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Full Discussion: File Descriptor Table
Top Forums UNIX for Advanced & Expert Users File Descriptor Table Post 302148517 by Ashaman0 on Sunday 2nd of December 2007 08:37:57 PM
Old 12-02-2007
File Descriptor Table

Im working on writing a small operating system. I am currently working on implementing dup, dup2, pipe, and close and I need to implement some type of file descriptor table in my PCB.

I was wondering if there is anyone who is familiar with linux/unix implementation of these tables who could explain to me a little about how they are implemented. I know basically how it works, what I am really having a little trouble with now is how file descriptors are mapped to input/output streams. Are their pointers to the pipe / device, or is there some other way its done? Thanks.

-shane
 

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dup(2)								System Calls Manual							    dup(2)

NAME
dup - duplicate an open file descriptor SYNOPSIS
DESCRIPTION
fildes is a file descriptor obtained from a or system call. returns a new file descriptor having the following in common with the origi- nal: o Same open file (or pipe). o Same file pointer (i.e., both file descriptors share one file pointer). o Same access mode (read, write or read/write). o Same file status flags (see fcntl(2), The new file descriptor is set to remain open across system calls. See fcntl(2). The file descriptor returned is the lowest one available. RETURN VALUE
Upon successful completion, the file descriptor is returned as a non-negative integer. Otherwise, a value of -1 is returned and is set to indicate the error. ERRORS
fails if one or more of the following is true: fildes is not a valid open file descriptor. Request violates the maximum number of open file descriptors. AUTHOR
was developed by AT&T and HP. SEE ALSO
close(2), creat(2), dup2(2), exec(2), fcntl(2), open(2), pipe(2), privileges(5). STANDARDS CONFORMANCE
dup(2)
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