Copyright (c) 1990 The Regents of the University of California.
All rights reserved.

%sccs.include.redist.man%

@(#)A.t 5.1 (Berkeley) 04/16/91

.bp .nr PS 10 .nr VS 12 Appendix A - Implementation Details

.vS
/*
 * This structure defines the control data for the memory
 * based file system.
 */
struct mfsnode {
 struct vnode *mfs_vnode; /* vnode associated with this mfsnode */
 caddr_t mfs_baseoff; /* base of file system in memory */
 long mfs_size; /* size of memory file system */
 pid_t mfs_pid; /* supporting process pid */
 struct buf *mfs_buflist; /* list of I/O requests */
};

/*
 * Convert between mfsnode pointers and vnode pointers
 */
#define VTOMFS(vp) ((struct mfsnode *)(vp)->v_data)
#define MFSTOV(mfsp) ((mfsp)->mfs_vnode)
#define MFS_EXIT (struct buf *)-1

/*
 * Arguments to mount MFS
 */
struct mfs_args {
 char *name; /* name to export for statfs */
 caddr_t base; /* base address of file system in memory */
 u_long size; /* size of file system */
};
.bp
/*
 * Mount an MFS filesystem.
 */
mfs_mount(mp, path, data)
 struct mount *mp;
 char *path;
 caddr_t data;
{
 struct vnode *devvp;
 struct mfsnode *mfsp;
 struct buf *bp;
 struct mfs_args args;

 /*
 * Create a block device to represent the disk.
 */
 devvp = getnewvnode(VT_MFS, VBLK, &mfs_vnodeops);
 mfsp = VTOMFS(devvp);
 /*
 * Save base address of the filesystem from the supporting process.
 */
 copyin(data, &args, (sizeof mfs_args));
 mfsp->mfs_baseoff = args.base;
 mfsp->mfs_size = args.size;
 /*
 * Record the process identifier of the supporting process.
 */
 mfsp->mfs_pid = u.u_procp->p_pid;
 /*
 * Mount the filesystem.
 */
 mfsp->mfs_buflist = NULL;
 mountfs(devvp, mp);
 /*
 * Loop processing I/O requests.
 */
 while (mfsp->mfs_buflist != MFS_EXIT) {
 while (mfsp->mfs_buflist != NULL) {
 bp = mfsp->mfs_buflist;
 mfsp->mfs_buflist = bp->av_forw;
 offset = mfsp->mfs_baseoff + (bp->b_blkno * DEV_BSIZE);
 if (bp->b_flags & B_READ)
 copyin(offset, bp->b_un.b_addr, bp->b_bcount);
 else /* write_request */
 copyout(bp->b_un.b_addr, offset, bp->b_bcount);
 biodone(bp);
 }
 sleep((caddr_t)devvp, PWAIT);
 }
}
.bp
/*
 * If the MFS process requests the I/O then we must do it directly.
 * Otherwise put the request on the list and request the MFS process
 * to be run.
 */
mfs_strategy(bp)
 struct buf *bp;
{
 struct vnode *devvp;
 struct mfsnode *mfsp;
 off_t offset;

 devvp = bp->b_vp;
 mfsp = VTOMFS(devvp);
 if (mfsp->mfs_pid == u.u_procp->p_pid) {
 offset = mfsp->mfs_baseoff + (bp->b_blkno * DEV_BSIZE);
 if (bp->b_flags & B_READ)
 copyin(offset, bp->b_un.b_addr, bp->b_bcount);
 else /* write_request */
 copyout(bp->b_un.b_addr, offset, bp->b_bcount);
 biodone(bp);
 } else {
 bp->av_forw = mfsp->mfs_buflist;
 mfsp->mfs_buflist = bp;
 wakeup((caddr_t)bp->b_vp);
 }
}

/*
 * The close routine is called by unmount after the filesystem
 * has been successfully unmounted.
 */
mfs_close(devvp)
 struct vnode *devvp;
{
 struct mfsnode *mfsp = VTOMFS(vp);
 struct buf *bp;

 /*
 * Finish any pending I/O requests.
 */
 while (bp = mfsp->mfs_buflist) {
 mfsp->mfs_buflist = bp->av_forw;
 mfs_doio(bp, mfsp->mfs_baseoff);
 wakeup((caddr_t)bp);
 }
 /*
 * Send a request to the filesystem server to exit.
 */
 mfsp->mfs_buflist = MFS_EXIT;
 wakeup((caddr_t)vp);
}
.vE