usr/src/share/doc/papers/memfs/A.t

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.\"     @(#)A.t 5.1 (Berkeley) 4/16/91
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.bp
.nr PS 10
.nr VS 12
.SH
Appendix A - Implementation Details
.LP
.nf
.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