procfs: Use the proc generic infrastructure for proc/self.

I had visions at one point of splitting proc into two filesystems.  If
that had happened proc/self being the the part of proc that actually deals
with pids would have been a nice cleanup.  As it is proc/self requires
a lot of unnecessary infrastructure for a single file.

The only user visible change is that a mounted /proc for a pid namespace
that is dead now shows a broken proc symlink, instead of being completely
invisible.  I don't think anyone will notice or care.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

1 files changed, 59 insertions, 0 deletions

diff --git a/fs/proc/self.c b/fs/proc/self.c
new file mode 100644
index 000000000000..aa5cc3bff140
--- /dev/null
+++ b/fs/proc/self.c
@@ -0,0 +1,59 @@
+#include <linux/proc_fs.h>
+#include <linux/sched.h>
+#include <linux/namei.h>
+
+/*
+ * /proc/self:
+ */
+static int proc_self_readlink(struct dentry *dentry, char __user *buffer,
+                              int buflen)
+{
+        struct pid_namespace *ns = dentry->d_sb->s_fs_info;
+        pid_t tgid = task_tgid_nr_ns(current, ns);
+        char tmp[PROC_NUMBUF];
+        if (!tgid)
+                return -ENOENT;
+        sprintf(tmp, "%d", tgid);
+        return vfs_readlink(dentry,buffer,buflen,tmp);
+}
+
+static void *proc_self_follow_link(struct dentry *dentry, struct nameidata *nd)
+{
+        struct pid_namespace *ns = dentry->d_sb->s_fs_info;
+        pid_t tgid = task_tgid_nr_ns(current, ns);
+        char *name = ERR_PTR(-ENOENT);
+        if (tgid) {
+                /* 11 for max length of signed int in decimal + NULL term */
+                name = kmalloc(12, GFP_KERNEL);
+                if (!name)
+                        name = ERR_PTR(-ENOMEM);
+                else
+                        sprintf(name, "%d", tgid);
+        }
+        nd_set_link(nd, name);
+        return NULL;
+}
+
+static void proc_self_put_link(struct dentry *dentry, struct nameidata *nd,
+                                void *cookie)
+{
+        char *s = nd_get_link(nd);
+        if (!IS_ERR(s))
+                kfree(s);
+}
+
+static const struct inode_operations proc_self_inode_operations = {
+        .readlink       = proc_self_readlink,
+        .follow_link    = proc_self_follow_link,
+        .put_link       = proc_self_put_link,
+};
+
+void __init proc_self_init(void)
+{
+        struct proc_dir_entry *proc_self_symlink;
+        mode_t mode;
+
+        mode = S_IFLNK | S_IRWXUGO;
+        proc_self_symlink = proc_create("self", mode, NULL, NULL );
+        proc_self_symlink->proc_iops = &proc_self_inode_operations;
+}