I'm currently studying IPC, I have a first program
A: Do an exec for B and wait
B: Receive through a fifo a string from a third program "C" and have to resend it to A
I was thinking to open a pipe in A before the exec, then passing fd[1] to B as an argument
Then in B:
My problem now is reading this string in A. I was thinking to send a SIGUSR1 to A as soon as the string is written by B on the pipe and having in A something like:
However what I get is *"Error reading len: Success"* , what's wrong ?
Sorry if my English is bad, any help is appreciated, thanks!
I have a parent that is passing data to child A and then child A has to process it and pass to child B. I am able to pass the data to child A but am not able to pass it to child B. Child B seems to only be receiving the last data instead of the whole data.
I saw one example in a book but it uses... (1 Reply)
Hello all,
My problem is as follows:
I'm trying to wake up a select(...); using a pipe fd. This should be rather straightforward, but I cannot get it to work. Perhaps you guys could give me a few tips.
My wakeup function looks like this:
STATIC void net_trig_wr()
{
/* write a dummy... (0 Replies)
Hi All,
I am facing a vague issue while trying to make two process talk to each
other using named pipe.
read process
=========
The process which reads, basically creates FIFO using
mkfifo - ret_val = mkfifo(HALF_DUPLEX, 0666);) func.
It then opens the pipe using open func - fd =... (1 Reply)
Hi All,
I am facing a vague issue while trying to make two process talk to each
other using named pipe.
read process
=========
The process which reads, basically creates FIFO using
mkfifo - ret_val = mkfifo(HALF_DUPLEX, 0666) func.
It then opens the pipe using open func - fd = open... (2 Replies)
Hi,
I´m having a lot of problems when working with message queues, both on HP-UX Systems and Sun Solaris. When we fill a queue with a messages, the system hangs and locks everything that relies on the use of IPC resources. Anyone knows how to eliminate this problem?
Thanks,
Haroldo Teixeira (2 Replies)
Hi guys, I'm new to Linux and Unix I have just simple code . But I don't know why it doesn't work ..
But, the outputfile is Blank.. I don't understand why.. Please help me.. Thank you very much
P.S: sorry, I don't know how to edit this post clearly.. it's hard to read.. Please try.. (2 Replies)
Hi all,
Is there a situation like system assigning same ID's for semaphores and shared memory at the same time.
Ex: When I try to create 10 Shared memory objects with starting key as 0x1500 and 10 semaphore objects with starting key as 0x1234 in the same program. Assume those are not deleted... (2 Replies)
I was asked to look into a problem with a Sun Netra 440 in another department. On the server in question, the relevant 'uname -a' information is, "SunOS host1 5.9 Generic_118558-16 sun4u sparc SUNW,Netra-440". That information aside, while the other admin is logged into the ALOM, these errors are... (0 Replies)
Hi guys,
I need to know how i can ignore Pipe '|' if Pipe is coming as a column in Pipe delimited file
for eg:
file 1:
xx|yy|"xyz|zzz"|zzz|12...
using below awk command
awk 'BEGIN {FS=OFS="|" } print $3
i would get xyz
But i want as :
xyz|zzz to consider as whole column... (13 Replies)
Discussion started by: rohit_shinez
13 Replies
LEARN ABOUT LINUX
copy_file_range
COPY_FILE_RANGE(2) Linux Programmer's Manual COPY_FILE_RANGE(2)NAME
copy_file_range - Copy a range of data from one file to another
SYNOPSIS
#define _GNU_SOURCE
#include <unistd.h>
ssize_t copy_file_range(int fd_in, loff_t *off_in,
int fd_out, loff_t *off_out,
size_t len, unsigned int flags);
DESCRIPTION
The copy_file_range() system call performs an in-kernel copy between two file descriptors without the additional cost of transferring data
from the kernel to user space and then back into the kernel. It copies up to len bytes of data from file descriptor fd_in to file descrip-
tor fd_out, overwriting any data that exists within the requested range of the target file.
The following semantics apply for off_in, and similar statements apply to off_out:
* If off_in is NULL, then bytes are read from fd_in starting from the file offset, and the file offset is adjusted by the number of bytes
copied.
* If off_in is not NULL, then off_in must point to a buffer that specifies the starting offset where bytes from fd_in will be read. The
file offset of fd_in is not changed, but off_in is adjusted appropriately.
The flags argument is provided to allow for future extensions and currently must be to 0.
RETURN VALUE
Upon successful completion, copy_file_range() will return the number of bytes copied between files. This could be less than the length
originally requested.
On error, copy_file_range() returns -1 and errno is set to indicate the error.
ERRORS
EBADF One or more file descriptors are not valid; or fd_in is not open for reading; or fd_out is not open for writing; or the O_APPEND
flag is set for the open file description (see open(2)) referred to by the file descriptor fd_out.
EFBIG An attempt was made to write a file that exceeds the implementation-defined maximum file size or the process's file size limit, or
to write at a position past the maximum allowed offset.
EINVAL Requested range extends beyond the end of the source file; or the flags argument is not 0.
EIO A low-level I/O error occurred while copying.
EISDIR fd_in or fd_out refers to a directory.
ENOMEM Out of memory.
ENOSPC There is not enough space on the target filesystem to complete the copy.
EXDEV The files referred to by file_in and file_out are not on the same mounted filesystem.
VERSIONS
The copy_file_range() system call first appeared in Linux 4.5, but glibc 2.27 provides a user-space emulation when it is not available.
CONFORMING TO
The copy_file_range() system call is a nonstandard Linux and GNU extension.
NOTES
If file_in is a sparse file, then copy_file_range() may expand any holes existing in the requested range. Users may benefit from calling
copy_file_range() in a loop, and using the lseek(2) SEEK_DATA and SEEK_HOLE operations to find the locations of data segments.
copy_file_range() gives filesystems an opportunity to implement "copy acceleration" techniques, such as the use of reflinks (i.e., two or
more inodes that share pointers to the same copy-on-write disk blocks) or server-side-copy (in the case of NFS).
EXAMPLE
#define _GNU_SOURCE
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <unistd.h>
/* On versions of glibc before 2.27, we must invoke copy_file_range()
using syscall(2) */
static loff_t
copy_file_range(int fd_in, loff_t *off_in, int fd_out,
loff_t *off_out, size_t len, unsigned int flags)
{
return syscall(__NR_copy_file_range, fd_in, off_in, fd_out,
off_out, len, flags);
}
int
main(int argc, char **argv)
{
int fd_in, fd_out;
struct stat stat;
loff_t len, ret;
if (argc != 3) {
fprintf(stderr, "Usage: %s <source> <destination>
", argv[0]);
exit(EXIT_FAILURE);
}
fd_in = open(argv[1], O_RDONLY);
if (fd_in == -1) {
perror("open (argv[1])");
exit(EXIT_FAILURE);
}
if (fstat(fd_in, &stat) == -1) {
perror("fstat");
exit(EXIT_FAILURE);
}
len = stat.st_size;
fd_out = open(argv[2], O_CREAT | O_WRONLY | O_TRUNC, 0644);
if (fd_out == -1) {
perror("open (argv[2])");
exit(EXIT_FAILURE);
}
do {
ret = copy_file_range(fd_in, NULL, fd_out, NULL, len, 0);
if (ret == -1) {
perror("copy_file_range");
exit(EXIT_FAILURE);
}
len -= ret;
} while (len > 0);
close(fd_in);
close(fd_out);
exit(EXIT_SUCCESS);
}
SEE ALSO lseek(2), sendfile(2), splice(2)Linux 2019-03-06 COPY_FILE_RANGE(2)