Hotplug events for block devices?

Hotplug events for block devices?

[Kevin P. Fleming]

In looking at the boot process of a 2.5.64 kernel (with DEBUG defined in 
drivers/base/hotplug.c), I can see hotplug events for each of my ATA disks as 
they are added to the "ide" bus in sysfs. So far so good.

However, I'd like to be able to receive hotplug events for _all_ block devices, 
regardless of connection type or anything else. In fact, I'd like to receive 
hotplug events for all block device _minors_ as well, so when the kernel scans 
(or receives) partition information that would generate events as well. The 
event would only have to indicate add/remove, "block", and the DEVPATH to the 
device node in sysfs.

Currently, the "whole disk" block devices appear in /sys/block, but the 
partitions don't seem to appear anywhere in sysfs. However, it appears that the 
"block" directory is a sysfs "subsystem", not a class, so no hotplug events are 
generated when the block subsystem adds/removes devices.

How should this be accomplished? Should the "block" subsystem really be a sysfs 
"class"?



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Re: Hotplug events for block devices?

[Greg KH]

On Wed, Mar 12, 2003 at 04:09:52PM -0700, Kevin P. Fleming wrote:
> In looking at the boot process of a 2.5.64 kernel (with DEBUG defined in 
> drivers/base/hotplug.c), I can see hotplug events for each of my ATA disks 
> as they are added to the "ide" bus in sysfs. So far so good.
> 
> However, I'd like to be able to receive hotplug events for _all_ block 
> devices, regardless of connection type or anything else. In fact, I'd like 
> to receive hotplug events for all block device _minors_ as well, so when 
> the kernel scans (or receives) partition information that would generate 
> events as well. The event would only have to indicate add/remove, "block", 
> and the DEVPATH to the device node in sysfs.

Yes, that would be very good, and has been on my list of things to do
for quite some time.

> Currently, the "whole disk" block devices appear in /sys/block, but the 
> partitions don't seem to appear anywhere in sysfs. However, it appears that 
> the "block" directory is a sysfs "subsystem", not a class, so no hotplug 
> events are generated when the block subsystem adds/removes devices.
> 
> How should this be accomplished? Should the "block" subsystem really be a 
> sysfs "class"?

No, that would get pretty messy :)

What needs to happen is for us to get hotplug events for all kobjects in
the system, or possibly all ksets to keep things down to a dull roar.  I
had a patch around here before the last kobject shakeup, but haven't
worked on it since then.  

If you want to work on this, I'd appreciate it.

Hm, in looking at the code, it should probably be done for struct
subsystem objects, which should catch the existing driver core stuff
too...

thanks,

greg k-h


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Re: Hotplug events for block devices?

[Oliver Neukum]

> > However, I'd like to be able to receive hotplug events for _all_ block
> > devices, regardless of connection type or anything else. In fact, I'd
> > like to receive hotplug events for all block device _minors_ as well, so
> > when the kernel scans (or receives) partition information that would
> > generate events as well. The event would only have to indicate
> > add/remove, "block", and the DEVPATH to the device node in sysfs.
>
> Yes, that would be very good, and has been on my list of things to do
> for quite some time.

How do you construct a sensible DEVPATH for iSCSI or nbd ?
How do you notify about the loss or gain of an IO path as opposed
to a whole device?

	Regards
		Oliver



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Re: Hotplug events for block devices?

[Greg KH]

On Thu, Mar 13, 2003 at 01:08:03AM +0100, Oliver Neukum wrote:
> 
> > > However, I'd like to be able to receive hotplug events for _all_ block
> > > devices, regardless of connection type or anything else. In fact, I'd
> > > like to receive hotplug events for all block device _minors_ as well, so
> > > when the kernel scans (or receives) partition information that would
> > > generate events as well. The event would only have to indicate
> > > add/remove, "block", and the DEVPATH to the device node in sysfs.
> >
> > Yes, that would be very good, and has been on my list of things to do
> > for quite some time.
> 
> How do you construct a sensible DEVPATH for iSCSI or nbd ?
> How do you notify about the loss or gain of an IO path as opposed
> to a whole device?

When those device types show up in sysfs, those kinds of problems will
have already been solved.

In other words, not our problem :)

thanks,

greg k-h


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