filedes.c

一个简单的操作系统minix的核心代码

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
				src/fs/filedes.c	 	 
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

22200	/* This file contains the procedures that manipulate file descriptors.
22201	 *
22202	 * The entry points into this file are
22203	 *   get_fd:    look for free file descriptor and free filp slots
22204	 *   get_filp:  look up the filp entry for a given file descriptor
22205	 *   find_filp: find a filp slot that points to a given inode
22206	 */
22207	
22208	#include "fs.h"
22209	#include "file.h"
22210	#include "fproc.h"
22211	#include "inode.h"
22212	
22213	/*===========================================================================*
22214	 *                              get_fd                                       *
22215	 *===========================================================================*/
22216	PUBLIC int get_fd(start, bits, k, fpt)
22217	int start;                      /* start of search (used for F_DUPFD) */
22218	mode_t bits;                    /* mode of the file to be created (RWX bits) */
22219	int *k;                         /* place to return file descriptor */
22220	struct filp **fpt;              /* place to return filp slot */
22221	{
22222	/* Look for a free file descriptor and a free filp slot.  Fill in the mode word
22223	 * in the latter, but don't claim either one yet, since the open() or creat()
22224	 * may yet fail.
22225	 */
22226	
22227	  register struct filp *f;
22228	  register int i;
22229	
22230	  *k = -1;                      /* we need a way to tell if file desc found */
22231	
22232	  /* Search the fproc fp_filp table for a free file descriptor. */
22233	  for (i = start; i < OPEN_MAX; i++) {
22234	        if (fp->fp_filp[i] == NIL_FILP) {
22235	                /* A file descriptor has been located. */
22236	                *k = i;
22237	                break;
22238	        }
22239	  }
22240	
22241	  /* Check to see if a file descriptor has been found. */
22242	  if (*k < 0) return(EMFILE);   /* this is why we initialized k to -1 */
22243	
22244	  /* Now that a file descriptor has been found, look for a free filp slot. */
22245	  for (f = &filp[0]; f < &filp[NR_FILPS]; f++) {
22246	        if (f->filp_count == 0) {
22247	                f->filp_mode = bits;
22248	                f->filp_pos = 0L;
22249	                f->filp_flags = 0;
22250	                *fpt = f;
22251	                return(OK);
22252	        }
22253	  }
22254	
22255	  /* If control passes here, the filp table must be full.  Report that back. */
22256	  return(ENFILE);
22257	}
	
	
22260	/*===========================================================================*
22261	 *                              get_filp                                     *
22262	 *===========================================================================*/
22263	PUBLIC struct filp *get_filp(fild)
22264	int fild;                       /* file descriptor */
22265	{
22266	/* See if 'fild' refers to a valid file descr.  If so, return its filp ptr. */
22267	
22268	  err_code = EBADF;
22269	  if (fild < 0 || fild >= OPEN_MAX ) return(NIL_FILP);
22270	  return(fp->fp_filp[fild]);    /* may also be NIL_FILP */
22271	}
	
	
22274	/*===========================================================================*
22275	 *                              find_filp                                    *
22276	 *===========================================================================*/
22277	PUBLIC struct filp *find_filp(rip, bits)
22278	register struct inode *rip;     /* inode referred to by the filp to be found */
22279	Mode_t bits;                    /* mode of the filp to be found (RWX bits) */
22280	{
22281	/* Find a filp slot that refers to the inode 'rip' in a way as described
22282	 * by the mode bit 'bits'. Used for determining whether somebody is still
22283	 * interested in either end of a pipe.  Also used when opening a FIFO to
22284	 * find partners to share a filp field with (to shared the file position).
22285	 * Like 'get_fd' it performs its job by linear search through the filp table.
22286	 */
22287	
22288	  register struct filp *f;
22289	
22290	  for (f = &filp[0]; f < &filp[NR_FILPS]; f++) {
22291	        if (f->filp_count != 0 && f->filp_ino == rip && (f->filp_mode & bits)){
22292	                return(f);
22293	        }
22294	  }
22295	
22296	  /* If control passes here, the filp wasn't there.  Report that back. */
22297	  return(NIL_FILP);
22298	}