FILE(9) | Kernel Developer's Manual | FILE(9) |
file
, closef
,
ffree
, FILE_IS_USABLE
,
FILE_USE
, FILE_UNUSE
,
FILE_SET_MATURE
—
#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);
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 contains 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 operations. 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
themselves.
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 reference is created, the reference count is incremented. When a descriptor is closed, the reference 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) system 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 writing. The following flags and their corresponding open(2) flags are:
O_APPEND
O_ASYNC
O_SYNC
O_NONBLOCK
O_NONBLOCK
O_NONBLOCK
O_SYNC
O_DSYNC
O_RSYNC
O_ALT_IO
Some additional state-specific flags are recorded in the f_iflags member. Valid values include:
FIF_WANTCLOSE
FIF_LARVAL
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.
closef
(fp,
l)closef
() function
release all locks on the file owned by lwp l,
decrements the reference count on the file entry, and invokes
ffree
() to free the file entry.ffree
(struct file *fp)FILE_IS_USABLE
(fp)FIF_WANTCLOSE
flag nor the
FIF_LARVAL
flag is set in
f_iflags.FILE_USE
(fp)FILE_UNUSE
(fp,
l)FIF_WANTCLOSE
flag is set in
f_iflags, the file entry is freed.FILE_SET_MATURE
(fp)FIF_LARVAL
flag in
f_iflags.May 17, 2009 | NetBSD 9.0 |