* Re: usb race possible?
2005-06-14 13:35 usb race possible? Andreas Jellinghaus
@ 2005-06-14 14:22 ` Kay Sievers
2005-06-15 13:33 ` Andreas Jellinghaus
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: Kay Sievers @ 2005-06-14 14:22 UTC (permalink / raw)
To: linux-hotplug
On Tue, Jun 14, 2005 at 03:35:59PM +0200, Andreas Jellinghaus wrote:
> Hi,
>
> if a new usb device is added the kernel
> generates a hotplug event including the
> path to the usb device.
>
> does the kernel guarantee that the device
> in the usb device filesystem is available
> when the hotplug script is called?
>
> I have one user here where it seems that
> sometimes the process started via hotplug
> is too fast, i.e. open on the usb device
> fails. manualy running lsusb shows the
> device. linux kernel 2.6.11 (-gentoo,
> not sure what they changed).
>
> so could this be a race condition? any other
> idea how I can debug the issue? for now I added
> a "sleep 1" to the hotplug handler before the
> open and it seems to cure the problem.
That is ok, you need to wait in userspace for the files to show up.
It's not easy to fix in the kernel. Maybe we will get there some day...
Kay
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^ permalink raw reply [flat|nested] 6+ messages in thread* Re: usb race possible?
2005-06-14 13:35 usb race possible? Andreas Jellinghaus
2005-06-14 14:22 ` Kay Sievers
@ 2005-06-15 13:33 ` Andreas Jellinghaus
2005-06-15 14:28 ` Greg KH
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: Andreas Jellinghaus @ 2005-06-15 13:33 UTC (permalink / raw)
To: linux-hotplug
On Tuesday 14 June 2005 16:22, Kay Sievers wrote:
> That is ok, you need to wait in userspace for the files to show up.
> It's not easy to fix in the kernel. Maybe we will get there some day...
do you think "sleep 1" is good enough?
or do I need to implement a full scale
open&retry solution?
Andreas
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^ permalink raw reply [flat|nested] 6+ messages in thread* Re: usb race possible?
2005-06-14 13:35 usb race possible? Andreas Jellinghaus
2005-06-14 14:22 ` Kay Sievers
2005-06-15 13:33 ` Andreas Jellinghaus
@ 2005-06-15 14:28 ` Greg KH
2005-06-15 14:32 ` Andreas Jellinghaus
2005-06-15 22:04 ` Greg KH
4 siblings, 0 replies; 6+ messages in thread
From: Greg KH @ 2005-06-15 14:28 UTC (permalink / raw)
To: linux-hotplug
On Wed, Jun 15, 2005 at 03:33:40PM +0200, Andreas Jellinghaus wrote:
> On Tuesday 14 June 2005 16:22, Kay Sievers wrote:
> > That is ok, you need to wait in userspace for the files to show up.
> > It's not easy to fix in the kernel. Maybe we will get there some day...
>
> do you think "sleep 1" is good enough?
Try it and find out :)
> or do I need to implement a full scale
> open&retry solution?
If you want it to always work on all machines, yes.
Good luck,
greg k-h
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: usb race possible?
2005-06-14 13:35 usb race possible? Andreas Jellinghaus
` (2 preceding siblings ...)
2005-06-15 14:28 ` Greg KH
@ 2005-06-15 14:32 ` Andreas Jellinghaus
2005-06-15 22:04 ` Greg KH
4 siblings, 0 replies; 6+ messages in thread
From: Andreas Jellinghaus @ 2005-06-15 14:32 UTC (permalink / raw)
To: linux-hotplug
On Wednesday 15 June 2005 16:28, Greg KH wrote:
> On Wed, Jun 15, 2005 at 03:33:40PM +0200, Andreas Jellinghaus wrote:
> > On Tuesday 14 June 2005 16:22, Kay Sievers wrote:
> > > That is ok, you need to wait in userspace for the files to show up.
> > > It's not easy to fix in the kernel. Maybe we will get there some day...
> >
> > do you think "sleep 1" is good enough?
>
> Try it and find out :)
>
> > or do I need to implement a full scale
> > open&retry solution?
>
> If you want it to always work on all machines, yes.
ok thanks.
<evil question>
but wouldn't it be better if the hotplug system did that,
instead of putting the same code into every application?
my app is simply called with the device path to handle,
so I feel like it shouldn't do such retry stuff, but rather
the caller should make sure, that the file given as argument
exists...
so maybe put the sleep/wait functionality into the hotplug
core?
</evil>
Regards, Andreas
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^ permalink raw reply [flat|nested] 6+ messages in thread* Re: usb race possible?
2005-06-14 13:35 usb race possible? Andreas Jellinghaus
` (3 preceding siblings ...)
2005-06-15 14:32 ` Andreas Jellinghaus
@ 2005-06-15 22:04 ` Greg KH
4 siblings, 0 replies; 6+ messages in thread
From: Greg KH @ 2005-06-15 22:04 UTC (permalink / raw)
To: linux-hotplug
On Wed, Jun 15, 2005 at 04:32:00PM +0200, Andreas Jellinghaus wrote:
> On Wednesday 15 June 2005 16:28, Greg KH wrote:
> > On Wed, Jun 15, 2005 at 03:33:40PM +0200, Andreas Jellinghaus wrote:
> > > On Tuesday 14 June 2005 16:22, Kay Sievers wrote:
> > > > That is ok, you need to wait in userspace for the files to show up.
> > > > It's not easy to fix in the kernel. Maybe we will get there some day...
> > >
> > > do you think "sleep 1" is good enough?
> >
> > Try it and find out :)
> >
> > > or do I need to implement a full scale
> > > open&retry solution?
> >
> > If you want it to always work on all machines, yes.
>
> ok thanks.
>
> <evil question>
> but wouldn't it be better if the hotplug system did that,
> instead of putting the same code into every application?
We used to have code that did that, look at the old udev releases.
"wait_for_sysfs" was what it was called. Turned out that just putting
that logic into udev was easier :)
So, just put yourself into /etc/dev.d/ or in a udev rule and you should
be fine and not have to do the hotplug wait logic.
hope this helps,
greg k-h
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^ permalink raw reply [flat|nested] 6+ messages in thread