resmgr_msgget()

Updated: May 06, 2022

Read a message from a client, from local data, or both

Synopsis:

#include <sys/resmgr.h>

ssize_t resmgr_msgget( resmgr_context_t * const ctp,
                        void *msg,
                        size_t size,
                        size_t offset );

Arguments:

ctp
A pointer to a resmgr_context_t structure that the resource manager library uses to pass context information between functions. This function extracts the rcvid and other message-related parameters from this structure.
msg
A pointer to a buffer where the function can store the data.
size
The number of bytes that you want to read. These functions don't let you read past the end of the thread's message; they return the number of bytes actually read.
offset
An offset into the current message that indicates where you want to start reading the data. The offset referenced by ctp cannot be included in this parameter.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The resmgr_msgget() function is a convenience function that you can use in a resource manager instead of resmgr_msgread() or MsgRead().

Based on the requested data offset, this function first copies data from the current local message buffer (if applicable) and then gets the rest of the data (if applicable) from the client by calling MsgRead().

Because combine message offsets are automatically handled, the caller does not add the offset that ctp references to the passed in offset. The passed in offset is just the offset from the start of the current message being processed.

For combine messages (those with the _IO_COMBINE_FLAG set), the amount of data returned to the caller is limited to the size found in the size parameter referenced by ctp. This limit ensures that the caller does not get data from a subsequent message by mistake.

For more information, see Layers in a resource manager in the Bones of a Resource Manager chapter of Writing a Resource Manager.

Returns:

The number of bytes read, or -1 if an error occurs (errno is set).

Errors:

EDEADLK
A deadlock occurred. You can avoid a deadlock by setting the _NTO_CHF_MSG_PAUSING flag when you create a channel; for more information, see ChannelCreate() and MsgPause().
EFAULT
A fault occurred in a server's address space when the kernel tried to access the server's message buffers.
ESRCH
The thread indicated by ctp->rcvid doesn't exist, is no longer REPLY-blocked on the channel, or the connection was detached.
ESRVRFAULT
A fault occurred when the kernel tried to access the buffers provided.
ETIMEDOUT
A kernel timeout unblocked the call. See TimerTimeout().

Classification:

QNX Neutrino

Safety:  
Cancellation point No
Interrupt handler No
Signal handler Yes
Thread Yes