Problem with too big data buffer in DEVCTL

QNX Newsgroups (Archives) qnx.ddk
1

Hello,
it is possible to send data buffer with size about 1MB with using
DEVCTL?
Or how to send such mount of data between resmgr and client?
Thanks
Juraj

2

MsgSend() is used to transfer the data, and the maximum size for
one-part message-pass is 2^32 - 1 (SSIZE_MAX). If you want to avoid
copying the data in the buffer, you can use MsgRead () / MsgWrite ()
to read data from the client’s address.

3

juro <juraj.frank@naex-dot-sk.no-spam.invalid> wrote:

Hello,
it is possible to send data buffer with size about 1MB with using
DEVCTL?

Yes, the API will happily transfer any size of buffer up to the
maximum that can be sent.

Or how to send such mount of data between resmgr and client?

MsgSend() (the underlying kernel call) uses signed 32-bit integers
for message lengths. This suggests the maximum transfer would be
2G – for a devctl() it would be 2G-sizeof(devctl header).

-David

David Gibbs
QNX Training Services
dagibbs@qnx.com

4

async <asreti@gmail-dot-com.no-spam.invalid> wrote:

MsgSend() is used to transfer the data, and the maximum size for
one-part message-pass is 2^32 - 1 (SSIZE_MAX). If you want to avoid
copying the data in the buffer, you can use MsgRead () / MsgWrite ()
to read data from the client’s address.

MsgSend() takes signed ints for the lengths. This suggests 2^31, rather
than 2^32.

-David

David Gibbs
QNX Training Services
dagibbs@qnx.com