minix/servers/fs/filedes.c

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2005-04-21 16:53:53 +02:00
/* This file contains the procedures that manipulate file descriptors.
*
* The entry points into this file are
* get_fd: look for free file descriptor and free filp slots
* get_filp: look up the filp entry for a given file descriptor
* find_filp: find a filp slot that points to a given inode
*/
#include "fs.h"
#include "file.h"
#include "fproc.h"
#include "inode.h"
/*===========================================================================*
* get_fd *
*===========================================================================*/
PUBLIC int get_fd(int start, mode_t bits, int *k, struct filp **fpt)
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{
/* Look for a free file descriptor and a free filp slot. Fill in the mode word
* in the latter, but don't claim either one yet, since the open() or creat()
* may yet fail.
*/
register struct filp *f;
register int i;
*k = -1; /* we need a way to tell if file desc found */
/* Search the fproc fp_filp table for a free file descriptor. */
for (i = start; i < OPEN_MAX; i++) {
if (fp->fp_filp[i] == NIL_FILP) {
/* A file descriptor has been located. */
*k = i;
break;
}
}
/* Check to see if a file descriptor has been found. */
if (*k < 0) return(EMFILE); /* this is why we initialized k to -1 */
/* Now that a file descriptor has been found, look for a free filp slot. */
for (f = &filp[0]; f < &filp[NR_FILPS]; f++) {
if (f->filp_count == 0) {
f->filp_mode = bits;
f->filp_pos = 0L;
f->filp_selectors = 0;
f->filp_select_ops = 0;
f->filp_pipe_select_ops = 0;
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f->filp_flags = 0;
*fpt = f;
return(OK);
}
}
/* If control passes here, the filp table must be full. Report that back. */
return(ENFILE);
}
/*===========================================================================*
* get_filp *
*===========================================================================*/
PUBLIC struct filp *get_filp(fild)
int fild; /* file descriptor */
{
/* See if 'fild' refers to a valid file descr. If so, return its filp ptr. */
err_code = EBADF;
if (fild < 0 || fild >= OPEN_MAX ) return(NIL_FILP);
return(fp->fp_filp[fild]); /* may also be NIL_FILP */
}
/*===========================================================================*
* find_filp *
*===========================================================================*/
PUBLIC struct filp *find_filp(register struct inode *rip, mode_t bits)
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{
/* Find a filp slot that refers to the inode 'rip' in a way as described
* by the mode bit 'bits'. Used for determining whether somebody is still
* interested in either end of a pipe. Also used when opening a FIFO to
* find partners to share a filp field with (to shared the file position).
* Like 'get_fd' it performs its job by linear search through the filp table.
*/
register struct filp *f;
for (f = &filp[0]; f < &filp[NR_FILPS]; f++) {
if (f->filp_count != 0 && f->filp_ino == rip && (f->filp_mode & bits)){
return(f);
}
}
/* If control passes here, the filp wasn't there. Report that back. */
return(NIL_FILP);
}