xen-access write protect Error

xen-access write protect Error

[sepanta s]

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Hi,
I am using xen-access to write protect a lot of gfns of the machine, and
listen to each gfn which is going to be written. For each gfn that is
accessed for write operation I create a thread to copy its content after a
short period of time.
I have got the following event as I create a thread for each gfn which is
being written by the user:
error: Could not obtain handle on privileged command interface : Too many
open files
What could cause this as my xen-access program crashes and Segmentation
fault (core dumped) occurs.

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Re: xen-access write protect Error

[Razvan Cojocaru]

> I am using xen-access to write protect a lot of gfns of the machine, and
> listen to each gfn which is going to be written. For each gfn that is
> accessed for write operation I create a thread to copy its content after
> a short period of time.
> I have got the following event as I create a thread for each gfn which
> is being written by the user:
> error: Could not obtain handle on privileged command interface : Too
> many open files
> What could cause this as my xen-access program crashes and Segmentation
> fault (core dumped) occurs.

You're not able to open /dev/xen/privcmd (or /proc/xen/privcmd, see
tools/libs/call/linux.c - I assume you're using Linux), because you have
reached the limit of simultaneously open files that your operating
system will allow.

Try closing some of the handles / files that your application opens.
Even thread handles matter.


HTH,
Razvan

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Re: xen-access write protect Error

[sepanta s]

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Thanks.
I checked my code again to see where I open files but not closing them.
The error was due to opening the xc interface (xc_interface_open()) and not
closing it via xc_interface_close().


On Mon, Sep 12, 2016 at 2:12 PM, Razvan Cojocaru <rcojocaru@bitdefender.com>
wrote:

> > I am using xen-access to write protect a lot of gfns of the machine, and
> > listen to each gfn which is going to be written. For each gfn that is
> > accessed for write operation I create a thread to copy its content after
> > a short period of time.
> > I have got the following event as I create a thread for each gfn which
> > is being written by the user:
> > error: Could not obtain handle on privileged command interface : Too
> > many open files
> > What could cause this as my xen-access program crashes and Segmentation
> > fault (core dumped) occurs.
>
> You're not able to open /dev/xen/privcmd (or /proc/xen/privcmd, see
> tools/libs/call/linux.c - I assume you're using Linux), because you have
> reached the limit of simultaneously open files that your operating
> system will allow.
>
> Try closing some of the handles / files that your application opens.
> Even thread handles matter.
>
>
> HTH,
> Razvan
>

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