hos/kernel/fs/vfs.c

// vfs.c
// Author: Josh Holtrop
// Date: 08/22/04
// Modified: 12/21/04

#include "hos_defines.h"
#include "kout.h"
#include "fs/vfs.h"
#include "fs/ext2.h"
#include "kernel.h"
#include "mm/vmm.h"
#include "lang/asmfuncs.h"

vfs_fs_t *fses[VFS_MAX_FS];			// a vfs_fs structure for every filesystem we support
vfs_node_t *vfsMountTree;			// points to the root node ('/') of the VFS Mount Tree

// basic initialization routine, init all filesystem drivers
int	vfs_init()
{
	k_check(ext2_init(FS_EXT2), "ext2_init() failed!");
	return 0;
}

// called by a filesystem driver to let us know that it is ready to handle fs requests
int	vfs_register_fs(int fsn, vfs_fs_t *fs)
{
	if (fsn < 0 || fsn >= VFS_MAX_FS || fses[fsn])
	{
		kprintf("Invalid filesystem register: %d\n", fsn);
		return -1;
	}
	fses[fsn] = fs;
	return 0;
}

// called to mount a block device with a certain filesystem to a part of our VFS Mount Tree
int	vfs_mount(major_t maj, minor_t min, int fsType, char *mountPoint)
{
	if (mountPoint[0] != '/')
		return -1;				// mount point must be absolute
	int l = strlen(mountPoint);
	if (l < 1)
		return -7;				// mount point must be non-null string
	if (mountPoint[l-1] != '/')
		return -8;				// mount point must end with a '/' character
	if (fsType < 0 || fsType >= VFS_MAX_FS || !fses[fsType])
		return -2;				// invalid filesystem type
	if (vfs_find_mount(mountPoint))
		return -5;				// mount point already mounted
	void *super = fses[fsType]->mount_super(maj, min);
	if (!super)
		return -6;				// filesystem superblock not correctly identified
	vfs_mount_t *mnt = New(vfs_mount_t);
	if (!mnt)
		return -3;				// could not allocate memory
	mnt->refs = 0;
	mnt->major = maj;
	mnt->minor = min;
	mnt->super = super;
	if (vfs_add_mount(mnt, mountPoint))
	{
		kfree(mnt);
		return -4;				// could not add mount
	}
	return 0;
}

// invoked by vfs_mount to do the "dirty work" of adding the nodes to the tree
int	vfs_add_mount(vfs_mount_t *mnt, char *mountPoint)
{
	vfs_node_t *node = vfsMountTree;
	char *mp = mountPoint;
	if (!vfsMountTree)
	{
		vfsMountTree = New(vfs_node_t);
		node = vfsMountTree;
		node->chr = *mp;
		node->up = NULL;
		node->next = NULL;
		node->down = NULL;
		node->mount = NULL;
	}
	for (;;)
	{
		if (node->chr == *mp)				// got a match
		{
			mp++;
			if (*mp == 0)
			{
				if (node->mount)
					return -1;		// mount point already taken
				node->mount = mnt;
				return 0;
			}
			if (node->down)
				node = node->down;
			else
			{
				node->down = New(vfs_node_t);
				node->down->up = node;
				node = node->down;
				node->next = NULL;
				node->down = NULL;
				node->mount = NULL;
				node->chr = *mp;
			}
		}
		else if (node->next)
		{
			node = node->next;
		}
		else						// add a node for this character
		{
			node->next = New(vfs_node_t);
			node->next->up = node->up;
			node = node->next;
			node->next = NULL;
			node->down = NULL;
			node->mount = NULL;
			node->chr = *mp;
		}
	}	
}

// lookup a path and return the match structure for the deepest path matched
vfs_mount_match_t vfs_get_rel_path(char *path)
{
	vfs_mount_match_t matched = {NULL, 0};
	char *pp = path;
	int length = 0;
	vfs_node_t *node = vfsMountTree;
	while (*pp)
	{
		if (!node)
			break;
		if (node->chr == *pp)			// got a character match
		{
			length++;
			if (node->mount)		// and there is something mounted here
			{
				matched.mount = node->mount;
				matched.length = length;
			}
			pp++;
			node = node->down;
		}
		else
			node = node->next;
	}
	return matched;
}

// is mountPoint a valid mount point?
// returns a pointer to the mount structure if so
vfs_mount_t *vfs_find_mount(char *mountPoint)
{
	char *mp = mountPoint;
	vfs_node_t *node = vfsMountTree;
	while (node)
	{
		if (node->chr == *mp)
		{
			mp++;
			if (*mp == 0)			// we matched the whole mount point string
				return node->mount;
			node = node->down;
		}
		else
			node = node->next;
	}
	return NULL;
}

// unmount the mountPoint, remove nodes from tree that aren't used anymore
int	vfs_umount(char *mountPoint)
{
	char *mp = mountPoint;
	vfs_node_t *node = vfsMountTree;
	while (node)
	{
		if (node->chr == *mp)
		{
			mp++;
			if (*mp == 0)			// we matched the whole mount point string
			{
				// is there something mounted underneath this directory?
				if (node->down)
					return -3;	// yes, don't umount
				kfree(node->mount);
				node->mount = NULL;
				return vfs_retire_node(node);
			}
			node = node->down;
		}
		else
			node = node->next;
	}
	return -2;					// mount point does not exist
}

// remove this node from the tree if it is not needed anymore
int	vfs_retire_node(vfs_node_t *node)
{
	if (node->down)
		return 0;				// node is part of another mount point, don't remove
	if (node->mount)
		return 0;				// something is still mounted here
	if (!node->up)
	{
		kfree(node);
		vfsMountTree = NULL;
		return 0;				// we unmounted the root directory
	}
	// 3 cases left: node is first child (or only child), middle child, or last child
	if (node->up->down == node)			// first child
	{
		node->up->down = node->next;		// re-point parent to next child
		int r = vfs_retire_node(node->up);	// retire parent if we were an only-child
		kfree(node);
		return r;
	}
	vfs_node_t *onode = node->up->down;		// onode points to first child
	while (onode)
	{
		if (onode->next == node)		// onode is child before node
		{
			onode->next = node->next;
			kfree(node);
			return 0;
		}
		onode = onode->next;
	}
	return -1;					// node wasn't found following onode
}


// debug routine to draw the VFS Mount Tree
void	vfs_dump_tree()
{
	if (!vfsMountTree)
		kprintf("vfsMountTree == NULL!\n");
	else
		vfs_dump_node(vfsMountTree, 0);
}

void	vfs_dump_node(vfs_node_t *node, int level)
{
	int i;
	for (i = 0; i < level; i++)
	{
		putc(' ');
	}
	kprintf("%c (0x%x) mount: 0x%x, up: 0x%x, next:0x%x, down:0x%x\n", node->chr, node, node->mount, node->up, node->next, node->down);
	node = node->down;
	if (!node)
		return;
	while (node)
	{
		vfs_dump_node(node, level + 1);
		node = node->next;
	}
}