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Subject[PATCH] lazy umount (2/4)
Part 2/4:
Added minimal rootfs (read-only root directory - absolute minimum,
just to have something to go with root vfsmount), Now we have a fixed
root vfsmount and that allows to kill a lot of special-casing,

diff -urN S10-pre9-move_vfsmnt/fs/super.c S10-pre9-root_vfsmnt/fs/super.c
--- S10-pre9-move_vfsmnt/fs/super.c Fri Sep 14 14:02:32 2001
+++ S10-pre9-root_vfsmnt/fs/super.c Fri Sep 14 14:03:34 2001
@@ -280,6 +280,7 @@
}

static LIST_HEAD(vfsmntlist);
+static struct vfsmount *root_vfsmnt;

static struct list_head *mount_hashtable;
static int hash_mask, hash_bits;
@@ -346,52 +347,6 @@
nd->dentry->d_mounted++;
}

-/**
- * add_vfsmnt - add a new mount node
- * @nd: location of mountpoint or %NULL if we want a root node
- * @root: root of (sub)tree to be mounted
- * @dev_name: device name to show in /proc/mounts or %NULL (for "none").
- *
- * This is VFS idea of mount. New node is allocated, bound to a tree
- * we are mounting and optionally (OK, usually) registered as mounted
- * on a given mountpoint. Returns a pointer to new node or %NULL in
- * case of failure.
- *
- * Potential reason for failure (aside of trivial lack of memory) is a
- * deleted mountpoint. Caller must hold ->i_zombie on mountpoint
- * dentry (if any).
- */
-
-static struct vfsmount *add_vfsmnt(struct dentry *root, const char *dev_name)
-{
- struct vfsmount *mnt;
- struct super_block *sb = root->d_inode->i_sb;
- char *name;
-
- mnt = alloc_vfsmnt();
- if (!mnt)
- goto out;
-
- /* It may be NULL, but who cares? */
- if (dev_name) {
- name = kmalloc(strlen(dev_name)+1, GFP_KERNEL);
- if (name) {
- strcpy(name, dev_name);
- mnt->mnt_devname = name;
- }
- }
- mnt->mnt_sb = sb;
- mnt->mnt_root = dget(root);
- mnt->mnt_mountpoint = mnt->mnt_root;
- mnt->mnt_parent = mnt;
-
- spin_lock(&dcache_lock);
- list_add(&mnt->mnt_list, vfsmntlist.prev);
- spin_unlock(&dcache_lock);
-out:
- return mnt;
-}
-
static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root)
{
char *name = old->mnt_devname;
@@ -1200,8 +1155,7 @@
list_del(&mnt->mnt_list);
spin_unlock(&dcache_lock);
mntput(mnt);
- if (parent_nd.mnt != mnt)
- path_release(&parent_nd);
+ path_release(&parent_nd);
return 0;
}
spin_unlock(&dcache_lock);
@@ -1241,8 +1195,7 @@
list_del(&mnt->mnt_list);
spin_unlock(&dcache_lock);
mntput(mnt);
- if (parent_nd.mnt != mnt)
- path_release(&parent_nd);
+ path_release(&parent_nd);
return 0;
}

@@ -1601,6 +1554,7 @@

void __init mount_root(void)
{
+ struct nameidata root_nd;
struct file_system_type * fs_type;
struct super_block * sb;
struct vfsmount *vfsmnt;
@@ -1610,6 +1564,7 @@
void *handle;
char path[64];
int path_start = -1;
+ char *name = "/dev/root";

#ifdef CONFIG_ROOT_NFS
void *data;
@@ -1746,13 +1701,26 @@
fs_type->name,
(sb->s_flags & MS_RDONLY) ? " readonly" : "");
if (path_start >= 0) {
+ name = path + path_start;
devfs_mk_symlink (NULL, "root", DEVFS_FL_DEFAULT,
- path + 5 + path_start, NULL, NULL);
- memcpy (path + path_start, "/dev/", 5);
- vfsmnt = add_vfsmnt(sb->s_root, path + path_start);
+ name + 5, NULL, NULL);
+ memcpy (name, "/dev/", 5);
}
- else
- vfsmnt = add_vfsmnt(sb->s_root, "/dev/root");
+ vfsmnt = alloc_vfsmnt();
+ if (!vfsmnt)
+ panic("VFS: alloc_vfsmnt failed for root fs");
+
+ vfsmnt->mnt_devname = kmalloc(strlen(name)+1, GFP_KERNEL);
+ if (vfsmnt->mnt_devname)
+ strcpy(vfsmnt->mnt_devname, name);
+ vfsmnt->mnt_sb = sb;
+ vfsmnt->mnt_root = dget(sb->s_root);
+
+ root_nd.mnt = root_vfsmnt;
+ root_nd.dentry = root_vfsmnt->mnt_sb->s_root;
+ graft_tree(vfsmnt, &root_nd);
+ mntput(vfsmnt);
+
/* FIXME: if something will try to umount us right now... */
if (vfsmnt) {
set_fs_root(current->fs, vfsmnt, sb->s_root);
@@ -1761,10 +1729,8 @@
bdput(bdev); /* sb holds a reference */
return;
}
- panic("VFS: add_vfsmnt failed for root fs");
}

-
static void chroot_fs_refs(struct dentry *old_root,
struct vfsmount *old_rootmnt,
struct dentry *new_root,
@@ -1878,15 +1844,12 @@
detach_mnt(new_nd.mnt, &parent_nd);
detach_mnt(root_mnt, &root_parent);
attach_mnt(root_mnt, &old_nd);
- if (root_parent.mnt != root_mnt)
- attach_mnt(new_nd.mnt, &root_parent);
+ attach_mnt(new_nd.mnt, &root_parent);
spin_unlock(&dcache_lock);
chroot_fs_refs(root,root_mnt,new_nd.dentry,new_nd.mnt);
error = 0;
- if (root_parent.mnt != root_mnt)
- path_release(&root_parent);
- if (parent_nd.mnt != new_nd.mnt)
- path_release(&parent_nd);
+ path_release(&root_parent);
+ path_release(&parent_nd);
out2:
up(&old_nd.dentry->d_inode->i_zombie);
up(&mount_sem);
@@ -1959,24 +1922,19 @@
if (!blivet) {
spin_lock(&dcache_lock);
list_del(&old_rootmnt->mnt_list);
- if (atomic_read(&old_rootmnt->mnt_count) > 2) {
- spin_unlock(&dcache_lock);
- mntput(old_rootmnt);
- blivet = -EBUSY;
- } else {
- spin_unlock(&dcache_lock);
- mntput(old_rootmnt);
- if (parent_nd.mnt != old_rootmnt)
- path_release(&parent_nd);
- mntput(old_rootmnt);
- ioctl_by_bdev(ramdisk, BLKFLSBUF, 0);
- printk("okay\n");
- error = 0;
- }
+ spin_unlock(&dcache_lock);
+ mntput(old_rootmnt);
+ mntput(old_rootmnt);
+ blivet = ioctl_by_bdev(ramdisk, BLKFLSBUF, 0);
+ path_release(&parent_nd);
blkdev_put(ramdisk, BDEV_FS);
}
- if (blivet)
+ if (blivet) {
printk(KERN_ERR "error %d\n", blivet);
+ } else {
+ printk("okay\n");
+ error = 0;
+ }
kfree(new_devname);
return error;
}
@@ -1991,8 +1949,7 @@
spin_unlock(&dcache_lock);

/* put the old stuff */
- if (parent_nd.mnt != old_rootmnt)
- path_release(&parent_nd);
+ path_release(&parent_nd);
mntput(old_rootmnt);
path_release(&nd);
return 0;
@@ -2000,6 +1957,54 @@

#endif

+/*
+ * Absolutely minimal fake fs - only empty root directory and nothing else.
+ * In 2.5 we'll use ramfs or tmpfs, but for now it's all we need - just
+ * something to go with root vfsmount.
+ */
+static struct dentry *rootfs_lookup(struct inode *dir, struct dentry *dentry)
+{
+ d_add(dentry, NULL);
+ return NULL;
+}
+static struct file_operations rootfs_dir_operations = {
+ read: generic_read_dir,
+ readdir: dcache_readdir,
+};
+static struct inode_operations rootfs_dir_inode_operations = {
+ lookup: rootfs_lookup,
+};
+static struct super_block *rootfs_read_super(struct super_block * sb, void * data, int silent)
+{
+ struct inode * inode;
+ struct dentry * root;
+ static struct super_operations s_ops = {};
+ sb->s_op = &s_ops;
+ inode = new_inode(sb);
+ if (!inode)
+ return NULL;
+ inode->i_mode = S_IFDIR|0555;
+ inode->i_uid = inode->i_gid = 0;
+ inode->i_op = &rootfs_dir_inode_operations;
+ inode->i_fop = &rootfs_dir_operations;
+ root = d_alloc_root(inode);
+ if (!root) {
+ iput(inode);
+ return NULL;
+ }
+ sb->s_root = root;
+ return sb;
+}
+static DECLARE_FSTYPE(root_fs_type, "rootfs", rootfs_read_super, FS_NOMOUNT);
+
+static void __init init_mount_tree(void)
+{
+ register_filesystem(&root_fs_type);
+ root_vfsmnt = do_kern_mount("rootfs", 0, "rootfs", NULL);
+ if (IS_ERR(root_vfsmnt))
+ panic("can't allocate root vfsmount");
+}
+
void __init mnt_init(unsigned long mempages)
{
struct list_head *d;
@@ -2055,4 +2060,5 @@
d++;
i--;
} while (i);
+ init_mount_tree();
}

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