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Date: Sat, 26 Feb 2005 00:53:49 +0100
From: Kay Sievers <kay.sievers@vrfy.org>
To: Greg KH <greg@kroah.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Symlink /sys/class/block to /sys/block
Message-ID: <20050225235349.GA12485@vrfy.org>
References: <courier.4217CBC9.000027C1@mail.farside.org.uk> <20050222190412.GA23687@suse.de> <courier.421C5047.00003EBA@mail.farside.org.uk> <20050224233458.GB26941@suse.de> <loom.20050225T020954-395@post.gmane.org> <20050225223926.GB28014@kroah.com>
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On Fri, Feb 25, 2005 at 02:39:27PM -0800, Greg KH wrote:
> On Fri, Feb 25, 2005 at 01:35:13AM +0000, Kay Sievers wrote:
> > Greg KH <gregkh <at> suse.de> writes:
> > 
> > > 
> > > On Wed, Feb 23, 2005 at 09:43:35AM +0000, Malcolm Rowe wrote:
> > > > Greg KH writes: 
> > > > 
> > > > >>Following the discussion in [1], the attached patch creates 
> > > > >>/sys/class/block
> > > > >>as a symlink to /sys/block. The patch applies to 2.6.11-rc4-bk7.  
> > > > >>
> > > > >>Please cc: me on any replies - I'm not subscribed to the mailing list. 
> > > > >Hm, your patch is linewrapped, and can't be applied :(
> > > > 
> > > > Bah, and I did send it to myself first, but I guess my mailer un-flowed it 
> > > > for me .  I'll try to find a better mailer. 
> > > > 
> > > > >But more importantly:
> > > > >>static void disk_release(struct kobject * kobj)
> > > > >
> > > > >Did you try to remove a disk (like a usb device) and see what happens
> > > > >here?  Hint, this isn't the proper place to remove the symlink...
> > > > 
> > > > Er, yeah. Oops. 
> > > > 
> > > > *Is* there a sensible place to remove the symlink from, though?  Nobody 
> > > > seems to call subsystem_unregister(&block_subsys), which is the place I'd 
> > > > expect to add a call to, and I can't see anything that's otherwise 
> > > > obvious... 
> > > 
> > > If the subsystem is never unregistered, then don't worry about undoing
> > > the symlink.
> > 
> > This symlink will break a lot of applications out there. If there is not a
> > _very_ good reason for it, we should not do that.
> 
> People seem to want it for some odd reason, I haven't seen a good reason
> yet though, let alone a working patch :)

Good.

> > The "dev" file unfortunately does not tell you if it's a char or block
> > device node and that should be solved by something better than matching a
> > magic string somewhere in the middle of a devpath.
> 
> Use the subsystem value.  If it's "block", it's a block device,
> otherwise it's a char device.  Don't we already do this in udev today?

You don't have any subsystem value if you get a device list from
sysfs, right?

> > The hotplug events will still have the /block/* devpath, so this symlink
> > will give us nothing than problems.
> 
> It will not give hotplug programs issues, as the block devpath still
> remains the same.

No, but anything like udevstart or HAL coldplugging will have a problem
with that inconsistency.

Thanks,
Kay
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