This patch adds functionality to request an asynchronous notification
if some other process has send a message to it. We currently send a
SIGALRM to avoid any changes to core infrastructure of signal handling.
Ideally we should implement a separate signal for this. Currently there
is an obvious disadvantage of not being able to use SIGALRM with alarm,
if we are using this functionality.
Currently we only allow users to get and set number of queues. The
operation is always non blocking. There is no provision for non
blocking operation at the moment.
The queue sizes are set to MAX 256 by default. If a user changes the
attributes and sets the queue size or number of messages in a queue
to less than 256, it is the responsibility of the user to close any
queues which were opened with a descriptor greater than the value
currently set.
For example, by default queue sizes are 256. If 150 queues are opened
and then the user sets the number of queues to 32, all open descriptors
and queues from 32 to 150 must be closed. Note that descriptor number
allocation starts with zero and not one.
This commit adds preparatory support for forthcoming message
queue implementation to the Minix kernel. The core implementation
will be added with the next commit.
The entire infrastructure relied on an ACK feature, and as such, it
has been broken for years now, with no easy way to repair it.
Change-Id: I783c2a21276967af115a642199f31fef0f14a572
Sanchayan Maity
