Programming :: Clarification In The Select System Call?
Dec 8, 2010
I have a process that forks, where the childs puts some data of random size and exits while the parent should get the data and does some manipulation.. here I have used a pipe for child to write the data and parent to read the data.. Child simply dumps the data, and the data is of any size even child and parent doesnt know.
I have used select in the parent to see whether there is any data coming on the reading end of the pipe.. if there is a data.. I copy into a buffer.. Im reading the data continusly when the child exits after closing the writing end of pipe. Parent gets blocked on the read part But my question is how parent know the other of pipe is closed when using the select call. In otherwords.. while using select in readfds, how would i know the other end has closed the pipe..
i wanted to capture the stdout and stdin of a child process within a parent so that any output of child is sent to the parent and any input taken from the parent. code is simple enough and i have followed all code guidlines on the internet (some guidlines do differ also) my select call either hangs if i do not give a tmeout and with a timeout it returns 0 descriptors to be written to or read from:
below is the simple code for parent:
int main(void) { int outfd[2]; int infd[2];
[code].....
why select hangs without a timeout ... why can it not detect that the pipe is write ready i.e parent can write to it ... if it does not detect tha read pipe as having data...
I am trying to figure out how i would go about finding out where system call is made and error checking is not done. I have code below, if somebody can point me in the right direction where system call is made but error checking is not done.Quote:
how to create a new system call Linux? what is the process of creating ?my project is to create a system call for displaying owner of a file..where exactly we have to write the system call code? and where are the places need to change ?
I want to test my system call that be goint to add to kernel, But when i finish compiling kernel, i found my system call code not work. the code i want to return the system time "struct timespec":
/*----------Start of mycall.c----------*/ #include <linux/linkage.h> #include <linux/time.h> #include <linux/kernel.h>
[code]....
so i want a method to test the new system call before compiling kernel.
Anyone know the reason why a sleep( ) on a Redhat Linux OS would cause the system to indefinitely hang? It's doing this every 10 or so calls in my program and I have to press the reboot button on my computer. My program is reading from a UDP port that has messages sent to it 20 times per second. When I sleep I assume the internal UDP buffer is getting more and more filled.
i've written small tool in C which makes measurements on my router (OpenWrt White Russian).
It is working as a deamon. If the tool is started manually, everything works fine. If it is started per script on startup, the following system call doesn't work :
rc = system (command); the returned rc in this case is 256.
first i thought it is a problems with the user rights for the tool, so i have added +s to it. but that didn't help. as i said, when the daemon is started by hand, the system call works fine.
I am making a library, but I am facing a strange problem while sending data over network using ethernet.
I am sending 39 bytes of the data from one server to slave application but some time slave receives 39 bytes and some time it receives 29 bytes. And when ever slave receives 29 bytes all the memories to which my pointers are pointing get changed. This problem is only when I am sending data from the server to slave, while sending data from slave to server I am facing no such issue.
I have a script for dd command and i am using it in an application using system() call. Now i want to have the output of the script file (i.e output of dd command) in the application file itself.
In practice I have a script that call a java program that call a linux system command. The script if I run it, from a shell functions well,so it is not a java problem. The problem come out when i put this script in a crontab schedulation. The result in this case is that java do not execute the system command. I think it depends on crontab
we have a multi threaded program on Linux where one thread is waiting on poll() system call with event set to POLLIN, & another thread has closed the same socket fd (which is passed to poll) , but the poll() did not return, is this the expected behavior? From man page of poll we found that the poll should return POLLNVAL if the socket fd is closed, is my understanding correct or is there any bug in the poll()?In Solaris we observed that the poll system call is returning with POLLNVAL if the socket is closed.
I have the following code: Code: #include <stdio.h> #include <stdlib.h> int main() { system("ps -ef | grep myprocessname"); return 0; }
When I run this program it outputs the following list of running processes: Code: root 10279 10275 0 13:02 ? 00:00:00 myprocessname myvar1=value1 myvar2=value2 root 10341 10337 1 13:02 ? 00:00:00 myprocessname myvar1=value1 myvar2=value2
What I want to really do is instead of writing the output to screen I want to read the output and parse the various values value1, value2 etc. What is the best way to do this?
I'm using gmake (v3.81) to build some c executables. As the first step in the process I run the files through a preprocessor (for embedded SQL). The preprocessor completes successfully, but the gmake reports an error and discontinues buiding the remaining dependencies...
make *** [myfile.c] Error 4
which (according to /usr/include/asm-generic/errno-base.h) means "interrupted System Call". My preprocessor doesn't raise any signals, so I'm not sure what's causing this error.
This is a bit of an odd problem that's been happening to me recently. My home folder is a version of Fedora old, I've been using the same one between Fedora 11 and 12 (which I'm now using).
When booting up, I notice that my system fonts are not the ones I have manually set. They're the ugly version, whatever exact font it is. It's only when I select System->Appearances from the menu that the system seems to detect my seletions to use Liberation fonts in all areas, and then everything instantly switches to the more visually pleasing Liberation fonts. This is a strange bug, I was wondering if anyone has experienced this or can point me in the right direction?
I have currently had the need to go back to basic socket programming, and implemented a simple udp packet sender. But I realized I needed to be able to select which network interface to send the packets from.
The reason is so that one of the interfaces has vlan tagging, and I need my UDP packets to be accordingly vlan tagged. For example, one of the interfaces is eth1.200.
I was wondering if there was a way to add a switch to a gcc/g++ call everytime. I have a few libraries that I need to compile for different processors. Each has a makefile which calls gcc to compile. Here is the best option I could come up with so far:Include a Makefile and define CC as gcc -mcpu=xxx.
having trouble understanding selinux. the domain is cluster containing permissions. a type is nothing more than a label applied to something like a file,right? so instead of applying the permission set of foo domain to the /etc/shadow file it would be apply label shadow_t to /etc/shadow and make the shadow_t apart of the foo domain?
We are seeing some dropped SSH connections because of which some of the process are failing . The main likely reason for the connection drops is that both the client and server remains 100% busy during a certain time interval and during that time interval we see those occassional connection closed by the server.
iam trying to add a system call to the kernel version 2.6.33.7.Iam running fedora 13.I have followed all the steps given in this <hekimian-williams.com/?p=20 -> tutorial,but iam getting a error in make saying undfined reference to mysyscall in syscall_table_32.
what is what is signal 0 in linux system call ?i can't find that in kill -l signal list . i need to know what is signal 0 . * for examples signal 1 is SIGHUP and signal 2 is SIGINIT . what is signal 0 ?
i have only basic knowledge of C so guys plz help me...is C language support call the C executable inside the C ?example contect mainA.c have a many function define in the struct,when i compile mainA and make a executable the name is ( A ),can i use executable C inside the C <my C program call the executable ( A ) > .
I have created a executable file using c and I have also created a GUI using GTK+. Now how can I call the executable file from the GUI with arguments passing to the executable file.
There are examples everywhere about calling f77 subroutine from IDL, but I have not found any material about IDL calling fortran written in f90 way(free style). I tried the following example, but write the subroutines in free style. When I run the makefile, it gives an error 'undefined reference to main_'.
Code:
SUBROUTINE SUM_ARRAY(argc, argv) !Called by IDL INTEGER*4 argc, argv(*) !Argc and Argv are integers j = LOC(argc) !Obtains the number of arguments (argc)
I have a set of iptables rules generated by Firestarter, and i'm in the process of trying to familiarise myself with iptables itself, but there's one particular rule which is confusing me, perhaps somebody could explain it to me
I searched this on the web to no avail. Could I get a clarification on what exactly Yum ,Yumex, and Packager Installer are? Yum is the terminal and Package installer is (System>Addministration>Add/Remove Sofware correct? Additionally what is Yup and what is Yumex.
I seem to be able to install / configure Postfix server in 10 minutes as an MTA for a single domain but my struggle is really understanding the maps / restrictions which even after reading "The Book of Postfix" is not very clear to me:
[Code]....
My question is between those commonly used three maps above, what are the difference between them and how do I know when to use one over the other? Can someone clearly explain them to me? Here's what I have in my 'main.cf' but honestly I couldn't tell you if they're correct or now:
