using mq_open to create a new message queue.

[parusasi]

Hi all,
First of all thanks in advance for reading my post and for your heart for helping me.

I am trying to create a message queue using mq_open(name,oflags,mode_t,attr) method. But that function call is returning with an error code EFAULT. By googling it I found that it happens when there is an invalid memory address reference and in another forum it is said that it is because of "internal virtual memory error". Can anybody please help me to get out of this error. Any efforts will be very much appreciated. I am really stuck with that..
Once again thanking you all and waiting for a reply,
regards,
paru.

[jsmith]

Did you look at the man page for mq_open for your system? It should tell you under what conditions
EFAULT occurs.

(I'd help more, but on my system EFAULT is not listed as one of the valid error codes).

[parusasi]

hi Smith,
Thanks for your time.
I checked in the man page. In my man page also EFAULT is not listed. I am not understanding then why it is returning such an error code. Please do help me to clear it out. Thanks again.

[jsmith]

What values are you passing to mq_open?

name must point to a valid C-style string (you could std::cout it)
attr must either be NULL or point to a valid mq_attr struct.

[parusasi]

Hi Smith,
I am calling the method like this. mq_attr is null and thread name is also valid.
mq_open( "/iothreadNewTest", oflags,(S_IRUSR | S_IWUSR),NULL)

Is there any other reasons why it is coming?
Thanks,
Paru

[jsmith]

According to my documentation of mq_open (from the man page), the flags are O_RDONLY, O_WRONLY, and
O_RDWR, but you are using S_IRUSR | S_IWUSR. S_IRUSR | S_IWUSR does not have the same value as
O_RDWR on my linux system, so I'm guessing that's your problem. Try changing your flags to O_RDWR.

[parusasi]

Hi Smith,
for oflags i am giving the values, O_CREAT |O_EXCL. S_IRUSR | S_IWUSR is the value for mode_t.

[jsmith]

Sorry, my bad.

According to the man page, for oflags you must specify exactly one of O_RDONLY, O_WRONLY, or O_RDWR.

[parusasi]

It is ok.. I tried with only one flag also.. but the problem still remains..

[jsmith]

Do I understand that you tried O_RDWR | O_CREAT | O_EXCL for the oflags parameter
or just O_RDWR?

[parusasi]

sorry for not being specific. Since that message queue was not created , i tried O_CREAT first. But then also i got the same error. Then as an experimental thing, i tried with each of these.

[jsmith]

Ok, I'm running out of ideas.

Can you run your program with strace to see what system calls are being executed and with what parameters? (assuming strace is available on your platform)