fsinterface.ms

早期freebsd实现

 */
enum vtype 	{ VNON, VREG, VDIR, VBLK, VCHR, VLNK, VSOCK };

struct vnode {
	u_short	v_flag;			/* vnode flags (see below) */
	u_short	v_count;		/* reference count */
	u_short	v_shlockc;		/* count of shared locks */
	u_short	v_exlockc;		/* count of exclusive locks */
	struct vfs	*v_vfsmountedhere;	/* ptr to vfs mounted here */
	struct vfs	*v_vfsp;		/* ptr to vfs we are in */
	struct vnodeops	*v_op;			/* vnode operations */
\fB+\fP	struct text	*v_text;		/* text/mapped region */
	enum vtype	v_type;			/* vnode type */
	caddr_t	v_data;			/* private data for fs */
};
.DE
.DS
.ta \w'#define\0\0'u +\w'NOFOLLOW\0\0'u +\w'0x40\0\0\0\0\0\0\0'u
/*
 * vnode flags.
 */
#define	VROOT	0x01	/* root of its file system */
#define	VTEXT	0x02	/* vnode is a pure text prototype */
#define	VEXLOCK	0x10	/* exclusive lock */
#define	VSHLOCK	0x20	/* shared lock */
#define	VLWAIT	0x40	/* proc is waiting on shared or excl. lock */
.DE
.LP
The operations supported by the filesystems on individual \fIvnode\fP\^s
are:
.DS
.ta .5i +\w'int\0\0\0\0\0'u  +\w'(*vn_getattr)(\0\0\0\0\0'u
/*
 * Operations on vnodes.
 */
struct vnodeops {
\fB!\fP	int	(*vn_lookup)(		/* ndp */ );
\fB!\fP	int	(*vn_create)(		/* ndp, vap, fflags */ );
\fB+\fP	int	(*vn_mknod)(		/* ndp, vap, fflags */ );
\fB!\fP	int	(*vn_open)(		/* vp, fflags, cred */ );
	int	(*vn_close)(		/* vp, fflags, cred */ );
	int	(*vn_access)(		/* vp, fflags, cred */ );
	int	(*vn_getattr)(		/* vp, vap, cred */ );
	int	(*vn_setattr)(		/* vp, vap, cred */ );

\fB+\fP	int	(*vn_read)(		/* vp, uiop, offp, ioflag, cred */ );
\fB+\fP	int	(*vn_write)(		/* vp, uiop, offp, ioflag, cred */ );
\fB!\fP	int	(*vn_ioctl)(		/* vp, com, data, fflag, cred */ );
	int	(*vn_select)(		/* vp, which, cred */ );
\fB+\fP	int	(*vn_mmap)(		/* vp, ..., cred */ );
	int	(*vn_fsync)(		/* vp, cred */ );
\fB+\fP	int	(*vn_seek)(		/* vp, offp, off, whence */ );

\fB!\fP	int	(*vn_remove)(		/* ndp */ );
\fB!\fP	int	(*vn_link)(		/* vp, ndp */ );
\fB!\fP	int	(*vn_rename)(		/* src ndp, target ndp */ );
\fB!\fP	int	(*vn_mkdir)(		/* ndp, vap */ );
\fB!\fP	int	(*vn_rmdir)(		/* ndp */ );
\fB!\fP	int	(*vn_symlink)(		/* ndp, vap, nm */ );
	int	(*vn_readdir)(		/* vp, uiop, offp, ioflag, cred */ );
	int	(*vn_readlink)(		/* vp, uiop, ioflag, cred */ );

\fB+\fP	int	(*vn_abortop)(		/* ndp */ );
\fB+\fP	int	(*vn_lock)(		/* vp */ );
\fB+\fP	int	(*vn_unlock)(		/* vp */ );
\fB!\fP	int	(*vn_inactive)(		/* vp */ );
};
.DE
.DS
.ta \w'#define\0\0'u +\w'NOFOLLOW\0\0'u +\w'0x40\0\0\0\0\0'u
/*
 * flags for ioflag
 */
#define	IO_UNIT	0x01		/* do io as atomic unit for VOP_RDWR */
#define	IO_APPEND	0x02		/* append write for VOP_RDWR */
#define	IO_SYNC	0x04		/* sync io for VOP_RDWR */
.DE
.LP
The argument types listed in the comments following each operation are:
.sp
.IP ndp 10
A pointer to a \fInameidata\fP structure.
.IP vap
A pointer to a \fIvattr\fP structure (vnode attributes; see below).
.IP fflags
File open flags, possibly including O_APPEND, O_CREAT, O_TRUNC and O_EXCL.
.IP vp
A pointer to a \fIvnode\fP previously obtained with \fIvn_lookup\fP.
.IP cred
A pointer to a \fIucred\fP credentials structure.
.IP uiop
A pointer to a \fIuio\fP structure.
.IP ioflag
Any of the IO flags defined above.
.IP com
An \fIioctl\fP command, with type \fIunsigned long\fP.
.IP data
A pointer to a character buffer used to pass data to or from an \fIioctl\fP.
.IP which
One of FREAD, FWRITE or 0 (select for exceptional conditions).
.IP off
A file offset of type \fIoff_t\fP.
.IP offp
A pointer to file offset of type \fIoff_t\fP.
.IP whence
One of L_SET, L_INCR, or L_XTND.
.IP fhp
A pointer to a file handle buffer.
.sp
.PP
Several changes have been made to Sun's set of vnode operations.
Most obviously, the \fIvn_lookup\fP receives a \fInameidata\fP structure
containing its arguments and context as described.
The same structure is also passed to one of the creation or deletion
entries if the lookup operation is for CREATE or DELETE to complete
an operation, or to the \fIvn_abortop\fP entry if no operation
is undertaken.
For filesystems that perform no locking between lookup for creation
or deletion and the call to implement that action,
the final pathname component may be left untranslated by the lookup
routine.
In any case, the pathname pointer points at the final name component,
and the \fInameidata\fP contains a reference to the vnode of the parent
directory.
The interface is thus flexible enough to accommodate filesystems
that are fully stateful or fully stateless, while avoiding redundant
operations whenever possible.
One operation remains problematical, the \fIvn_rename\fP call.
It is tempting to look up the source of the rename for deletion
and the target for creation.
However, filesystems that lock directories during such lookups must avoid
deadlock if the two paths cross.
For that reason, the source is translated for LOOKUP only,
with the WANTPARENT flag set;
the target is then translated with an operation of CREATE.
.PP
In addition to the changes concerned with the \fInameidata\fP interface,
several other changes were made in the vnode operations.
The \fIvn_rdrw\fP entry was split into \fIvn_read\fP and \fIvn_write\fP;
frequently, the read/write entry amounts to a routine that checks
the direction flag, then calls either a read routine or a write routine.
The two entries may be identical for any given filesystem;
the direction flag is contained in the \fIuio\fP given as an argument.
.PP
All of the read and write operations use a \fIuio\fP to describe
the file offset and buffer locations.
All of these fields must be updated before return.
In particular, the \fIvn_readdir\fP entry uses this
to return a new file offset token for its current location.
.PP
Several new operations have been added.
The first, \fIvn_seek\fP, is a concession to record-oriented files
such as directories.
It allows the filesystem to verify that a seek leaves a file at a sensible
offset, or to return a new offset token relative to an earlier one.
For most filesystems and files, this operation amounts to performing
simple arithmetic.
Another new entry point is \fIvn_mmap\fP, for use in mapping device memory
into a user process address space.
Its semantics are not yet decided.
The final additions are the \fIvn_lock\fP and \fIvn_unlock\fP entries.
These are used to request that the underlying file be locked against
changes for short periods of time if the filesystem implementation allows it.
They are used to maintain consistency
during internal operations such as \fIexec\fP,
and may not be used to construct atomic operations from other filesystem
operations.
.PP
The attributes of a vnode are not stored in the vnode,
as they might change with time and may need to be read from a remote
source.
Attributes have the form:
.DS
.ta .5i +\w'struct vnodeops\0\0'u +\w'*v_vfsmountedhere;\0\0\0'u
/*
 * Vnode attributes.  A field value of -1
 * represents a field whose value is unavailable
 * (getattr) or which is not to be changed (setattr).
 */
struct vattr {
	enum vtype	va_type;	/* vnode type (for create) */
	u_short	va_mode;	/* files access mode and type */
\fB!\fP	uid_t	va_uid;		/* owner user id */
\fB!\fP	gid_t	va_gid;		/* owner group id */
	long	va_fsid;	/* file system id (dev for now) */
\fB!\fP	long	va_fileid;	/* file id */
	short	va_nlink;	/* number of references to file */
	u_long	va_size;	/* file size in bytes (quad?) */
\fB+\fP	u_long	va_size1;	/* reserved if not quad */
	long	va_blocksize;	/* blocksize preferred for i/o */
	struct timeval	va_atime;	/* time of last access */
	struct timeval	va_mtime;	/* time of last modification */
	struct timeval	va_ctime;	/* time file changed */
	dev_t	va_rdev;	/* device the file represents */
	u_long	va_bytes;	/* bytes of disk space held by file */
\fB+\fP	u_long	va_bytes1;	/* reserved if va_bytes not a quad */
};
.DE
.SH
Conclusions
.PP
The Sun VFS filesystem interface is the most widely used generic
filesystem interface.
Of the interfaces examined, it creates the cleanest separation
between the filesystem-independent and -dependent layers and data structures.
It has several flaws, but it is felt that certain changes in the interface
can ameliorate most of them.
The interface proposed here includes those changes.
The proposed interface is now being implemented by the Computer Systems
Research Group at Berkeley.
If the design succeeds in improving the flexibility and performance
of the filesystem layering, it will be advanced as a model interface.
.SH
Acknowledgements
.PP
The filesystem interface described here is derived from Sun's VFS interface.
It also includes features similar to those of DEC's GFS interface.
We are indebted to members of the Sun and DEC system groups
for long discussions of the issues involved.
.br
.ne 2i
.SH
References

.IP Brownbridge82 \w'Satyanarayanan85\0\0'u
Brownbridge, D.R., L.F. Marshall, B. Randell,
``The Newcastle Connection, or UNIXes of the World Unite!,''
\fISoftware\- Practice and Experience\fP, Vol. 12, pp. 1147-1162, 1982.

.IP Cole85
Cole, C.T., P.B. Flinn, A.B. Atlas,
``An Implementation of an Extended File System for UNIX,''
\fIUsenix Conference Proceedings\fP,
pp. 131-150, June, 1985.

.IP Kleiman86
``Vnodes: An Architecture for Multiple File System Types in Sun UNIX,''
\fIUsenix Conference Proceedings\fP,
pp. 238-247, June, 1986.

.IP Leffler84
Leffler, S., M.K. McKusick, M. Karels,
``Measuring and Improving the Performance of 4.2BSD,''
\fIUsenix Conference Proceedings\fP, pp. 237-252, June, 1984.

.IP McKusick84
McKusick, M.K., W.N. Joy, S.J. Leffler, R.S. Fabry,
``A Fast File System for UNIX,'' \fITransactions on Computer Systems\fP,
Vol. 2, pp. 181-197,
ACM, August, 1984.

.IP McKusick85
McKusick, M.K., M. Karels, S. Leffler,
``Performance Improvements and Functional Enhancements in 4.3BSD,''
\fIUsenix Conference Proceedings\fP, pp. 519-531, June, 1985.

.IP Rifkin86
Rifkin, A.P., M.P. Forbes, R.L. Hamilton, M. Sabrio, S. Shah, and K. Yueh,
``RFS Architectural Overview,'' \fIUsenix Conference Proceedings\fP,
pp. 248-259, June, 1986.

.IP Ritchie74
Ritchie, D.M. and K. Thompson, ``The Unix Time-Sharing System,''
\fICommunications of the ACM\fP, Vol. 17, pp. 365-375, July, 1974.

.IP Rodriguez86
Rodriguez, R., M. Koehler, R. Hyde,
``The Generic File System,'' \fIUsenix Conference Proceedings\fP,
pp. 260-269, June, 1986.

.IP Sandberg85
Sandberg, R., D. Goldberg, S. Kleiman, D. Walsh, B. Lyon,
``Design and Implementation of the Sun Network Filesystem,''
\fIUsenix Conference Proceedings\fP,
pp. 119-130, June, 1985.

.IP Satyanarayanan85
Satyanarayanan, M., \fIet al.\fP,
``The ITC Distributed File System: Principles and Design,''
\fIProc. 10th Symposium on Operating Systems Principles\fP, pp. 35-50,
ACM, December, 1985.

.IP Walker85
Walker, B.J. and S.H. Kiser, ``The LOCUS Distributed Filesystem,''
\fIThe LOCUS Distributed System Architecture\fP,
G.J. Popek and B.J. Walker, ed., The MIT Press, Cambridge, MA, 1985.

.IP Weinberger84
Weinberger, P.J., ``The Version 8 Network File System,''
\fIUsenix Conference presentation\fP,
June, 1984.