Basically a file descriptor table is a kernel mantained array of pointers to kernel objects representing open files of some kind.
Imagine for a moment that these were C++ object...
Code:
int read(int fd,char *buf,size_t len)
{
return fds[fd]->read(buf,len);
}
int write(int fd,char *buf,size_t len)
{
return fds[fd]->write(buf,len);
}
int close(int fd,char *buf,size_t len)
{
fds[fd]->close();
fds[fd]=NULL;
}
But as kernels are generally written in C, other mechanisms, (pointers to jump tables etc) are used to provide the polymorphism.
Also reference counting is heavily used, so "close" for instance only really drops a reference count, if it gets to zero then the true close occurs.
What you need to consider in the model is where flags such as whether a file descriptor is blocking or not, and where the file-offset should live. Ask yourself, if I use "dup()" do both file descriptors have the same file offset?
If you do look inside the Linux kernel for instance you will notice that the BSD sockets API is handled quite differently to normal ioctl/read/write.
Ok, I'm sure this is a total newbie question, but I think I'm in the right place, no?
I'm trying to call a perl module from a cgi script - Mail::Sendmail - and my web host installed the module in a directory that doesn't seem to be accessible, at least not the way I'm trying. But I thought you... (1 Reply)
I am trying to find a way to check the current status of a file. Such as some cron job processes are dependent on the completion of others. if a file is currently being accessed / modified or simply open state I will wait until it is done being processed before attempting the next process on that... (3 Replies)
Hi,
look at the following code:
The client after estabilishing a connection with the server does the following:
if ((peter = fopen(argv, "r")) == NULL){
printf("errore\n");
exit(0);
}
... (11 Replies)
I have a requirement to close all the file descriptors from 3 to 1024 for a particular application.
Right now, this is how I do it ..
for ( int i = 3 ; i <= 1024; ++i )
close(i);
The change I am looking at is, I want to do away with the number 1024 and replace it with a constant which... (4 Replies)
I am trying to right a function which uses a file descriptor to write to a log file. The problem is that the on the print statement the file descriptor is called bad. Now when I first open the file and print to it in the f_open function by passing the descriptor to f_print_log all works well,... (6 Replies)
Hello All,
Im opening a file desciptor in perl and sending data using print CMD "$xyz".
is there a limit to the length of the string that I can give to this CMD at a time. (3 Replies)
Hello,
How can i use file descriptor in a script to read 2 files at the same time and extract line 200 from file 1 and line 500 from file 2.
Thanks. (6 Replies)
Hi,
I am trying to read a file line-by-line in a while loop, and perform some tasks which involves non-interactive SSH to a remote server. The code looks something like this --
#!/usr/bin/ksh
export myFile=/path/to/my/file.load
while read line
do
do something
## Adding the SSH... (2 Replies)
Discussion started by: Subu1987
2 Replies
LEARN ABOUT DEBIAN
rangecheck
rangecheck(3) Library Functions Manual rangecheck(3)NAME
rangecheck.h - pointer range checking
SYNTAX
#include <rangecheck.h>
int range_validbuf(const void* buf,size_t len);
int range_ptrinbuf(const void* buf,size_t len,const void* ptr);
int range_bufinbuf(const void* buf1,size_t len1,
const void* buf2,size_t len2);
int range_arrayinbuf(const void* buf,size_t len,
const void* arraystart,
size_t elements,size_t membersize);
int range_strinbuf(const void* buf,size_t len,const void* string);
int range_str2inbuf(const void* buf,size_t len,const void* string);
int range_str4inbuf(const void* buf,size_t len,const void* string);
DESCRIPTION
rangecheck.h provides several routines for range checking pointers. These routines are meant for code that has to validate the syntax and
semantics of buffers coming in from untrusted sources (like a network connection or an input file).
RETURN VALUE
The routines all return 0 on error, or 1 if the pointers were in range.
SEE ALSO range_validbuf(3), range_ptrinbuf(3), range_bufinbuf(3), range_arrayinbuf(3), range_strinbuf(3), range_str2inbuf(3), range_str4inbuf(3)rangecheck(3)