[PATCH] proc: Make the generation of the self symlink table driven

This patch generalizes the concept of files in /proc that are related to
processes but live in the root directory of /proc

Ideally this would reuse infrastructure from the rest of the process specific
parts of proc but unfortunately security_task_to_inode must not be called on
files that are not strictly per process.  security_task_to_inode really needs
to be reexamined as the security label can change in important places that we
are not currently catching, but I'm not certain that simplifies this problem.

By at least matching the structure of the rest of proc we get more idiom reuse
and it becomes easier to spot problems in the way things are put together.

Later things like /proc/mounts are likely to be moved into proc_base as well.
If union mounts are ever supported we may be able to make /proc a union mount,
and properly split it into 2 filesystems.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/proc/base.c

@@ -1673,6 +1673,108 @@ static struct inode_operations proc_self_inode_operations = {
 	.follow_link	= proc_self_follow_link,
 };
 
+/*
+ * proc base
+ *
+ * These are the directory entries in the root directory of /proc
+ * that properly belong to the /proc filesystem, as they describe
+ * describe something that is process related.
+ */
+static struct pid_entry proc_base_stuff[] = {
+	NOD(PROC_TGID_INO, 	"self", S_IFLNK|S_IRWXUGO,
+		&proc_self_inode_operations, NULL, {}),
+	{}
+};
+
+/*
+ *	Exceptional case: normally we are not allowed to unhash a busy
+ * directory. In this case, however, we can do it - no aliasing problems
+ * due to the way we treat inodes.
+ */
+static int proc_base_revalidate(struct dentry *dentry, struct nameidata *nd)
+{
+	struct inode *inode = dentry->d_inode;
+	struct task_struct *task = get_proc_task(inode);
+	if (task) {
+		put_task_struct(task);
+		return 1;
+	}
+	d_drop(dentry);
+	return 0;
+}
+
+static struct dentry_operations proc_base_dentry_operations =
+{
+	.d_revalidate	= proc_base_revalidate,
+	.d_delete	= pid_delete_dentry,
+};
+
+static struct dentry *proc_base_lookup(struct inode *dir, struct dentry *dentry)
+{
+	struct inode *inode;
+	struct dentry *error;
+	struct task_struct *task = get_proc_task(dir);
+	struct pid_entry *p;
+	struct proc_inode *ei;
+
+	error = ERR_PTR(-ENOENT);
+	inode = NULL;
+
+	if (!task)
+		goto out_no_task;
+
+	/* Lookup the directory entry */
+	for (p = proc_base_stuff; p->name; p++) {
+		if (p->len != dentry->d_name.len)
+			continue;
+		if (!memcmp(dentry->d_name.name, p->name, p->len))
+			break;
+	}
+	if (!p->name)
+		goto out;
+
+	/* Allocate the inode */
+	error = ERR_PTR(-ENOMEM);
+	inode = new_inode(dir->i_sb);
+	if (!inode)
+		goto out;
+
+	/* Initialize the inode */
+	ei = PROC_I(inode);
+	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
+	inode->i_ino = fake_ino(0, p->type);
+
+	/*
+	 * grab the reference to the task.
+	 */
+	ei->pid = get_pid(task_pid(task));
+	if (!ei->pid)
+		goto out_iput;
+
+	inode->i_uid = 0;
+	inode->i_gid = 0;
+	inode->i_mode = p->mode;
+	if (S_ISDIR(inode->i_mode))
+		inode->i_nlink = 2;
+	if (S_ISLNK(inode->i_mode))
+		inode->i_size = 64;
+	if (p->iop)
+		inode->i_op = p->iop;
+	if (p->fop)
+		inode->i_fop = p->fop;
+	ei->op = p->op;
+	dentry->d_op = &proc_base_dentry_operations;
+	d_add(dentry, inode);
+	error = NULL;
+out:
+	put_task_struct(task);
+out_no_task:
+	return error;
+out_iput:
+	iput(inode);
+	goto out;
+}
+
 /*
  * Thread groups
  */
@@ -1819,24 +1921,12 @@ struct dentry *proc_pid_lookup(struct inode *dir, struct dentry * dentry, struct
 	struct dentry *result = ERR_PTR(-ENOENT);
 	struct task_struct *task;
 	struct inode *inode;
-	struct proc_inode *ei;
 	unsigned tgid;
 
-	if (dentry->d_name.len == 4 && !memcmp(dentry->d_name.name,"self",4)) {
-		inode = new_inode(dir->i_sb);
-		if (!inode)
-			return ERR_PTR(-ENOMEM);
-		ei = PROC_I(inode);
-		inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
-		inode->i_ino = fake_ino(0, PROC_TGID_INO);
-		ei->pde = NULL;
-		inode->i_mode = S_IFLNK|S_IRWXUGO;
-		inode->i_uid = inode->i_gid = 0;
-		inode->i_size = 64;
-		inode->i_op = &proc_self_inode_operations;
-		d_add(dentry, inode);
-		return NULL;
-	}
+	result = proc_base_lookup(dir, dentry);
+	if (!IS_ERR(result) || PTR_ERR(result) != -ENOENT)
+		goto out;
+
 	tgid = name_to_int(dentry);
 	if (tgid == ~0U)
 		goto out;
@@ -1922,12 +2012,11 @@ int proc_pid_readdir(struct file * filp, void * dirent, filldir_t filldir)
 	struct task_struct *task;
 	int tgid;
 
-	if (!nr) {
-		ino_t ino = fake_ino(0,PROC_TGID_INO);
-		if (filldir(dirent, "self", 4, filp->f_pos, ino, DT_LNK) < 0)
-			return 0;
-		filp->f_pos++;
-		nr++;
+	for (; nr < (ARRAY_SIZE(proc_base_stuff) - 1); filp->f_pos++, nr++) {
+		struct pid_entry *p = &proc_base_stuff[nr];
+		if (filldir(dirent, p->name, p->len, filp->f_pos,
+			    fake_ino(0, p->type), p->mode >> 12) < 0)
+			goto out;
 	}
 
 	tgid = filp->f_pos - TGID_OFFSET;