Re: [RFC] lazy allocation of struct block_device

[Richard Gooch]

Alexander Viro writes:
> 
> 
> On Sun, 2 Sep 2001 [e-mail] wrote:
> 
> > That majors allocation is frozen is not my problem.
> > I make life simple with a 64-bit dev_t. Everybody else already has the
> > disadvantages of a 64-bit dev_t, since glibc moves 64 bits around,
> > but not the advantage of a large namespace.
> 
> Not an option for any tree I'd ever run on my box and IIRC Linus was not
> likely to inflict that on his.  As for the glibc...
> 	a) not everything uses this piece of shit

Nod.

> 	b) it would be really nice to get rid of it completely someday

Or at the very least, to selectively not compile large chunks of stuff
that went in that I will never need. Stuff that isn't there on libc5
and other Unices. Something that takes up less than half a floppy.
And having source and binary compatibility between major releases
wouldn't hurt either!

> > Concerning devfs, I don't use it and have not really thought about it.
> > I think my point of view would be that devfs provides a different object.
> > A device node in a filesystem is a pair (pathname, dev_t).
> > Opening it gives the triple (pathname, dev_t, kdev_t).
> > What devfs provides is (pathname), after opening (pathname, kdev_t).
> 
> Wait a second.  To hell with devfs, I'm talking about any synthetic
> tree containing device nodes.  Being forced to allocate a point in
> numeric namespace just to be able to associate a driver-created
> inode with (also driver-created) device...  Looks rather bogus, not
> to mention the ugliness of maintaining said numeric namespace.

Nod.

> > But I think the pointer kdev_t (or i_bcdev) must still be recomputed:
> > it remains true that modules can be unloaded.
> 
> Umm... So what? They can be unloaded only when we have device not opened.
> We might leave both allocation and freeing to driver-side code (and that
> includes grok_partitions()) and let the freeing code reset ->i_bdev and
> friends in all relevant inodes.

Yep. Having to allocate/search for a device structure during open(2)
is insane. It's wasteful. For ext2fs you can do it in lookup(), and
for devfs (or similar) you can do the ideal thing: when the device
entry is registered with the FS (i.e. only once).

				Regards,

					Richard....
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