shmat() with fixed address


 
Thread Tools Search this Thread
Top Forums Programming shmat() with fixed address
# 1  
Old 12-05-2010
shmat() with fixed address

Hi,
I'm using Ubuntu 10.04 on a 64bit machine.

In my shmat() call, I want to assign fixed memory address to shmaddr variable. I have no idea which address value to give. Some where in the net I read we can make use of sysproc info to know the user space addresses, but could not figure out how to get that, please help on this.
void *shmat(int shmid, const void *shmaddr, int shmflg);

Note:
-----
the reason I want to use fixed address is to build linked list on the shmget() returned memory and my other process will map into fixed address and access the linked list.
# 2  
Old 12-05-2010
The problem is that a valid address running one process may not be valid/available in another. In fact, an address that may be valid on one system may not be valid on another system. That's why it is recommended to use an automatic address assignment.

If all of the communicating processes are the same and fork from one program, you can use shmat() before forking and each process will automatically have the memory segment at the same address.

Otherwise, the best course of action is to not use absolute pointers but instead use some for of relative pointer: for example, an integer offset from the base of the segment. Unfortunately, this requires a bit of code to dereference these "pointers".
Login or Register to Ask a Question

Previous Thread | Next Thread

10 More Discussions You Might Find Interesting

1. UNIX for Advanced & Expert Users

C program to detect duplicate ip address if any after assigning ip address to ethernet interface

Hi , Could someone let me know how to detect duplicate ip address after assigning ip address to ethernet interface using c program (3 Replies)
Discussion started by: Gopi Krishna P
3 Replies

2. SuSE

shmat failed due to Cannot allocate memory

Hi, My program was running for a whole night. after 12 hours i got an error message "Cannot allocate memory" during the shmat commmand. So can you please let me know what could be the reason? is there any solution? thanks in advance. Regards, Mano (5 Replies)
Discussion started by: ManoharanMani
5 Replies

3. UNIX for Advanced & Expert Users

Doubt on fixed ip address assinged by dhcp server?

we can assign a dynamic and fixed ip address for a dhcp_client through dhcp server , if it is dynamic ip address , it would be having lease time and renews after half of the leasetime gets over. would the same funda applies for fixed ip address to .. i dont think so ... please confirm on the... (3 Replies)
Discussion started by: Gopi Krishna P
3 Replies

4. Debian

Question on the dhcp-server configuration for a fixed IP address.

Hi , when i configure my server with a fixed ip address in dhcpd.conf as below subnet 172.21.151.0 netmask 255.255.255.0 { range 172.21.151.66 172.21.151.66; } host switch { hardware ethernet 00:05:30:02:DB:31; fixed-address 172.21.151.66; } when i start dhcpd server , it... (2 Replies)
Discussion started by: Gopi Krishna P
2 Replies

5. Programming

Problem shmat in HP-UX Titanium ia64. EINVAL Error

I have a process that needs two active connections to the same zone of shared memory simultaneously. The firs conection works ok, but when i do the second call to shmat it give me error 22 (EINVAL). Only works ok the second call to shmat if i disconnect the first connection (shmdt) Steps:... (3 Replies)
Discussion started by: dairby
3 Replies

6. UNIX for Advanced & Expert Users

Problem shmat in HP-UX. EINVAL Error

I have a process that need two active connections to the same zone of shared memory. But when i do the second call to shmat it give me error 22 (EINVAL). Only works ok the second call to shmat if i disconnect the first connection (shmdt) In Sun,AIX and Digital, i donīt have this problem. ... (7 Replies)
Discussion started by: dairby
7 Replies

7. AIX

sharemem-f-shmat

Hi, I got this error from AIX 4.3.3/db2 7: * %SHAREMEM-F-SHMAT Error getting PUTPARM shared memory address , shmid=23029 * * 3630, errno=13 Anybody who know how to fix this? Thanks in advance, itik (1 Reply)
Discussion started by: itik
1 Replies

8. Linux

shmat() Failure While Using a Large Amount of Shared Memory

Hi, I'm developing a data processing pipeline with multiple stages, with data being moved between the stages using shared memory segments. The size of the data is typically of the order of hundreds of megabytes, and there are typically a few tens of main shared memory segments each of size... (2 Replies)
Discussion started by: theicarusagenda
2 Replies

9. Programming

shmat problem

The first shmat in my program cannot fetch the start address of the shared memory. #include <stdio.h> #include <unistd.h> #include <sys/types.h> #include <sys/ipc.h> #include <sys/shm.h> int main(int argc,char *argv) { int pid; key_t mykey; int shmid; long *shm; long *shm2; ... (3 Replies)
Discussion started by: yong
3 Replies

10. HP-UX

shmat() permission denied, what's this?

I have installed an application that runs correctly for root but not other users. The application generates an error that indicates users don't have permission to attach to shared memory. A daemon process creates the shared memory segment. I've checked every permission I can think of but nothing... (2 Replies)
Discussion started by: km4hr
2 Replies
Login or Register to Ask a Question

Featured Tech Videos