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• C system calls open / read / write / close problem.

  - by Andrei Ciobanu

  Hello, given the following code (it's supposed to write "hellowolrd" in a "helloworld" file, and then read the text): #include <fcntl.h> #include <sys/types.h> #include <sys/stat.h> #define FNAME "helloworld" int main(){ int filedes, nbytes; char buf[128]; /* Creates a file */ if((filedes=open(FNAME, O_CREAT | O_EXCL | O_WRONLY | O_APPEND, S_IRUSR | S_IWUSR)) == -1){ write(2, "Error1\n", 7); } /* Writes hellow world to file */ if(write(filedes, FNAME, 10) != 10) write(2, "Error2\n", 7); /* Close file */ close(filedes); if((filedes = open(FNAME, O_RDONLY))==-1) write(2, "Error3\n", 7); /* Prints file contents on screen */ if((nbytes=read(filedes, buf, 128)) == -1) write(2, "Error4\n", 7); if(write(1, buf, nbytes) != nbytes) write(2, "Error5\n", 7); /* Close rile afte read */ close(filedes); return (0); } The first time i run the program, the output is: helloworld After that every time I to run the program, the output is: Error1 Error2 helloworld I don't understand why the text isn't appended, as I've specified the O_APPEND file. Is it because I've included O_CREAT ? It the file is already created, shouldn't O_CREAT be ignored ?

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• How can I determine PerlLogHandler performance impact?

  - by Timmy

  I want to create a custom Apache2 log handler, and the template that is found on the apache site is: #file:MyApache2/LogPerUser.pm #--------------------------- package MyApache2::LogPerUser; use strict; use warnings; use Apache2::RequestRec (); use Apache2::Connection (); use Fcntl qw(:flock); use File::Spec::Functions qw(catfile); use Apache2::Const -compile => qw(OK DECLINED); sub handler { my $r = shift; my ($username) = $r->uri =~ m|^/~([^/]+)|; return Apache2::Const::DECLINED unless defined $username; my $entry = sprintf qq(%s [%s] "%s" %d %d\n), $r->connection->remote_ip, scalar(localtime), $r->uri, $r->status, $r->bytes_sent; my $log_path = catfile Apache2::ServerUtil::server_root, "logs", "$username.log"; open my $fh, ">>$log_path" or die "can't open $log_path: $!"; flock $fh, LOCK_EX; print $fh $entry; close $fh; return Apache2::Const::OK; } 1; What is the performance cost of the flocks? Is this logging process done in parallel, or in serial with the HTTP request? In parallel the performance would not matter as much, but I wouldn't want the user to wait another split second to add something like this.

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• Invoking a function (main()) from a binary file in C

  - by Dhara Darji

  I have simple c program like, my_bin.c: #include <stdio.h> int main() { printf("Success!\n"); return 0; } I compile it with gcc and got executable: my_bin. Now I want to invoke main (or run this my_bin) using another C program. That I did with mmap and function pointer like this: #include <stdio.h> #include <fcntl.h> #include <sys/mman.h> int main() { void (*fun)(); int fd; int *map; fd = open("./my_bin", O_RDONLY); map = mmap(0, 8378, PROT_READ, MAP_SHARED, fd, 0); fun = map; fun(); return 0; } PS: I went through some tutorial, for how to read binary file and execute. But this gives Seg fault, any help appreciated! Thanks!

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• C: incompatible types in assignment

  - by The.Anti.9

  I'm writing a program to check to see if a port is open in C. One line in particular copies one of the arguments to a char array. However, when I try to compile, it says: error: incompatible types in assignment Heres the code. The error is on the assignment of addr #include <sys/socket.h> #include <sys/time.h> #include <sys/types.h> #include <arpa/inet.h> #include <netinet/in.h> #include <errno.h> #include <fcntl.h> #include <stdio.h> #include <netdb.h> #include <stdlib.h> #include <string.h> #include <unistd.h> int main(int argc, char **argv) { u_short port; /* user specified port number */ char addr[1023]; /* will be a copy of the address entered by u */ struct sockaddr_in address; /* the libc network address data structure */ short int sock = -1; /* file descriptor for the network socket */ port = atoi(argv[1]); addr = strncpy(addr, argv[2], 1023); bzero((char *)&address, sizeof(address)); /* init addr struct */ address.sin_addr.s_addr = inet_addr(addr); /* assign the address */ address.sin_port = htons(port); /* translate int2port num */ sock = socket(AF_INET, SOCK_STREAM, 0); if (connect(sock,(struct sockaddr *)&address,sizeof(address)) == 0) { printf("%i is open\n", port); } if (errno == 113) { fprintf(stderr, "Port not open!\n"); } close(sock); return 0; } I'm new to C, so I'm not sure why it would do this.

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• C: socket connection timeout

  - by The.Anti.9

  I have a simple program to check if a port is open, but I want to shorten the timeout length on the socket connection because the default is far too long. I'm not sure how to do this though. Here's the code: #include <sys/socket.h> #include <sys/time.h> #include <sys/types.h> #include <arpa/inet.h> #include <netinet/in.h> #include <errno.h> #include <fcntl.h> #include <stdio.h> #include <netdb.h> #include <stdlib.h> #include <string.h> #include <unistd.h> int main(int argc, char **argv) { u_short port; /* user specified port number */ char addr[1023]; /* will be a copy of the address entered by u */ struct sockaddr_in address; /* the libc network address data structure */ short int sock = -1; /* file descriptor for the network socket */ if (argc != 3) { fprintf(stderr, "Usage %s <port_num> <address>", argv[0]); return EXIT_FAILURE; } address.sin_addr.s_addr = inet_addr(argv[2]); /* assign the address */ address.sin_port = htons(atoi(argv[2])); /* translate int2port num */ sock = socket(AF_INET, SOCK_STREAM, 0); if (connect(sock,(struct sockaddr *)&address,sizeof(address)) == 0) { printf("%i is open\n", port); } close(sock); return 0; }

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• C++ Serial Port Only Responding Once Using Write()

  - by Pfeffer

  All the code below works. My device responds, C,7 is a reset. When I run this the second time it doesn't respond. If I manually turn my device off and on, then run this script again it works. But not if I press the button to run the script the second time. RS232: 57600,8,N,1 Any ideas?? Is there any more information needed to solve this? *Also when I get this working I'm going to have to use the read() function to get the devices responses. Does anyone know the correct format I need to use, based on the below code? Sorry I'm new to C++...I'm more of a PHP guy. *I also don't know if 1024 is right, but it seems to work so eh... Thanks so much! #include <termios.h> int fd; struct termios options; fd=open("/dev/tty.KeySerial1", O_RDWR | O_NOCTTY | O_NDELAY); fcntl(fd, F_SETFL, 0); tcgetattr(fd,&options); options.c_ispeed=57600; options.c_ospeed=57600; options.c_cflag |= (CLOCAL | CREAD); options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG); options.c_cflag &= ~CSTOPB; options.c_lflag &= ~ECHO; options.c_oflag &= ~ECHO; options.c_oflag &= ~OPOST; options.c_cflag |= CS8; options.c_cflag |= CRTSCTS; options.c_cc[VMIN] = 0; options.c_cc[VTIME] =10; tcflush(fd, TCIFLUSH); tcsetattr(fd,TCSANOW,&options); write(fd, "C,7\r\n", 1024); close(fd);

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• Why does mmap() fail with ENOMEM on a 1TB sparse file?

  - by metadaddy

  I've been working with large sparse files on openSUSE 11.2 x86_64. When I try to mmap() a 1TB sparse file, it fails with ENOMEM. I would have thought that the 64 bit address space would be adequate to map in a terabyte, but it seems not. Experimenting further, a 1GB file works fine, but a 2GB file (and anything bigger) fails. I'm guessing there might be a setting somewhere to tweak, but an extensive search turns up nothing. Here's some sample code that shows the problem - any clues? #include <errno.h> #include <fcntl.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/mman.h> #include <sys/types.h> #include <unistd.h> int main(int argc, char *argv[]) { char * filename = argv[1]; int fd; off_t size = 1UL << 40; // 30 == 1GB, 40 == 1TB fd = open(filename, O_RDWR | O_CREAT | O_TRUNC, 0666); ftruncate(fd, size); printf("Created %ld byte sparse file\n", size); char * buffer = (char *)mmap(NULL, (size_t)size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); if ( buffer == MAP_FAILED ) { perror("mmap"); exit(1); } printf("Done mmap - returned 0x0%lx\n", (unsigned long)buffer); strcpy( buffer, "cafebabe" ); printf("Wrote to start\n"); strcpy( buffer + (size - 9), "deadbeef" ); printf("Wrote to end\n"); if ( munmap(buffer, (size_t)size) < 0 ) { perror("munmap"); exit(1); } close(fd); return 0; }

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• Using the read function to read in a file.

  - by robUK

  Hello, gcc 4.4.1 I am using the read function to read in a wave file. However, when it gets to the read function. Execution seems to stop and freezes. I am wondering if I am doing anything wrong with this. The file size test-short.wave is: 514K. What I am aiming for is to read the file into the memory buffer chunks at a time. Currently I just testing this. Many thanks for any suggestions, #include <stdio.h> #include <stdlib.h> #include <errno.h> #include <fcntl.h> #include <string.h> #include <unistd.h> int main(void) { char buff = malloc(10240); int32_t fd = 0; int32_t bytes_read = 0; char *filename = "test-short.wav"; /* open wave file */ if((fd = (open(filename, O_RDWR)) == -1)) { fprintf(stderr, "open [ %s ]\n", strerror(errno)); return 1; } printf("Opened file [ %s ]\n", filename); printf("sizeof(buff) [ %d ]\n", sizeof(buff)); printf("strlen(buff) [ %d ]\n", strlen(buff)); bytes_read = read(fd, buff, sizeof(buff)); printf("Bytes read [ %d ]\n", bytes_read); return 0; }

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• 'table' undeclared (first use this in a function)

  - by user2318083

  So I'm not sure why this isn't working, I'm creating a new table and setting it to the variable 'table' Is there something I'm doing wrong? This is the error I get when trying to run it: src/simpleshell.c:19:3: error: ‘table’ undeclared (first use in this function) src/simpleshell.c:19:3: note: each undeclared identifier is reported only once for each function it appears in My code is as follows: #include "parser.h" #include "hash_table.h" #include "variables.h" #include "shell.h" #include <stdio.h> int main(void) { char input[MAXINPUTLINE]; table = Table_create(); signal_c_init(); printf("\nhlsh$ "); while(fgets(input, sizeof(input), stdin)){ stripcrlf(input); parse(input); printf("\nhlsh$ "); } Table_free(table); return 0; } Then this is my create a table in the hash_table file: struct Table *Table_create(void){ struct Table *t; t = (struct Table*)calloc(1, sizeof(struct Table)); return t; } From the hash_table.c: #include "hash_table.h" #include "parser.h" #include "shell.h" #include "variables.h" #include <stdio.h> #include <sys/resource.h> #include <sys/wait.h> #include <sys/types.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <pwd.h> #include <fcntl.h> #include <limits.h> #include <signal.h> struct Table *table; unsigned int hash(const char *x){ int i; unsigned int h = 0U; for (i=0; x[i]!='\0'; i++){ h = h * 65599 + (unsigned char)x[i]; } return h % 1024; }

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• Is it reasonable that a random disk seek & read costs ~16ms?

  - by fzhang

  I am frustrated about the latency of random reading from a non-ssd disk. Based on results from following test program, it speeds ~16 ms for a random read of just 512 bytes without help of os cache. I tried changing 512 to larger values, such as 25k, and the latency did not increase as much. I guess it is because the disk seek dominates the time. I understand that random reading is inherently slow, but just want to be sure that ~16ms is reasonable, even for non-ssd disk. #include <sys/stat.h> #include <sys/time.h> #include <sys/types.h> #include <sys/unistd.h> #include <fcntl.h> #include <limits.h> #include <stdio.h> #include <string.h> int main(int argc, char** argv) { int fd = open(argv[1], O_RDONLY); if (fd < 0) { fprintf(stderr, "Failed open %s\n", argv[1]); return -1; } const size_t count = 512; const off_t offset = 25990611 / 2; char buffer[count] = { '\0' }; struct timeval start_time; gettimeofday(&start_time, NULL); off_t ret = lseek(fd, offset, SEEK_SET); if (ret != offset) { perror("lseek error"); close(fd); return -1; } ret = read(fd, buffer, count); if (ret != count) { fprintf(stderr, "Failed reading all: %ld\n", ret); close(fd); return -1; } struct timeval end_time; gettimeofday(&end_time, NULL); printf("tv_sec: %ld, tv_usec: %ld\n", end_time.tv_sec - start_time.tv_sec, end_time.tv_usec - start_time.tv_usec); close(fd); return 0; }

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• Linux Device Driver: Symbol "memcpy" not found

  - by Hinton

  Hello, I'm trying to write a Linux device driver. I've got it to work really well, until I tried to use "memcpy". I don't even get a compiler error, when I "make" it just warns me: WARNING: "memcpy" [/root/homedir/sv/main.ko] undefined! OK and when I try to load via insmod, I get on the console: insmod: error inserting './main.ko': -1 Unknown symbol in module and on dmesg: main: Unknown symbol memcpy (err 0) I include the following: #include <linux/module.h> #include <linux/moduleparam.h> #include <linux/init.h> #include <linux/kernel.h> /* printk() */ #include <linux/slab.h> /* kmalloc() */ #include <linux/fs.h> /* everything... */ #include <linux/errno.h> /* error codes */ #include <linux/types.h> /* size_t */ #include <linux/fcntl.h> /* O_ACCMODE */ #include <linux/cdev.h> #include <asm/system.h> /* cli(), *_flags */ #include <asm/uaccess.h> /* copy_*_user */ The function using memcpy: static int dc_copy_to_user(char __user *buf, size_t count, loff_t *f_pos, struct sv_data_dev *dev) { char data[MAX_KEYLEN]; size_t i = 0; /* Copy the bulk as long as there are 10 more bytes to copy */ while (i < (count + MAX_KEYLEN)) { memcpy(data, &dev->data[*f_pos + i], MAX_KEYLEN); ec_block(dev->key, data, MAX_KEYLEN); if (copy_to_user(&buf[i], data, MAX_KEYLEN)) { return -EFAULT; } i += MAX_KEYLEN; } return 0; } Could someone help me? I thought the thing was in linux/string.h, but I get the error just the same. I'm using kernel 2.6.37-rc1 (I'm doing in in user-mode-linux, which works only since 2.6.37-rc1). Any help is greatly appreciated. # Context dependent makefile that can be called directly and will invoke itself # through the kernel module building system. KERNELDIR=/usr/src/linux ifneq ($(KERNELRELEASE),) EXTRA_CFLAGS+=-I $(PWD) -ARCH=um obj-m := main.o else KERNELDIR ?= /lib/modules/$(shell uname -r)/build PWD = $(shell pwd) all: $(MAKE) V=1 ARCH=um -C $(KERNELDIR) M=$(PWD) modules clean: rm -rf Module.symvers .*.cmd *.ko .*.o *.o *.mod.c .tmp_versions *.order endif

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• C socket programming: connect() hangs

  - by Fantastic Fourier

  Hey all, I'm about to rip my hair out. I have this client that tries to connect to a server, everything seems to be fine, using gethostbyname(), socket(), bind(), but when trying toconnect()` it just hangs there and the server doesn't see anything from the client. I know that the server works because another client (also in C) can connect just fine. What causes the server to not see this incoming connection? I'm at the end of my wits here. The two different clients are pretty similar too so I'm even more lost. if (argc == 2) { host = argv[1]; // server address } else { printf("plz read the manual\n"); exit(1); } hserver = gethostbyname(host); if (hserver) { printf("host found: %p\n", hserver); printf("host found: %s\n", hserver->h_name ); } else { printf("host not found\n"); exit(1); } bzero((char * ) &server_address, sizeof(server_address)); // copy zeroes into string server_address.sin_family = AF_INET; server_address.sin_addr.s_addr = htonl(hserver->h_addr); server_address.sin_port = htons(SERVER_PORT); bzero((char * ) &client_address, sizeof(client_address)); // copy zeroes into string client_address.sin_family = AF_INET; client_address.sin_addr.s_addr = htonl(INADDR_ANY); client_address.sin_port = htons(SERVER_PORT); sockfd = socket(AF_INET, SOCK_STREAM, 0); if (sockfd < 0) exit(1); else { printf("socket is opened: %i \n", sockfd); info.sock_fd = sockfd; rv = fcntl(sockfd, F_SETFL, O_NONBLOCK); // socket set to NONBLOCK if(rv < 0) printf("nonblock failed: %i %s\n", errno, strerror(errno)); else printf("socket is set nonblock\n"); } timeout.tv_sec = 0; // seconds timeout.tv_usec = 500000; // micro seconds ( 0.5 seconds) setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(struct timeval)); rv = bind(sockfd, (struct sockaddr *) &client_address, sizeof(client_address)); if (rv < 0) { printf("MAIN: ERROR bind() %i: %s\n", errno, strerror(errno)); exit(1); } else printf("socket is bound\n"); rv = connect(sockfd, (struct sockaddr *) &server_address, sizeof(server_address)); printf("rv = %i\n", rv); if (rv < 0) { printf("MAIN: ERROR connect() %i: %s\n", errno, strerror(errno)); exit(1); } else printf("connected\n"); Any thoughts or insights are deeply greatly humongously appreciated. -Fourier

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• Redirecting one file to another using dub2 and strtok

  - by Sergiy Zakharov

  OK, here goes. I have to write a program, in which I need to use strtok and dup2 to redirect one file to another, but I need to also have the user to actually put the command cat < file1 file2, but not from the shell, but instead by using my program. That's why I need strtok. And the reason my program doesn't work is probably because of that, because I don't really understand how strtok works. I found a similar program on the internet, but they just take the ls command and redirect it to the file. That's it. My program is much more complicated. I mean, it would've been easier just to say in shell cat < file1 file2, but for some reason they want us to do it this way. So, anyways, here is what I have so far (here I just combined what I have found on the internet with what I already had from before. We had to do something similar but then the user would just go ls or ls -l. Very simple stuff. This is much harder, for me, at least.) #include <fcntl.h> #include <unistd.h> #include <stdio.h> #include <errno.h> #include <sys/wait.h> #include <string.h> int main() { pid_t pid; char line[256]; char *args[129]; int i; int fd; int status; char *temp; while (1) { printf(">"); if (fgets(line, 256, stdin) == 0) { exit(0); } else { pid = fork(); if (pid == 0) { i = 0; temp = strtok("<",line); while (temp != NULL) { args[i++] = temp; temp = strtok(">",line); args[i] = '\0'; } fd = open("hello", O_RDONLY); dup2(fd, STDIN_FILENO); fd = open("world", O_WRONLY|O_CREAT|O_TRUNC, S_IRWXU); dup2(fd, STDOUT_FILENO ); close(fd); execvp(args[0], args); } else { close(fd); wait(&status); } } } } Any help would be greatly appreciated.

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• C Named pipe (fifo). Parent process gets stuck

  - by Blitzkr1eg

  I want to make a simple program, that fork, and the child writes into the named pipe and the parent reads and displays from the named pipe. The problem is that it enters the parent, does the first printf and then it gets weird, it doesn't do anything else, does not get to the second printf, it just ways for input in the console. #include <string.h> #include <stdlib.h> #include <stdio.h> #include <unistd.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> void main() { char t[100]; mkfifo("myfifo",777); pid_t pid; pid = fork(); if (pid==0) { //execl("fifo2","fifo2",(char*)0); char r[100]; printf("scrie2->"); scanf("%s",r); int fp; fp = open("myfifo",O_WRONLY); write(fp,r,99); close(fp); printf("exit kid \n"); exit(0); } else { wait(0); printf("entered parent \n"); // <- this it prints // whats below this line apparently its not being executed int fz; printf("1"); fz = open("myfifo",O_RDONLY); printf("2"); printf("fd: %d",fz); char p[100]; int size; printf("------"); //struct stat *info; //stat("myfifo",info); printf("%d",(*info).st_size); read(fz,p,99); close(fz); printf("%s",p); printf("exit"); exit(0); } }

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• Bash can't start a programme that's there and has all the right permissions

  - by Rory

  This is a gentoo server. There's a programme prog that can't execute. (Yes the execute permission is set) About the file $ ls prog $ ./prog bash: ./prog: No such file or directory $ file prog prog: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), for GNU/Linux 2.2.5, dynamically linked (uses shared libs), not stripped $ pwd /usr/local/bin $ /usr/local/bin/prog bash: /usr/local/bin/prog: No such file or directory $ less prog | head ELF Header: Magic: 7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 Class: ELF32 Data: 2's complement, little endian Version: 1 (current) OS/ABI: UNIX - System V ABI Version: 0 Type: EXEC (Executable file) Machine: Intel 80386 Version: 0x1 I have a fancy less, to show that it's an actual executable, here's some more data: $ xxd prog |head 0000000: 7f45 4c46 0101 0100 0000 0000 0000 0000 .ELF............ 0000010: 0200 0300 0100 0000 c092 0408 3400 0000 ............4... 0000020: 0401 0a00 0000 0000 3400 2000 0700 2800 ........4. ...(. 0000030: 2600 2300 0600 0000 3400 0000 3480 0408 &.#.....4...4... 0000040: 3480 0408 e000 0000 e000 0000 0500 0000 4............... 0000050: 0400 0000 0300 0000 1401 0000 1481 0408 ................ 0000060: 1481 0408 1300 0000 1300 0000 0400 0000 ................ 0000070: 0100 0000 0100 0000 0000 0000 0080 0408 ................ 0000080: 0080 0408 21f1 0500 21f1 0500 0500 0000 ....!...!....... 0000090: 0010 0000 0100 0000 40f1 0500 4081 0a08 ........@...@... and $ ls -l prog -rwxrwxr-x 1 1000 devs 725706 Aug 6 2007 prog $ ldd prog not a dynamic executable $ strace ./prog 1249403877.639076 execve("./prog", ["./prog"], [/* 27 vars */]) = -1 ENOENT (No such file or directory) 1249403877.640645 dup(2) = 3 1249403877.640875 fcntl(3, F_GETFL) = 0x8002 (flags O_RDWR|O_LARGEFILE) 1249403877.641143 fstat(3, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 0), ...}) = 0 1249403877.641484 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x2b3b8954a000 1249403877.641747 lseek(3, 0, SEEK_CUR) = -1 ESPIPE (Illegal seek) 1249403877.642045 write(3, "strace: exec: No such file or dir"..., 40strace: exec: No such file or directory ) = 40 1249403877.642324 close(3) = 0 1249403877.642531 munmap(0x2b3b8954a000, 4096) = 0 1249403877.642735 exit_group(1) = ? About the server FTR the server is a xen domU, and the programme is a closed source linux application. This VM is a copy of another VM that has the same root filesystem (including this programme), that works fine. I've tried all the above as root and same problem. Did I mention the root filesystem is mounted over NFS. However it's mounted 'defaults,nosuid', which should include execute. Also I am able to run many other programmes from that mounted drive /proc/cpuinfo: processor : 0 vendor_id : GenuineIntel cpu family : 15 model : 4 model name : Intel(R) Xeon(TM) CPU 3.00GHz stepping : 1 cpu MHz : 2992.692 cache size : 1024 KB fpu : yes fpu_exception : yes cpuid level : 5 wp : yes flags : fpu tsc msr pae mce cx8 apic mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm constant_tsc pni monitor ds_cpl cid cx16 xtpr bogmips : 5989.55 clflush size : 64 cache_alignment : 128 address sizes : 36 bits physical, 48 bits virtual power management: Example of a file that I can run I can run other programmes on that mounted filesystem on that server. For example: $ ls -l ls -rwxr-xr-x 1 root root 105576 Jul 25 17:14 ls $ file ls ls: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), for GNU/Linux 2.6.9, dynamically linked (uses shared libs), stripped $ ./ls attr cat cut echo getfacl ln more ... (you get the idea) ... rmdir sort tty $ less ls | head ELF Header: Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 Class: ELF64 Data: 2's complement, little endian Version: 1 (current) OS/ABI: UNIX - System V ABI Version: 0 Type: EXEC (Executable file) Machine: Advanced Micro Devices X86-64 Version: 0x1

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• Apache doesn't run multiple requests

  - by Reinderien

  I'm currently running this simple Python CGI script to test rudimentary IPC: #!/usr/bin/python -u import cgi, errno, fcntl, os, os.path, sys, time print("""Content-Type: text/html; charset=utf-8 <!doctype html> <html lang="en"> <head> <meta charset="utf-8" /> <title>IPC test</title> </head> <body> """) ftempname = '/tmp/ipc-messages' master = not os.path.exists(ftempname) if master: fmode = 'w' else: fmode = 'r' print('<p>Opening file</p>') sys.stdout.flush() ftemp = open(ftempname, fmode) print('<p>File opened</p>') if master: print('<p>Operating as master</p>') sys.stdout.flush() for i in range(10): print('<p>' + str(i) + '</p>') sys.stdout.flush() time.sleep(1) ftemp.close() os.remove(ftempname) else: print('<p>Operating as a slave</p>') ftemp.close() print(""" </body> </html>""") The 'server-push' portion works; that is, for the first request, I do see piecewise updates. However, while the first request is being serviced, subsequent requests are not started, only to be started after the first request has finished. Any ideas on why, and how to fix it? Edit: I see the same non-concurrent behaviour with vanilla PHP, running this: <!doctype html> <html lang="en"> <!-- $Id: $--> <head> <meta charset="utf-8" /> <title>IPC test</title> </head> <body> <p> <?php function echofl($str) { echo $str . "</b>\n"; ob_flush(); flush(); } define('tempfn', '/tmp/emailsync'); if (file_exists(tempfn)) $perms = 'r+'; else $perms = 'w'; assert($fsync = fopen(tempfn, $perms)); assert(chmod(tempfn, 0600)); if (!flock($fsync, LOCK_EX | LOCK_NB, $wouldblock)) { assert($wouldblock); $master = false; } else $master = true; if ($master) { echofl('Running as master.'); assert(fwrite($fsync, 'content') != false); assert(sleep(5) == 0); assert(flock($fsync, LOCK_UN)); } else { echofl('Running as slave.'); echofl(fgets($fsync)); } assert(fclose($fsync)); echofl('Done.'); ?> </p> </body> </html>

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• ls hangs for a certain directory

  - by Jakobud

  There is a particular directory (/var/www), that when I run ls (with or without some options), the command hangs and never completes. There is only about 10-15 files and directories in /var/www. Mostly just text files. Here is some investigative info: [me@server www]$ df . Filesystem Size Used Avail Use% Mounted on /dev/mapper/vg_dev-lv_root 50G 19G 29G 40% / [me@server www]$ df -i . Filesystem Inodes IUsed IFree IUse% Mounted on /dev/mapper/vg_dev-lv_root 3.2M 435K 2.8M 14% / find works fine. Also I can type in cd /var/www/ and press TAB before pressing enter and it will successfully tab-completion list of all files/directories in there: [me@server www]$ cd /var/www/ cgi-bin/ create_vhost.sh html/ manual/ phpMyAdmin/ scripts/ usage/ conf/ error/ icons/ mediawiki/ rackspace sqlbuddy/ vhosts/ [me@server www]$ cd /var/www/ I have had to kill my terminal sessions several times because of the ls hanging: [me@server ~]$ ps | grep ls gdm 6215 0.0 0.0 488152 2488 ? S<sl Jan18 0:00 /usr/bin/pulseaudio --start --log-target=syslog root 23269 0.0 0.0 117724 1088 ? D 18:24 0:00 ls -Fh --color=always -l root 23477 0.0 0.0 117724 1088 ? D 18:34 0:00 ls -Fh --color=always -l root 23579 0.0 0.0 115592 820 ? D 18:36 0:00 ls -Fh --color=always root 23634 0.0 0.0 115592 816 ? D 18:38 0:00 ls -Fh --color=always root 23740 0.0 0.0 117724 1088 ? D 18:40 0:00 ls -Fh --color=always -l me 23770 0.0 0.0 103156 816 pts/6 S+ 18:41 0:00 grep ls kill doesn't seem to have any affect on the processes, even as sudo. What else should I do to investigate this problem? It just randomly started happening today. UPDATE dmesg is a big list of things, mostly related to an external USB HDD that I've mounted too many times and the max mount count has been reached, but that is an un-related problem I think. Near the bottom of dmesg I'm seeing this: INFO: task ls:23579 blocked for more than 120 seconds. "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. ls D ffff88041fc230c0 0 23579 23505 0x00000080 ffff8801688a1bb8 0000000000000086 0000000000000000 ffffffff8119d279 ffff880406d0ea20 ffff88007e2c2268 ffff880071fe80c8 00000003ae82967a ffff880407169ad8 ffff8801688a1fd8 0000000000010518 ffff880407169ad8 Call Trace: [<ffffffff8119d279>] ? __find_get_block+0xa9/0x200 [<ffffffff814c97ae>] __mutex_lock_slowpath+0x13e/0x180 [<ffffffff814c964b>] mutex_lock+0x2b/0x50 [<ffffffff8117a4d3>] do_lookup+0xd3/0x220 [<ffffffff8117b145>] __link_path_walk+0x6f5/0x1040 [<ffffffff8117a47d>] ? do_lookup+0x7d/0x220 [<ffffffff8117bd1a>] path_walk+0x6a/0xe0 [<ffffffff8117beeb>] do_path_lookup+0x5b/0xa0 [<ffffffff8117cb57>] user_path_at+0x57/0xa0 [<ffffffff81178986>] ? generic_readlink+0x76/0xc0 [<ffffffff8117cb62>] ? user_path_at+0x62/0xa0 [<ffffffff81171d3c>] vfs_fstatat+0x3c/0x80 [<ffffffff81258ae5>] ? _atomic_dec_and_lock+0x55/0x80 [<ffffffff81171eab>] vfs_stat+0x1b/0x20 [<ffffffff81171ed4>] sys_newstat+0x24/0x50 [<ffffffff810d40a2>] ? audit_syscall_entry+0x272/0x2a0 [<ffffffff81013172>] system_call_fastpath+0x16/0x1b And also, strace ls /var/www/ spits out a whole BUNCH of information. I don't know what is useful here... The last handful of lines: ioctl(1, SNDCTL_TMR_TIMEBASE or TCGETS, {B38400 opost isig icanon echo ...}) = 0 ioctl(1, TIOCGWINSZ, {ws_row=68, ws_col=145, ws_xpixel=0, ws_ypixel=0}) = 0 stat("/var/www/", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 open("/var/www/", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3 fcntl(3, F_GETFD) = 0x1 (flags FD_CLOEXEC) getdents(3, /* 16 entries */, 32768) = 488 getdents(3, /* 0 entries */, 32768) = 0 close(3) = 0 fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 9), ...}) = 0 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3093b18000 write(1, "cgi-bin conf create_vhost.sh\te"..., 125cgi-bin conf create_vhost.sh error html icons manual mediawiki phpMyAdmin rackspace scripts sqlbuddy usage vhosts ) = 125 close(1) = 0 munmap(0x7f3093b18000, 4096) = 0 close(2) = 0 exit_group(0) = ?

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• How do i change the BIOS boot splash screen?

  - by YumYumYum

  I have a Dell PC which has very ugly and bad luck looking Alien face on every boot. I want to change it or disable it forever, but in Bios they do not have any options. How can i change this from my linux Fedora or ArchLinux which is running now? Tried following does not work. ( http://www.pixelbeat.org/docs/bios/ ) ./flashrom -r firmware.old #save current flash ROM just in case ./flashrom -wv firmware.new #write and verify new flash ROM image Also tried: $ cat c.c #include <stdio.h> #include <inttypes.h> #include <netinet/in.h> #include <stdlib.h> #include <string.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <unistd.h> #define lengthof(x) (sizeof(x)/sizeof(x[0])) uint16_t checksum(const uint8_t* data, int len) { uint16_t sum = 0; int i; for (i=0; i<len; i++) sum+=*(data+i); return htons(sum); } void usage(void) { fprintf(stderr,"Usage: therm_limit [0,50,53,56,60,63,66,70]\n"); fprintf(stderr,"Report therm limit of terminal in BIOS\n"); fprintf(stderr,"If temp specifed, it is changed if required.\n"); exit(EXIT_FAILURE); } #define CHKSUM_START 51 #define CHKSUM_END 109 #define THERM_OFFSET 67 #define THERM_SHIFT 0 #define THERM_MASK (0x7 << THERM_SHIFT) #define THERM_OFF 0 uint8_t thermal_limits[]={0,50,53,56,60,63,66,70}; #define THERM_MAX (lengthof(thermal_limits)-1) #define DEV_NVRAM "/dev/nvram" #define NVRAM_MAX 114 uint8_t nvram[NVRAM_MAX]; int main(int argc, char* argv[]) { int therm_request = -1; if (argc>2) usage(); if (argc==2) { if (*argv[1]=='-') usage(); therm_request=atoi(argv[1]); int i; for (i=0; i<lengthof(thermal_limits); i++) if (thermal_limits[i]==therm_request) break; if (i==lengthof(thermal_limits)) usage(); else therm_request=i; } int fd_nvram=open(DEV_NVRAM, O_RDWR); if (fd_nvram < 0) { fprintf(stderr,"Error opening %s [%m]\n", DEV_NVRAM); exit(EXIT_FAILURE); } if (read(fd_nvram, nvram, sizeof(nvram))==-1) { fprintf(stderr,"Error reading %s [%m]\n", DEV_NVRAM); close(fd_nvram); exit(EXIT_FAILURE); } uint16_t chksum = *(uint16_t*)(nvram+CHKSUM_END); printf("%04X\n",chksum); exit(0); if (chksum == checksum(nvram+CHKSUM_START, CHKSUM_END-CHKSUM_START)) { uint8_t therm_byte = *(uint16_t*)(nvram+THERM_OFFSET); uint8_t therm_status=(therm_byte & THERM_MASK) >> THERM_SHIFT; printf("Current thermal limit: %d°C\n", thermal_limits[therm_status]); if ( (therm_status == therm_request) ) therm_request=-1; if (therm_request != -1) { if (therm_status != therm_request) printf("Setting thermal limit to %d°C\n", thermal_limits[therm_request]); uint8_t new_therm_byte = (therm_byte & ~THERM_MASK) | (therm_request << THERM_SHIFT); *(uint8_t*)(nvram+THERM_OFFSET) = new_therm_byte; *(uint16_t*)(nvram+CHKSUM_END) = checksum(nvram+CHKSUM_START, CHKSUM_END-CHKSUM_START); (void) lseek(fd_nvram,0,SEEK_SET); if (write(fd_nvram, nvram, sizeof(nvram))!=sizeof(nvram)) { fprintf(stderr,"Error writing %s [%m]\n", DEV_NVRAM); close(fd_nvram); exit(EXIT_FAILURE); } } } else { fprintf(stderr,"checksum failed. Aborting\n"); close(fd_nvram); exit(EXIT_FAILURE); } return EXIT_SUCCESS; } $ gcc c.c -o bios # ./bios 16DB

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• Why is syslog so much slower than file IO?

  - by ceving

  I wrote a simple test program to measure the performance of the syslog function. This are the results of my test system: (Debian 6.0.2 with Linux 2.6.32-5-amd64) Test Case Calls Payload Duration Thoughput [] [MB] [s] [MB/s] -------------------- ---------- ---------- ---------- ---------- syslog 200000 10.00 7.81 1.28 syslog %s 200000 10.00 9.94 1.01 write /dev/null 200000 10.00 0.03 343.93 printf %s 200000 10.00 0.13 76.29 The test program did 200000 system calls writing 50 Bytes of data during each call. Why is Syslog more than ten times slower than file IO? This is the program I used to perform the test: #include <fcntl.h> #include <stdio.h> #include <string.h> #include <sys/stat.h> #include <sys/time.h> #include <sys/types.h> #include <syslog.h> #include <unistd.h> const int iter = 200000; const char msg[] = "123456789 123456789 123456789 123456789 123456789"; struct timeval t0; struct timeval t1; void start () { gettimeofday (&t0, (void*)0); } void stop () { gettimeofday (&t1, (void*)0); } void report (char *action) { double dt = (double)t1.tv_sec - (double)t0.tv_sec + 1e-6 * ((double)t1.tv_usec - (double)t0.tv_usec); double mb = 1e-6 * sizeof (msg) * iter; if (action == NULL) printf ("Test Case Calls Payload Duration Thoughput \n" " [] [MB] [s] [MB/s] \n" "-------------------- ---------- ---------- ---------- ----------\n"); else { if (strlen (action) > 20) action[20] = 0; printf ("%-20s %-10d %-10.2f %-10.2f %-10.2f\n", action, iter, mb, dt, mb / dt); } } void test_syslog () { int i; openlog ("test_syslog", LOG_PID | LOG_NDELAY, LOG_LOCAL0); start (); for (i = 0; i < iter; i++) syslog (LOG_DEBUG, msg); stop (); closelog (); report ("syslog"); } void test_syslog_format () { int i; openlog ("test_syslog", LOG_PID | LOG_NDELAY, LOG_LOCAL0); start (); for (i = 0; i < iter; i++) syslog (LOG_DEBUG, "%s", msg); stop (); closelog (); report ("syslog %s"); } void test_write_devnull () { int i, fd; fd = open ("/dev/null", O_WRONLY); start (); for (i = 0; i < iter; i++) write (fd, msg, sizeof(msg)); stop (); close (fd); report ("write /dev/null"); } void test_printf () { int i; FILE *fp; fp = fopen ("/tmp/test_printf", "w"); start (); for (i = 0; i < iter; i++) fprintf (fp, "%s", msg); stop (); fclose (fp); report ("printf %s"); } int main (int argc, char **argv) { report (NULL); test_syslog (); test_syslog_format (); test_write_devnull (); test_printf (); }

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• Macports irssi & perl5 installation issues

  - by Dmitri DB

  Long time reader, first time poster. Big, appreciative thanks for everyone's collective questioning and answering here and at stackoverflow, it's helped me quite a lot over the time I've been learning answers through these sites! Apologies in advance if I didn't search hard enough on posts already up on this site to find out what I could do about this issue, but I thought I'd just reach out for the sake of trying at least once. I've experienced this issue while starting up my macports-installed version of irssi: 13:25 -!- Irssi: Error in script dispatch: 13:25 Can't locate lib.pm in @INC (@INC contains: /opt/local/lib/perl5/site_perl/5.12.4/darwin-multi-2level /opt/local/lib/perl5/site_perl/5.12.4 /opt/local/lib/perl5/vendor_perl/5.12.4/darwin-multi-2level /opt/local/lib/perl5/vendor_perl/5.12.4 /opt/local/lib/perl5/5.12.4/darwin-multi-2level /opt/local/lib/perl5/5.12.4 /opt/local/lib/perl5/site_perl/5.12.3/darwin-multi-2level /opt/local/lib/perl5/site_perl/5.12.3 /opt/local/lib/perl5/site_perl /opt/local/lib/perl5/vendor_perl .) at (eval 18) line 1. 13:25 BEGIN failed--compilation aborted at (eval 18) line 1. 13:25 Huh, strange. I looked into it a bit: [email protected] /opt/local/lib/perl5 ?- find . -name "lib.pm" -ls 14673887 16 -r--r--r-- 1 root admin 6853 25 Jun 23:39 ./5.12.4/darwin-thread-multi- 2level/lib.pm [email protected] /opt/local/lib/perl5 ?- l 5.12.4/darwin-thread-multi-2level total 1864 drwxr-xr-x 55 root admin 1870 28 Jun 19:28 . drwxr-xr-x 158 root admin 5372 28 Jun 19:28 .. -rw-r--r-- 1 root admin 177814 25 Jun 23:39 .packlist drwxr-xr-x 6 root admin 204 28 Jun 19:28 B -r--r--r-- 1 root admin 25714 25 Jun 23:39 B.pm drwxr-xr-x 64 root admin 2176 28 Jun 19:28 CORE drwxr-xr-x 3 root admin 102 28 Jun 19:28 Compress -r--r--r-- 1 root admin 3000 25 Jun 23:39 Config.pm -r--r--r-- 1 root admin 228094 25 Jun 23:39 Config.pod -r--r--r-- 1 root admin 409 25 Jun 23:39 Config_git.pl -r--r--r-- 1 root admin 38759 25 Jun 23:39 Config_heavy.pl -r--r--r-- 1 root admin 21174 25 Jun 23:39 Cwd.pm -r--r--r-- 1 root admin 63535 25 Jun 23:39 DB_File.pm drwxr-xr-x 3 root admin 102 28 Jun 19:28 Data drwxr-xr-x 5 root admin 170 28 Jun 19:28 Devel drwxr-xr-x 4 root admin 136 28 Jun 19:28 Digest -r--r--r-- 1 root admin 25185 25 Jun 23:39 DynaLoader.pm drwxr-xr-x 22 root admin 748 28 Jun 19:28 Encode -r--r--r-- 1 root admin 29731 25 Jun 23:39 Encode.pm -r--r--r-- 1 root admin 6736 25 Jun 23:39 Errno.pm -r--r--r-- 1 root admin 5445 25 Jun 23:39 Fcntl.pm drwxr-xr-x 5 root admin 170 28 Jun 19:28 File drwxr-xr-x 3 root admin 102 28 Jun 19:28 Filter -r--r--r-- 1 root admin 1819 25 Jun 23:39 GDBM_File.pm drwxr-xr-x 4 root admin 136 28 Jun 19:28 Hash drwxr-xr-x 3 root admin 102 28 Jun 19:28 I18N drwxr-xr-x 11 root admin 374 28 Jun 19:28 IO -r--r--r-- 1 root admin 1404 25 Jun 23:39 IO.pm drwxr-xr-x 6 root admin 204 28 Jun 19:28 IPC drwxr-xr-x 4 root admin 136 28 Jun 19:28 List drwxr-xr-x 4 root admin 136 28 Jun 19:28 MIME drwxr-xr-x 3 root admin 102 28 Jun 19:28 Math -r--r--r-- 1 root admin 2519 25 Jun 23:39 NDBM_File.pm -r--r--r-- 1 root admin 4208 25 Jun 23:39 O.pm -r--r--r-- 1 root admin 15563 25 Jun 23:39 Opcode.pm -r--r--r-- 1 root admin 21011 25 Jun 23:39 POSIX.pm -r--r--r-- 1 root admin 58962 25 Jun 23:39 POSIX.pod drwxr-xr-x 5 root admin 170 28 Jun 19:28 PerlIO -r--r--r-- 1 root admin 2515 25 Jun 23:39 SDBM_File.pm drwxr-xr-x 4 root admin 136 28 Jun 19:28 Scalar -r--r--r-- 1 root admin 10837 25 Jun 23:39 Socket.pm -r--r--r-- 1 root admin 41003 25 Jun 23:39 Storable.pm drwxr-xr-x 4 root admin 136 28 Jun 19:28 Sys drwxr-xr-x 3 root admin 102 28 Jun 19:28 Text drwxr-xr-x 5 root admin 170 28 Jun 19:28 Time drwxr-xr-x 3 root admin 102 28 Jun 19:28 Unicode -r--r--r-- 1 root admin 14462 25 Jun 23:39 attributes.pm drwxr-xr-x 38 root admin 1292 28 Jun 19:28 auto -r--r--r-- 1 root admin 19892 25 Jun 23:39 encoding.pm -r--r--r-- 1 root admin 6853 25 Jun 23:39 lib.pm -r--r--r-- 1 root admin 11044 25 Jun 23:39 mro.pm -r--r--r-- 1 root admin 997 25 Jun 23:39 ops.pm -r--r--r-- 1 root admin 13945 25 Jun 23:39 re.pm drwxr-xr-x 3 root admin 102 28 Jun 19:28 threads -r--r--r-- 1 root admin 33283 25 Jun 23:39 threads.pm So, it sort of seems to me that the permissions which perl5 got installed with for these modules has gotten mixed up somehow? I'm not really a perl user beyond enjoying it for massive directory-recursive find/replace operations within text files, so I haven't much of an idea what the permissions here are supposed to look like, and I'm not really sure how to go about determining how macports has gone and installed perl this way when it's otherwise worked without failure for years now. Does anyone have any recommendations for the sanest path towards rectifying this issue? Also, is there any interesting reason as to why the macports default for the perl5 port installs 5.12.4, and not 5.16.0, which has to be explicitly installed via the perl5.16 port? Thanks again!

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• Reciving UDP packets on iPhone

  - by Eli

  I'm trying to establish UDP communication between a MAC OS and an iPod through Wi-Fi, at this point I'm able to send packets from the iPod and I can see those packets have the right MAC and ip addresses (I'm using wireshark to monitor the network) but the MAC receives the packets only when the wireshark is on, otherwise recvfrom() returns -1. When I try to transmit from MAC to iPhone I have the same result, I can see the packets are sent but the iPhone doesn't seem to get them. I'm using the next code to send: struct addrinfo hints; int rv; memset(&hints, 0, sizeof hints); hints.ai_family = AF_UNSPEC; hints.ai_socktype = SOCK_DGRAM; if ((rv = getaddrinfo(IP, SERVERPORT, &hints, &servinfo)) != 0) { fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv)); return 1; } // loop through all the results and make a socket for(p = servinfo; p != NULL; p = p->ai_next) { if ((sockfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol)) == -1) { perror("talker: socket"); continue; } break; } if (p == NULL) { fprintf(stderr, "talker: failed to bind socket\n"); return 2; } while (cond) sntBytes += sendto(sockfd, message, strlen(message), 0, p->ai_addr, p->ai_addrlen); return 0; and this code to receive: struct addrinfo hints, *p; int rv; memset(&hints, 0, sizeof hints); hints.ai_family = AF_UNSPEC; // set hints.ai_socktype = SOCK_DGRAM; hints.ai_flags = AI_PASSIVE; // use to AF_INET to force IPv4 my IP if ((rv = getaddrinfo(NULL, MYPORT, &hints, &servinfo)) != 0) { fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv)); return 1; } // loop through all the results and bind to the first we can for(p = servinfo; p != NULL; p = p->ai_next) { if ((sockfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol)) == -1) { perror("listener: socket"); continue; } if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) { close(sockfd); perror("listener: bind"); continue; } break; } if (p == NULL) { fprintf(stderr, "listener: failed to bind socket\n"); return 2; } addr_len = sizeof their_addr; fcntl(sockfd, F_SETFL,O_NONBLOCK); int rcvbuf_size = 128 * 1024; // That's 128Kb of buffer space. setsockopt(sockfd, SOL_SOCKET, SO_RCVBUF, &rcvbuf_size, sizeof(rcvbuf_size)); printf("listener: waiting to recvfrom...\n"); while (cond) rcvBytes = recvfrom(sockfd, buf, MAXBUFLEN-1 , 0, (struct sockaddr *)&their_addr, &addr_len); return 0; What am I missing?

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• How to use pipes for nonblocking IPC (UART emulation)

  - by codebauer

  I would like to write some test/emulation code that emulates a serial port connection. The real code looks like this: DUT <- UART - testtool.exe My plan is to use create a test application (CodeUnderTest.out) on linux that forks to launch testool.out with two (read & write) named pipes as arguments. But I cannot figure out how to make all the pipe IO non-blocking! The setup would look like this:. CodeUnderTest.out <- named pipes - testTool.out (lauched from CodeUnderTest.out) I have tried opening the pipes as following: open(wpipe,O_WRONLY|O_NONBLOCK); open(rpipe,O_RDONLY|O_NONBLOCK); But the write blocks until the reader opens the wpipe. Next I tried the following: open(wpipe,O_RDWR|O_NONBLOCK); open(rpipe,O_RDONLY|O_NONBLOCK); But then the reader of the first message never gets any data (doesn't block though) I also tried adding open and close calls around each message, but that didn't work either... Here is some test code: #include <stdio.h> #include <sys/types.h> #include <unistd.h> #include <fcntl.h> pid_t pid; char* rpipe, *wpipe,*x; FILE *rh,*wh; int rfd,wfd; void openrpipe( void ) { rfd = open(rpipe,O_RDONLY|O_NONBLOCK); rh = fdopen(rfd,"rb"); printf("%sopeningr %x\n",x,rh); } void openwpipe( void ) { //Fails when reader not already opened //wfd = open(wpipe,O_WRONLY|O_NONBLOCK); wfd = open(wpipe,O_RDWR|O_NONBLOCK); wh = fdopen(wfd,"wb"); printf("%sopeningw %x\n",x,wh); } void closerpipe( void ) { int i; i = fclose(rh); printf("%sclosingr %d\n",x,i); } void closewpipe( void ) { int i; i = fclose(wh); printf("%sclosingw %d\n",x,i); } void readpipe( char* expect, int len) { char buf[1024]; int i=0; printf("%sreading\n",x); while(i==0) { //printf("."); i = fread(buf,1,len,rh); } printf("%sread (%d) %s\n",x,i,buf); } void writepipe( char* data, int len) { int i,j; printf("%swriting\n",x); i = fwrite(data,1,len,rh); j = fflush(rh); //No help! printf("%sflush %d\n",x,j); printf("%swrite (%d) %s\n",x,i,data); } int main(int argc, char **argv) { rpipe = "readfifo"; wpipe = "writefifo"; x = ""; pid = fork(); if( pid == 0) { wpipe = "readfifo"; rpipe = "writefifo"; x = " "; openrpipe(); openwpipe(); writepipe("paul",4); readpipe("was",3); writepipe("here",4); closerpipe(); closewpipe(); exit(0); } openrpipe(); openwpipe(); readpipe("paul",4); writepipe("was",3); readpipe("here",4); closerpipe(); closewpipe(); return( -1 ); } BTW: To use the testocd above you need to pipes in the cwd: mkfifo ./readfifo mkfifo ./writefifo

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• Problem with script to add/delete from database

  - by Jason

  Ok - the user enters a product code, price and name using a form - the script then either adds it to the database or deletes it from the database. If the user is trying to delete a product that is not in the database they get a error message. Upon successful adding/deleting they also get a message. However, when I test it - I just get a blank page. Perl doesnt come up with any warnings, syntax errors or anything - says everything is fine... but I still just get a blank page. The script... #!/usr/bin/perl #c09ex5.cgi - saves data to and removes data from a database print "Content-type: text/html\n\n"; use CGI qw(:standard); use SDBM_File; use Fcntl; use strict; #declare variables my ($code, $name, $price, $button, $codes, $names, $prices); #assign values to variables $code = param('Code'); $name = param('Name'); $price = param('Price'); $button = param('Button'); ($code, $name, $price) = format_input(); ($codes, $names, $prices) = ($code, $name, $price); if ($button eq "Save") { add(); } elsif ($button eq "Delete") { remove(); } exit; sub format_input { $codes =~ s/^ +//; $codes =~ s/ +$//; $codes =~ tr/a-z/A-Z/; $codes =~ tr/ //d; $names =~ s/^ +//; $names =~ s/ +$//; $names =~ tr/ //d; $names = uc($names); $prices =~ s/^ +//; $prices =~ s/ +$//; $prices =~ tr/ //d; $prices =~ tr/$//d; } sub add { #declare variable my %candles; #open database, format and add record, close database tie(%candles, "SDBM_File", "candlelist", O_CREAT|O_RDWR, 0666) or die "Error opening candlelist. $!, stopped"; format_vars(); $candles{$codes} = "$names,$prices"; untie(%candles); #create web page print "<HTML>\n"; print "<HEAD><TITLE>Candles Unlimited</TITLE></HEAD>\n"; print "<BODY>\n"; print "<FONT SIZE=4>Thank you, the following product has been added.<BR>\n"; print "Candle: $codes $names $prices</FONT>\n"; print "</BODY></HTML>\n"; } #end add sub remove { #declare variables my (%candles, $msg); tie(%candles, "SDBM_File", "candlelist", O_RDWR, 0) or die "Error opening candlelist. $!, stopped"; format_vars(); #determine if the product is listed if (exists($candles{$codes})) { delete($candles{$codes}); $msg = "The candle $codes $names $prices has been removed."; } else { $msg = "The product you entered is not in the database"; } #close database untie(%candles); #create web page print "<HTML>\n"; print "<HEAD><TITLE>Candles Unlimited</TITLE></HEAD>\n"; print "<BODY>\n"; print "<H1>Candles Unlimited</H1>\n"; print "$msg\n"; print "</BODY></HTML>\n"; }

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• Why do I get a blank page from my Perl CGI script?

  - by Jason

  The user enters a product code, price and name using a form. The script then either adds it to the database or deletes it from the database. If the user is trying to delete a product that is not in the database they get a error message. Upon successful adding or deleting they also get a message. However, when I test it I just get a blank page. Perl doesnt come up with any warnings, syntax errors or anything; says everything is fine, but I still just get a blank page. The script: #!/usr/bin/perl #c09ex5.cgi - saves data to and removes data from a database print "Content-type: text/html\n\n"; use CGI qw(:standard); use SDBM_File; use Fcntl; use strict; #declare variables my ($code, $name, $price, $button, $codes, $names, $prices); #assign values to variables $code = param('Code'); $name = param('Name'); $price = param('Price'); $button = param('Button'); ($code, $name, $price) = format_input(); ($codes, $names, $prices) = ($code, $name, $price); if ($button eq "Save") { add(); } elsif ($button eq "Delete") { remove(); } exit; sub format_input { $codes =~ s/^ +//; $codes =~ s/ +$//; $codes =~ tr/a-z/A-Z/; $codes =~ tr/ //d; $names =~ s/^ +//; $names =~ s/ +$//; $names =~ tr/ //d; $names = uc($names); $prices =~ s/^ +//; $prices =~ s/ +$//; $prices =~ tr/ //d; $prices =~ tr/$//d; } sub add { #declare variable my %candles; #open database, format and add record, close database tie(%candles, "SDBM_File", "candlelist", O_CREAT|O_RDWR, 0666) or die "Error opening candlelist. $!, stopped"; format_vars(); $candles{$codes} = "$names,$prices"; untie(%candles); #create web page print "<HTML>\n"; print "<HEAD><TITLE>Candles Unlimited</TITLE></HEAD>\n"; print "<BODY>\n"; print "<FONT SIZE=4>Thank you, the following product has been added.<BR>\n"; print "Candle: $codes $names $prices</FONT>\n"; print "</BODY></HTML>\n"; } #end add sub remove { #declare variables my (%candles, $msg); tie(%candles, "SDBM_File", "candlelist", O_RDWR, 0) or die "Error opening candlelist. $!, stopped"; format_vars(); #determine if the product is listed if (exists($candles{$codes})) { delete($candles{$codes}); $msg = "The candle $codes $names $prices has been removed."; } else { $msg = "The product you entered is not in the database"; } #close database untie(%candles); #create web page print "<HTML>\n"; print "<HEAD><TITLE>Candles Unlimited</TITLE></HEAD>\n"; print "<BODY>\n"; print "<H1>Candles Unlimited</H1>\n"; print "$msg\n"; print "</BODY></HTML>\n"; }

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• C - Error with read() of a file, storage in an array, and printing output properly

  - by ns1

  I am new to C, so I am not exactly sure where my error is. However, I do know that the great portion of the issue lies either in how I am storing the doubles in the d_buffer (double) array or the way I am printing it. Specifically, my output keeps printing extremely large numbers (with around 10-12 digits before the decimal point and a trail of zeros after it. Additionally, this is an adaptation of an older program to allow for double inputs, so I only really added the two if statements (in the "read" for loop and the "printf" for loop) and the d_buffer declaration. I would appreciate any input whatsoever as I have spent several hours on this error. #include <stdio.h> #include <fcntl.h> #include <sys/types.h> #include <unistd.h> #include <string.h> struct DataDescription { char fieldname[30]; char fieldtype; int fieldsize; }; /* ----------------------------------------------- eof(fd): returns 1 if file `fd' is out of data ----------------------------------------------- */ int eof(int fd) { char c; if ( read(fd, &c, 1) != 1 ) return(1); else { lseek(fd, -1, SEEK_CUR); return(0); } } void main() { FILE *fp; /* Used to access meta data */ int fd; /* Used to access user data */ /* ---------------------------------------------------------------- Variables to hold the description of the data - max 10 fields ---------------------------------------------------------------- */ struct DataDescription DataDes[10]; /* Holds data descriptions for upto 10 fields */ int n_fields; /* Actual # fields */ /* ------------------------------------------------------ Variables to hold the data - max 10 fields.... ------------------------------------------------------ */ char c_buffer[10][100]; /* For character data */ int i_buffer[10]; /* For integer data */ double d_buffer[10]; int i, j; int found; printf("Program for searching a mini database:\n"); /* ============================= Read in meta information ============================= */ fp = fopen("db-description", "r"); n_fields = 0; while ( fscanf(fp, "%s %c %d", DataDes[n_fields].fieldname, &DataDes[n_fields].fieldtype, &DataDes[n_fields].fieldsize) > 0 ) n_fields++; /* --- Prints meta information --- */ printf("\nThe database consists of these fields:\n"); for (i = 0; i < n_fields; i++) printf("Index %d: Fieldname `%s',\ttype = %c,\tsize = %d\n", i, DataDes[i].fieldname, DataDes[i].fieldtype, DataDes[i].fieldsize); printf("\n\n"); /* --- Open database file --- */ fd = open("db-data", O_RDONLY); /* --- Print content of the database file --- */ printf("\nThe database content is:\n"); while ( ! eof(fd) ) { /* ------------------ Read next record ------------------ */ for (j = 0; j < n_fields; j++) { if ( DataDes[j].fieldtype == 'I' ) read(fd, &i_buffer[j], DataDes[j].fieldsize); if ( DataDes[j].fieldtype == 'F' ) read(fd, &d_buffer[j], DataDes[j].fieldsize); if ( DataDes[j].fieldtype == 'C' ) read(fd, &c_buffer[j], DataDes[j].fieldsize); } double d; /* ------------------ Print it... ------------------ */ for (j = 0; j < n_fields; j++) { if ( DataDes[j].fieldtype == 'I' ) printf("%d ", i_buffer[j]); if ( DataDes[j].fieldtype == 'F' ) d = d_buffer[j]; printf("%lf ", d); if ( DataDes[j].fieldtype == 'C' ) printf("%s ", c_buffer[j]); } printf("\n"); } printf("\n"); printf("\n"); } Post edits output: 16777216 0.000000 107245694331284094976.000000 107245694331284094976.000000 Pi 33554432 107245694331284094976.000000 2954938175610156848888276006519501238173891974277081114627768841840801736306392481516295906896346039950625609765296207682724801406770458881439696544971142710292689518104183685723154223544599940711614138798312668264956190761622328617992192.000000 2954938175610156848888276006519501238173891974277081114627768841840801736306392481516295906896346039950625609765296207682724801406770458881439696544971142710292689518104183685723154223544599940711614138798312668264956190761622328617992192.000000 Secret Key 50331648 2954938175610156848888276006519501238173891974277081114627768841840801736306392481516295906896346039950625609765296207682724801406770458881439696544971142710292689518104183685723154223544599940711614138798312668264956190761622328617992192.000000 -0.000000 -0.000000 The number E Expected Output: 3 rows of data ending with the number "e = 2.18281828" To reproduce the problem, the following two files need to be in the same directory as the lookup-data.c file: - db-data - db-description

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