[Xen-users] Re: blktap limited to 100 devices?

["Carl Jones" <carl.jones@xxxxxxxxx>]

Replying to myself here...

Actually setting these work just fine:

# grep 256 linux-2.6.18.8-xen/drivers/xen/blktap/blktap.c
#define MAX_TAP_DEV 256    /*the maximum number of tapdisk ring devices    */
#define MAX_DEV_NAME 256   /*the max tapdisk ring device name e.g. blktap0 */
# grep 256 tools/blktap/lib/blktaplib.h
#define MAX_TAP_DEV 256

Tested against 3.1.4.

Regards,
Carl

On Fri, Jun 13, 2008 at 1:03 PM, Carl Jones <carl.jones@xxxxxxxxx> wrote:

Hi,

Is blktap is limited to 100 devices? My simple test is to have 51 domUs, each with 2 disks attached using tap:aio.

All start up fine except #51:

XENBUS: Timeout connecting to device: device/vbd/51713 (state 3)
XENBUS: Timeout connecting to device: device/vbd/51721 (state 3)
XENBUS: Device with no driver: device/console/0
Root-NFS: No NFS server available, giving up.
VFS: Unable to mount root fs via NFS, trying floppy.
VFS: Cannot open root device "xvda1" or unknown-block(2,0)
Please append a correct "root=" boot option; here are the available partitions:
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(2,0)

On the host I see: tapdisk /var/run/tap/tapctrlwrite1 /var/run/tap/tapctrlread1 to 100, but nothing further.

With 3.1.4 I see these set, but changing them and rebuilding does not help:
./linux-2.6.18.8-xen/drivers/xen/blktap/blktap.c:#define MAX_TAP_DEV 256     /*the maximum number of tapdisk ring devices    */
./linux-2.6.18.8-xen/drivers/xen/blktap/blktap.c:#define MAX_DEV_NAME 100    /*the max tapdisk ring device name e.g. blktap0 */

Is there an easy way around this limit?

Using Xen 3.0.4, 3.1.4 and 3.2.1 (from source) with the same results. Host OS is CentOS 5 64bit.

Regards,
Carl

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