognisable tokens would be great, and optionally
other information such as a device/media history database might make
backup programs easier to deal with too (assuming the backup program
uses this `smart' API).

I looked at implementing something `smart' for mount(8) a while back,
but couldn't think of a good way to make it compatible with
/etc/fstab and getmntent(3). Arguably, we could just drop backwards
compatibility, as /etc/fstab and getmntent(3) aren't defined by
Unix98, but since most unix like OSs have this in some shape of form
I don't know how reasonable that is.

> Performance won't be an issue, since if the user-mode daemon is
> automatically creating the devices, you won't have "8 million
> devices" in /dev (despite that favoriate devfs strawman argument).
> True, lookups will still have to go through /dev, but the dcache
> pretty much obviates that argument. (Also consider that opening
> devices is generally in the noise as far as most applications are
> concerned. It's hardly a common case that we need to optimize.)

I was about to as how often to devices actually get opened anyhow? I
would thing even on busy systems you could count the number of times
you access by device per hour on one hand. On most systems, only a
limited number of users and applications will use device inodes.

Sure, there are some exceptions, such as mtools and hfstools, (any
others?), but if your doing lots of access then you may as well mount
the filesystem...

One last comment... devfs aside, if your are running off RO media,
how would you handle PCMCIA/USB/1384? (Or is this a silly question?)




-cw

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.altern.org/andrebalsa/doc/lkml-faq.html

\
 
 \ /
  Last update: 2005-03-22 13:43    [W:0.305 / U:0.020 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site