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NetBSD 6.1.5 - man page for ffree (netbsd section 9)

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FILE(9) 			  BSD Kernel Developer's Manual 			  FILE(9)

NAME
     file, closef, ffree, FILE_IS_USABLE, FILE_USE, FILE_UNUSE, FILE_SET_MATURE -- operations on
     file entries

SYNOPSIS
     #include <sys/file.h>

     int
     closef(struct file *fp, struct lwp *l);

     void
     ffree(struct file *fp);

     int
     FILE_IS_USABLE(struct file *fp);

     void
     FILE_USE(struct file *fp);

     void
     FILE_UNUSE(struct file *fp, struct lwp *l);

     void
     FILE_SET_MATURE(struct file *fp);

DESCRIPTION
     The file descriptor table of a process references a file entry for each file used by the
     kernel.  See filedesc(9) for details of the file descriptor table.  Each file entry is given
     by:

     struct file {
	     LIST_ENTRY(file) f_list;	     /* list of active files */
	     int	     f_flag;
	     int	     f_iflags;	     /* internal flags */
	     int	     f_type;	     /* descriptor type */
	     u_int	     f_count;	     /* reference count */
	     u_int	     f_msgcount;     /* message queue references */
	     int	     f_usecount;     /* number active users */
	     kauth_cred_t    f_cred;	     /* creds associated with descriptor */
	     struct fileops {
		     int (*fo_read)(struct file *fp, off_t *offset,
			     struct uio *uio, kauth_cred_t cred, int flags);
		     int (*fo_write)(struct file *fp, off_t *offset,
			     struct uio *uio, kauth_cred_t cred, int flags);
		     int (*fo_ioctl)(struct file *fp, u_long com, void *data,
			     struct lwp *l);
		     int (*fo_fcntl)(struct file *fp, u_int com, void *data,
			     struct lwp *l);
		     int (*fo_poll)(struct file *fp, int events,
			     struct lwp *l);
		     int (*fo_stat)(struct file *fp, struct stat *sp,
			     struct lwp *l);
		     int (*fo_close)(struct file *fp, struct lwp *l);
	     } *f_ops;
	     off_t	     f_offset;
	     void	  *f_data;	   /* descriptor data */
     };

     NetBSD treats file entries in an object-oriented fashion after they are created.  Each entry
     specifies the object type, f_type, which can have the values DTYPE_VNODE, DTYPE_SOCKET,
     DTYPE_PIPE and DTYPE_MISC.  The file entry also has a pointer to a data structure, f_data,
     that contains information specific to the instance of the underlying object.  The data
     structure is opaque to the routines that manipulate the file entry.  Each entry also con-
     tains an array of function pointers, f_ops, that translate the generic operations on a file
     descriptor into the specific action associated with its type.  A reference to the data
     structure is passed as the first parameter to a function that implements a file operation.
     The operations that must be implemented for each descriptor type are read, write, ioctl,
     fcntl, poll, stat, and close.  See vnfileops(9) for an overview of the vnode file opera-
     tions.  All state associated with an instance of an object must be stored in that instance's
     data structure; the underlying objects are not permitted to manipulate the file entry them-
     selves.

     For data files, the file entry points to a vnode(9) structure.  Pipes and sockets do not
     have data blocks allocated on the disk and are handled by the special-device filesystem that
     calls appropriate drivers to handle I/O for them.	For pipes, the file entry points to a
     system block that is used during data transfer.  For sockets, the file entry points to a
     system block that is used in doing interprocess communications.

     The descriptor table of a process (and thus access to the objects to which the descriptors
     refer) is inherited from its parent, so several different processes may reference the same
     file entry.  Thus, each file entry has a reference count, f_count.  Each time a new refer-
     ence is created, the reference count is incremented.  When a descriptor is closed, the ref-
     erence count is decremented.  When the reference count drops to zero, the file entry is
     freed.

     Some file descriptor semantics can be altered through the flags argument to the open(2) sys-
     tem call.	These flags are recorded in f_flags member of the file entry.  For example, the
     flags record whether the descriptor is open for reading, writing, or both reading and writ-
     ing.  The following flags and their corresponding open(2) flags are:

	   FAPPEND    O_APPEND
	   FASYNC     O_ASYNC
	   O_FSYNC    O_SYNC
	   FNDELAY    O_NONBLOCK
	   O_NDELAY   O_NONBLOCK
	   FNONBLOCK  O_NONBLOCK
	   FFSYNC     O_SYNC
	   FDSYNC     O_DSYNC
	   FRSYNC     O_RSYNC
	   FALTIO     O_ALT_IO

     Some additional state-specific flags are recorded in the f_iflags member.	Valid values
     include:

	   FIF_WANTCLOSE  If set, then the reference count on the file is zero, but there were
			  multiple users of the file.  This can happen if a file descriptor table
			  is shared by multiple processes.  This flag notifies potential users
			  that the file is closing and will prevent them from adding additional
			  uses to the file.
	   FIF_LARVAL	  The file entry is not fully constructed (mature) and should not be
			  used.

     The read(2) and write(2) system calls do not take an offset in the file as an argument.
     Instead, each read or write updates the current file offset, f_offset in the file according
     to the number of bytes transferred.  Since more than one process may open the same file and
     each needs its own offset in the file, the offset cannot be stored in the per-object data
     structure.

FUNCTIONS
     closef(fp, l)
	      The internal form of close(2) which decrements the reference count on file entry
	      fp.  The closef() function  release all locks on the file owned by lwp l, decre-
	      ments the reference count on the file entry, and invokes ffree() to free the file
	      entry.

     ffree(struct file *fp)
	      Free file entry fp.  The file entry was created in falloc(9).

     FILE_IS_USABLE(fp)
	      Ensure that the file entry is useable by ensuring that neither the FIF_WANTCLOSE
	      and FIF_LARVAL flags are not set in f_iflags.

     FILE_USE(fp)
	      Increment the reference count on file entry fp.

     FILE_UNUSE(fp, l)
	      Decrement the reference count on file entry fp.  If the FIF_WANTCLOSE flag is set
	      in f_iflags, the file entry is freed.

     FILE_SET_MATURE(fp)
	      Mark the file entry as being fully constructed (mature) by clearing the FIF_LARVAL
	      flag in f_iflags.

CODE REFERENCES
     The framework for file entry handling is implemented within the file
     sys/kern/kern_descrip.c.

SEE ALSO
     dofileread(9), filedesc(9), vnfileops(9), vnode(9)

BSD					   May 17, 2009 				      BSD
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