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1.5.8.mq_getattr() #
NAME
mq_setattr, mq_getattr – set/get message queue attributes
SYNOPSIS
#include <mqueue.h>
- int mq_setattr(mqd_t mqdes , const struct mq_attr *mqstat,
- struct mq_attr* omqstat );
- int mq_getattr(mqd_t mqdes , struct mq_attr *mqstat );
- struct mq_attr {
- long mq_flags; /* message queue flags */
- long mq_maxmsg; /* maximum number of messages */
- long mq_msgsize; /* maximum message size */
- long mq_curmsgs; /* number of messages currently queued */
- …
- };
DESCRIPTION
mq_setattr() is used to set attributes associated with the message queue specified by mqdes .
The message queue attributes corresponding to the following members defined in the mq_attr structure are set to the specified values upon successful completion of mq_setattr() :
mq_flags The value of this member is either 0 or O_NONBLOCK.
The values of mq_maxmsg , mq_msgsize , and mq_curmsgs are ignored by mq_setattr().
If omqstat is non-NULL, mq_setattr() stores, in the location referenced by omqstat , the previous message queue attributes and the current queue status. These values are the same as would be returned by a call to mq_getattr() at that point. mq_getattr() is used to get status information and attributes associated with the message queue specified in mqdes . Upon return, the mq_flags member of the mq_attr structure referenced by mqstat has the value that was set when the message queue was created but also with modifications made by subsequent mq_setattr() calls.
The following attributes were set at message queue creation:
mq_maxmsg
mq_msgsize
Upon return, the mq_curmsgs (the number of messages currently on the queue) member of the mq_attr structure referenced by mqstat is set according to the current state of the message queue.
RETURN VALUES
Upon successful completion, these function(s) return 0 ; otherwise, they return -1 , and set errno to indicate the error condition.
mq_setattr() , if successful, also changes the attributes of the message queue as specified.
ERRORS
- EBADF
- mqdes is not a valid message queue descriptor.